SUSE Linux Enterprise Server 11 SP3

Virtualization with KVM

Publication Date 18 Nov 2013

Copyright © 2006–2013 SUSE LLC and contributors. All rights reserved.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or (at your option) version 1.3; with the Invariant Section being this copyright notice and license. A copy of the license version 1.2 is included in the section entitled GNU Free Documentation License.

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Contents

About This Manual
1. Available Documentation
2. Feedback
3. Documentation Conventions
I. Requirements, Limitations, and Support Status
1. KVM Installation and Requirements
1.1. Hardware Requirements
1.2. Supported Guest Operating Systems
1.3. The kvm package
1.4. Installing KVM
2. KVM Limitations
2.1. General Limitations
2.2. Hardware Limitations
2.3. Performance Limitations
3. KVM Support Status
3.1. Supported Features and Tools
3.2. Unsupported Features and Tools
II. Managing Virtual Machines with libvirt
4. Overview
5. Guest Installation
5.1. Guest Installation with Virtual Machine Manager
5.2. Installing from the Command Line with vm-install
5.3. Advanced Guest Installation Scenarios
6. Basic VM Guest Management
6.1. Listing VM Guests
6.2. Opening a Graphical Console
6.3. Changing a VM Guest's State: Start, Stop, Pause
6.4. Saving and Restoring VM Guests
6.5. Deleting a VM Guest
7. Connecting and Authorizing
7.1. Authentication
7.2. Configuring Remote Connections
7.3. Connecting to a VM Host Server
8. Managing Storage
8.1. Managing Storage with Virtual Machine Manager
8.2. Managing Storage with virsh
8.3. Locking Disk Files and Block Devices with virtlockd
9. Configuring Virtual Machines
9.1. Enabling Seamless and Synchronized Cursor Movement
9.2. Adding a CD/DVD-ROM Device with Virtual Machine Manager
9.3. Adding a Floppy Device with Virtual Machine Manager
9.4. Ejecting and Changing Floppy or CD/DVD-ROM Media with Virtual Machine Manager
9.5. Adding a PCI Device with Virtual Machine Manager
9.6. Adding a PCI Device with virsh
9.7. Clock Settings
10. Administrating VM Guests
10.1. Migrating VM Guests
10.2. Monitoring
III. Managing Virtual Machines with QEMU
11. QEMU Overview
12. Guest Installation
12.1. Basic Installation with qemu-kvm
12.2. Managing Disk Images with qemu-img
13. Running Virtual Machines with qemu-kvm
13.1. Basic qemu-kvm Invocation
13.2. General qemu-kvm Options
13.3. Using Devices in QEMU
13.4. Networking in QEMU
13.5. Viewing a VM Guest with VNC
13.6. VirtFS: Sharing Folders between Host and Guests
13.7. KSM: Sharing Memory Pages between Guests
14. KVM Disk Cache Modes
14.1. Disk Interface Cache Modes
14.2. Description of Cache Modes
14.3. Data Integrity Implications of Cache Modes
14.4. Performance Implications of Cache Modes
14.5. Effect of Cache Modes on Live Migration
15. Administrating Virtual Machines with QEMU Monitor
15.1. Accessing Monitor Console
15.2. Getting Information about the Guest System
15.3. Changing VNC Password
15.4. Managing Devices
15.5. Controlling Keyboard and Mouse
15.6. Changing Available Memory
15.7. Dumping Virtual Machine Memory
15.8. Managing Virtual Machine Snapshots
15.9. Suspending and Resuming Virtual Machine Execution
15.10. Live Migration
A. Appendix
A.1. Installing Paravirtualized Drivers
A.2. Generating x509 Client/Server Certificates
A.3. QEMU Command Line Options
B. GNU Licenses
B.1. GNU Free Documentation License

List of Figures

9.1. Details View of a VM Guest
12.1. New 2GB Partition in Guest YaST Partitioner
13.1. QEMU Window with SLES 11 SP1 as VM Guest
13.2. Configuring Network Bridge with YaST
13.3. QEMU VNC Session
13.4. Authentication Dialog in Vinagre

List of Tables

1.1. Supported Guest Operating Systems on KVM with SUSE Linux Enterprise Server

List of Examples

5.1. Interactive Setup on the Command Line Using vm-install
5.2. vm-install command line switches
10.1. Typical Output of kvm_stat
13.1. Restricted User-mode Networking
13.2. User-mode Networking with Custom IP Range
13.3. User-mode Networking with Network-boot and TFTP
13.4. User-mode Networking with Host Port Forwarding
13.5. Password Authentication
13.6. x509 Certificate Authentication
13.7. x509 Certificate and Password Authentication
13.8. SASL Authentication
13.9. Exporting Host's Filesystem with VirtFS

About This Manual

This manual offers an introduction to setting up and managing virtualization with KVM (Kernel-based Virtual Machine) on SUSE Linux Enterprise Server. The first part introduces KVM by describing it's requirements and SUSE's support status. The second part deals with managing KVM with libvirt, while the last part covers management with QEMU.

Many chapters in this manual contain links to additional documentation resources. This includes additional documentation that is available on the system as well as documentation available on the Internet.

For an overview of the documentation available for your product and the latest documentation updates, refer to http://www.suse.com/doc.

1. Available Documentation

We provide HTML and PDF versions of our books in different languages. The following manuals for users and administrators are available for this product:

Deployment Guide (↑Deployment Guide)

Shows how to install single or multiple systems and how to exploit the product inherent capabilities for a deployment infrastructure. Choose from various approaches, ranging from a local installation or a network installation server to a mass deployment using a remote-controlled, highly-customized, and automated installation technique.

Administration Guide (↑Administration Guide)

Covers system administration tasks like maintaining, monitoring, and customizing an initially installed system.

Security Guide (↑Security Guide)

Introduces basic concepts of system security, covering both local and network security aspects. Shows how to make use of the product inherent security software like AppArmor (which lets you specify per program which files the program may read, write, and execute), and the auditing system that reliably collects information about any security-relevant events.

Security and Hardening Guide (↑Security and Hardening Guide)

Deals with the particulars of installing and setting up a secure SUSE Linux Enterprise Server, and additional post-installation processes required to further secure and harden that installation. Supports the administrator with security-related choices and decisions.

System Analysis and Tuning Guide (↑System Analysis and Tuning Guide)

An administrator's guide for problem detection, resolution and optimization. Find how to inspect and optimize your system by means of monitoring tools and how to efficiently manage resources. Also contains an overview of common problems and solutions, and of additional help and documentation resources.

Virtualization with Xen (↑Virtualization with Xen)

Offers an introduction to virtualization technology of your product. It features an overview of the various fields of application and installation types of each of the platforms supported by SUSE Linux Enterprise Server as well as a short description of the installation procedure.

Virtualization with KVM

Offers an introduction to setting up and managing virtualization with KVM (Kernel-based Virtual Machine) on SUSE Linux Enterprise Server. Learn how to manage KVM with libvirt or QEMU. The guide also contains detailed information about requirements, limitations, and support status.

AutoYaST (↑AutoYaST)

AutoYaST is a system for installing one or more SUSE Linux Enterprise systems automatically and without user intervention, using an AutoYaST profile that contains installation and configuration data. The manual guides you through the basic steps of auto-installation: preparation, installation, and configuration.

Storage Administration Guide (↑Storage Administration Guide)

Provides information about how to manage storage devices on a SUSE Linux Enterprise Server.

In addition to the comprehensive manuals, several quick start guides are available:

Installation Quick Start (↑Installation Quick Start)

Lists the system requirements and guides you step-by-step through the installation of SUSE Linux Enterprise Server from DVD, or from an ISO image.

Linux Audit Quick Start

Gives a short overview how to enable and configure the auditing system and how to execute key tasks such as setting up audit rules, generating reports, and analyzing the log files.

AppArmor Quick Start

Helps you understand the main concepts behind AppArmor®.

Virtualization with Linux Containers (LXC) (↑Virtualization with Linux Containers (LXC))

Gives a short introduction to LXC (a lightweight virtualization method) and shows how to set up an LXC host and LXC containers.

Find HTML versions of most product manuals in your installed system under /usr/share/doc/manual or in the help centers of your desktop. Find the latest documentation updates at http://www.suse.com/doc where you can download PDF or HTML versions of the manuals for your product.

2. Feedback

Several feedback channels are available:

Bugs and Enhancement Requests

For services and support options available for your product, refer to http://www.suse.com/support/.

To report bugs for a product component, log in to the Novell Customer Center from http://www.suse.com/support/ and select My Support+Service Request.

User Comments

We want to hear your comments about and suggestions for this manual and the other documentation included with this product. Use the User Comments feature at the bottom of each page in the online documentation or go to http://www.suse.com/doc/feedback.html and enter your comments there.

Mail

For feedback on the documentation of this product, you can also send a mail to doc-team@suse.de. Make sure to include the document title, the product version, and the publication date of the documentation. To report errors or suggest enhancements, provide a concise description of the problem and refer to the respective section number and page (or URL).

3. Documentation Conventions

The following typographical conventions are used in this manual:

  • /etc/passwd: directory names and filenames

  • placeholder: replace placeholder with the actual value

  • PATH: the environment variable PATH

  • ls, --help: commands, options, and parameters

  • user: users or groups

  • Alt, Alt+F1: a key to press or a key combination; keys are shown in uppercase as on a keyboard

  • File, File+Save As: menu items, buttons

  • This paragraph is only relevant for the architectures amd64, em64t, and ipf. The arrows mark the beginning and the end of the text block.

  • Dancing Penguins (Chapter Penguins, ↑Another Manual): This is a reference to a chapter in another manual.

Part I.  Requirements, Limitations, and Support Status

Chapter 1. KVM Installation and Requirements

Abstract

KVM is a full virtualization solution for x86 processors supporting hardware virtualization (Intel VT or AMD-V). It consists of two main components: A set of Kernel modules (kvm.ko, kvm-intel.ko, and kvm-amd.ko) providing the core virtualization infrastructure and processor specific drivers and a userspace program (qemu-kvm) that provides emulation for virtual devices and control mechanisms to manage VM Guests (virtual machines). The term KVM more properly refers to the Kernel level virtualization functionality, but is in practice more commonly used to reference the userspace component.

VM Guests (virtual machines), virtual storage and networks can be managed with libvirt-based and QEMU tools. libvirt is a library that provides an API to manage VM Guests based on different virtualization solutions, among them KVM and Xen. It offers a graphical user interface as well as a command line program. The QEMU tools are KVM/QEMU specific and are only available for the command line.

1.1. Hardware Requirements

Currently, SUSE only supports KVM full virtualization on x86_64 hosts. KVM is designed around hardware virtualization features included in AMD (AMD-V) and Intel (VT-x) CPUs. It supports virtualization features of chipsets, and PCI devices, such as an I/O Memory Mapping Unit (IOMMU) and Single Root I/O Virtualization (SR-IOV)).

You can test whether your CPU supports hardware virtualization with the following command:

egrep '(vmx|svm)' /proc/cpuinfo

If this command returns no output, your processor either does not support hardware virtualization, or this feature has been disabled in the BIOS.

The following Web site identifies processors which support hardware virtualization: http://ark.intel.com/Products/VirtualizationTechnology (for Intel CPUs), and http://products.amd.com/ (for AMD CPUs).

[Note]

The KVM Kernel modules will not load if the CPU does not support hardware virtualization or if this feature is not enabled in the BIOS.

The general minimum hardware requirements for the VM Host Server are the same as outlined in Section “System Requirements for Operating Linux” (Chapter 2, Installation on x86, AMD64, Intel 64, and Itanium, ↑Deployment Guide). However, additional RAM for each virtualized guest is needed. It should at least be the same amount that is needed for a physical installation. It is also strongly recommended to have at least one processor core or hyper-thread for each running guest.

1.2. Supported Guest Operating Systems

The following table lists guest operating systems tested and their support status offered by SUSE. All guest operating systems are supported both fully virtualized and paravirtualized, with the exception of Windows guests, which are only supported fully virtualized and OES and Netware guests, which are supported only paravirtualized. All operating systems except Netware (32-bit only) are supported in both 32 and 64-bit x86 versions.

Para-virtualized drivers (PV drivers) are listed where available.

Para-virtualized drivers for KVM

  • virtio-net: Virtual network driver.

  • virtio-blk: Virtual block device driver for paravirtualized block devices.

  • virtio-balloon: Memory driver for dynamic memory allocation. Allows to dynamically change the amount of memory allocated to a guest.

  • virtio-scsi: Storage interface that supports advanced SCSI hardware.

  • kvm-clock: Clock synchronization driver.

Table 1.1. Supported Guest Operating Systems on KVM with SUSE Linux Enterprise Server

SLES 11 SP1/ SP2 / SP3

PV drivers:

kvm-clock, virtio-net, virtio-blk, virtio-balloon, virtio-console, virtio-rng

Support Status:

Fully supported (L3)

SLES 10 SP4

PV drivers:

kvm-clock, virtio-net, virtio-blk, virtio-balloon, virtio-console

Support Status:

Fully supported (L3)

SLES 9 SP4

PV drivers:

n/a

Support Status:

Fully supported (L3)

Mandatory boot parameters:

32 bit kernel: clock=pmtmr
64 bit kernel: ignore_lost_ticks

SLED 11 SP1 / SP2 / SP3

PV drivers:

kvm-clock, virtio-net, virtio-blk, virtio-balloon, virtio-console, virtio-rng

Support Status:

Technology Preview (L2)

RedHat Enterprise Linux 4.x / 5.x / 6.x

PV drivers:

See http://www.redhat.com/

Support Status:

Best Effort (L2)

Note:

Refer to the RHEL Virtualization guide for more information.

Windows 2003 SP2+ / 2008 SP2+ / 2008 R2+ / 2012

PV drivers:

virtio-net, virtio-blk, virtio-balloon; drivers from the Virtual Machine Driver Pack (http://www.suse.com/products/vmdriverpack/) are preferred

Support Status:

Fully supported with Server Virtualization Validation Program (SVVP) certification (fully virtualized)

Note:

Host processor must have constant_tsc CPU feature (check with the following command: grep "constant_tsc" /proc/cpuinfo).

Windows XP SP3+ / 2003 SP2+ / Vista SP2+ / 7 SP1+ / 8

PV drivers:

virtio-net, virtio-blk, virtio-balloon; drivers from the Virtual Machine Driver Pack (http://www.suse.com/products/vmdriverpack/) are preferred

Support Status:

Best effort (L2)


[Important]

Guest images created under SUSE Linux Enterprise Server 11 SP1 and newer are supported, but guest images created under a previous SUSE Linux Enterprise version are not supported.

1.2.1. Availability of Paravirtualized Drivers

To improve the performance of the guest operating system, paravirtualized drivers are provided when available. Although they are not required, it is strongly recommended to use them. The paravirtualized drivers are available as follows:

SUSE Linux Enterprise Server 11 SP1 / SP2 / SP3

included in Kernel

SUSE Linux Enterprise Server 10 SP4

included in Kernel

SUSE Linux Enterprise Server 9 SP4

not available

RedHat

available in RedHat Enterprise Linux 5.4 and newer

Windows

SUSE has developed virtio based drivers for Windows, which are available in the Virtual Machine Driver Pack (VMDP). See http://www.suse.com/products/vmdriverpack/ for more information.

1.3. The kvm package

The kvm package provides qemu-kvm, the program that performs the I/O emulation for the VM Guest. In addition to the qemu-kvm program, the kvm package also comes with a debug level monitoring utility (kvm_stat), firmware components, key-mapping files, and scripts. The deprecated Windows drivers (win-virtio-drivers.iso) are no longer provided. For more information, see Section A.3.1.1, “Deprecated features”.

Originally, the kvm package also provided the KVM Kernel modules. Now, these modules are included with the Kernel and only userspace components are included in the current kvm package.

Using the libvirt-based tools is the recommended way of managing VM Guests. Interoperability with other virtualization tools has been tested and is an essential part of SUSE's support stance. All tools are provided by packages carrying the tool's name.

  • libvirt: A toolkit that provides management of VM Guests, virtual networks, and storage. libvirt provides an API, a daemon, and a shell (virsh).

  • virt-manager (Virtual Machine Manager): A graphical management tool for VM Guests.

  • vm-install: Define a VM Guest and install its operating system.

  • virt-viewer: An X viewer client for VM Guests which supports TLS/SSL encryption of x509 certificate authentication and SASL authentication.

Support for creating and manipulating file-based virtual disk images is provided by qemu-img. qemu-img is provided by the package virt-utils.

1.4. Installing KVM

KVM is not installed by default. To install KVM and all virtualization tools, proceed as follows:

  1. Start YaST and choose Virtualization+Installing Hypervisor and Tools.

  2. Select KVM and confirm with Accept.

  3. Confirm the list of packages that is to be installed with Install.

  4. Agree to set up a network bridge by clicking Yes. It is recommended using a bridge on a VM Host Server (virtual machine host). If you prefer to manually configure a different network setup, you can safely skip this step by clicking No.

  5. After the setup has been finished, reboot the machine as YaST suggests. Alternatively load the required kernel modules manually and start libvirtd to avoid a reboot:

    modprobe kvm-intel # on Intel machines only
    modprobe kvm-amd   # on AMD machines only
    modprobe vhost-net
    rclibvirtd start
[Note]The vhost-net Kernel Module

The vhost-net kernel module allows for a more efficient network transport to the guest. It is automatically used by libvirt if loaded, or when using the qemu-kvm command line, by adding ,vhost=on to the networking option.

Chapter 2. KVM Limitations

Although virtualized machines behave almost like physical machines, some limitations apply. These affect both, the VM Guest as well as the VM Host Server system.

2.1. General Limitations

The following general restrictions apply when using KVM:

Overcommits

KVM allows for both memory and disk space overcommit. It is up to the user to understand the implications of doing so. However, hard errors resulting from exceeding available resources will result in guest failures. CPU overcommit is also supported but carries performance implications.

Time Synchronization

Most guests require some additional support for accurate time keeping. Where available, kvm-clock is to be used. NTP or similar network based time keeping protocols are also highly recommended (for VM Host Server and VM Guest) to help maintain a stable time. Running NTP inside the guest is not recommended when using the kvm-clock . Refer to Section 9.7, “Clock Settings” for details.

MAC addresses

If no MAC address is specified for a NIC, a default MAC address will be assigned. This may result in network problems when more than one NIC receives the same MAC address. It is recommended to always assure a unique MAC address has been assigned for each NIC.

Live Migration

Live Migration is only possible between VM Host Servers with the same CPU features. The only supported CPU model for migration is -cpu qemu64 (default) with no additional features specified. No physical devices can be passed from host to guest. Guest storage has to be accessible from both VM Host Servers and guest definitions need to be compatible. VM Host Server and VM Guests need to have proper timekeeping installed. The use of the AHCI interface, the virtfs feature, and the -mem-path command-line option are not compatible with migration. Migration from SP3 to SP2 or SP1 hosted guests is not supported.

User Permissions

The management tools (Virtual Machine Manager, virsh, vm-install) need to authenticate with libvirt—see Chapter 7, Connecting and Authorizing for details. In order to invoke qemu-kvm from the command line, a user has to be a member of the group kvm.

Suspending/Hibernating the VM Host Server

Suspending or hibernating the VM Host Server system while guests are running is not supported.

2.2. Hardware Limitations

The following virtual hardware limits for guests have been tested. We ensure host and VMs install and work successfully, even when reaching the limits and there are no major performance regressions (CPU, memory, disk, network) since the last release.

Max. Guest RAM Size

512 GB

Max. Virtual CPUs per Guest

64

Max. Virtual Network Devices per Guest

8

Max. Block Devices per Guest

4 emulated (IDE), 20 para-virtual (using virtio-blk), or 100 (virtio-scsi)

Max. Number of VM Guests per VM Host Server

Limit is defined as the total number of virtual CPUs in all guests being no greater than 8 times the number of CPU cores in the host.

2.3. Performance Limitations

Basically, workloads designed for physical installations can be virtualized and therefore inherit the benefits of modern virtualization techniques. However, virtualization comes at the cost of a slight to moderate performance impact. You should always test your workload with the maximum anticipated CPU and I/O load to verify if it is suited for being virtualized. Although every reasonable effort is made to provide a broad virtualization solution to meet disparate needs, there will be cases where the workload itself is unsuited for KVM virtualization.

We therefore propose the following performance expectations for guests performance to be used as a guideline. The given percentage values are a comparison of performance achieved with the same workload under non-virtualized conditions. The values are rough approximations and cannot be guaranteed.

Category

Fully Virtualized

Paravirtualized

Host Pass-through

CPU, MMU

7%

not applicable

97% (Hardware Virtualization with Extended Page Tables (Intel) or Nested Page Tables (AMD)
85% (Hardware Virtualization with shadow page tables)

Network I/O (1GB LAN)

60% (e1000 emulated NIC)

75% (virtio-net)

95%

Disk I/O

40% (IDE emulation)

85% (virtio-blk)

95%

Graphics (non-accelerated)

50% (VGA or Cirrus)

not applicable

not applicable

Time accuracy (worst case, using recommended settings without NTP)

95% - 105% (where 100% = accurate)

100% (kvm-clock)

not applicable

Chapter 3. KVM Support Status

The following list contains features and tools as supported by SUSE—this does not necessarily reflect the support status of the software itself. For a list of qemu-kvm command switches supported by SUSE, refer to Section A.3, “QEMU Command Line Options”.

3.1. Supported Features and Tools

vm-install

Define and install VM Guests via vm-install including specifying the number of virtual processors, RAM, disk type and location, video type, keyboard mapping, NIC type, binding, MAC address, and boot method.

Restrictions: Currently only the raw, qcow2 and qed disk formats are supported. NIC creation is restricted to using Realtek, e1000 or virtio NICs. Sound cards are not supported.

Virtual Machine Manager

Manage guests via Virtual Machine Manager using the following functions: autostart, start, stop, restart, pause, unpause, save, restore, clone, migrate, special key sequence insertion, guest console viewers, performance monitoring, and CPU pinning. Furthermore, static modifications of CPU, RAM, boot method, disk, NIC, mouse, display, video and host PCI and USB assignments are supported.

Restrictions: The following features are currently not supported: sound devices, qxl, vmvga (vmware), Xen video, pcnet, ne2k_pci, eepro100, emulated SCSI disks, Spice graphics. Raw, qed, and qcow2 are the only supported storage formats.

virsh

Manage guests via the command line.

Most virsh subcommands are supported, including creation, modification, and destruction of guests and all life cycle operations. Any virsh subcommands which translate to unsupported qemu-kvm command-line or monitor syntax are also unsupported. Guest XML descriptions used by virsh can be created manually, using vm-install, the Virtual Machine Manager, or external tools and scripts.

qemu-kvm

Manage guests via the command line. Although managing via Virtual Machine Manager should be the preferred option, qemu-kvm may be used for greater flexibility. See Section A.3.1, “Supported qemu-kvm Command Line Options” for a list of supported options.

Restrictions: See Section A.3.2, “Unsupported qemu-kvm Command Line Options” for a list of not supported options.

kvm_stat

Debugging and monitoring tool.

USB Host Device Pass-through

A physical USB device may be passed from the VM Host Server to the VM Guest. Given the very wide variety of USB devices available, it is anticipated that some devices may not work properly.

PCI Pass-through

PCI Pass-through improves performance of PCI devices. It requires underlying support from the hardware (e.g. Intel VT-d extensions, or AMD IOMMU extensions). VT-d requires the Kernel parameter "intel_iommu=on". Additionally, some host hardware will require the use of the KVM Kernel module parameter: allow_unsafe_assigned_interrupts=1 (enabling this parameter has security implications).

Many PCIe cards from major vendors should be supportable. Refer to system level certifications for specific details, or contact the vendor for support statements.

Device hotplugging

Dynamically adding or removing emulated or pass-through physical devices in the VM Guest is supported.

Memory ballooning

Dynamically changing the amount of memory allocated to a guest is supported.

Sharing Folders between VM Host Server and VM Guest

Sharing folders between host and VM Guest is supported via VirtFs.

Kernel Samepage Merging (KSM)

KSM allows for automatic sharing of identical memory pages between guests to save host memory. KVM is optimized to use KSM if enabled on the VM Host Server.

Transparent Huge Pages (THP)

THP allows CPUs to address memory using pages larger than the default 4 KB. This helps reducing memory consumption and CPU cache usage. KVM is optimized to use THP (via madvise and opportunistic methods) if enabled on the VM Host Server.

KVM Security

A kvm group is created by the KVM package, which permits a non-root user to access the KVM control device file (/dev/kvm). Where possible, guests should not be run as root. Steps have been taken to enable this for libvirt as well. A setuid bridge helper has been added so that a bridged network interface can be set up without needing root privileges.

Seccomp2 based sandboxing

The VM Guest can be run in a sandboxed environment where only predetermined system calls are permitted for added protection against malicious behavior.

APIC Virtualization

Hardware APIC Virtualization, allowing the processor to directly inject interrupts into the VM Guest to achieve better performance, is supported.

VirtFS (file system pass-through)

Directories in the host file system can be shared between the host and VM Guest or guests using virtfs. A virtfs proxy helper is provided to enable virtfs usage when KVM is used as non-root user.

Vhost-net kernel module support

The vhost-net kernel module allows for a more efficient network transport to the VM Guest. It is automatically used by libvirt if loaded, or when using the qemu-kvm command line, by adding vhost=on to the networking option.

AHCI guest storage interface

The AHCI interface for SATA storage has been recently added. It permits much higher block I/O performance than the IDE interface, and is particularly useful for use in recent Windows OS versions.

qcow2 and qed storage formats

qcow2 and qed storage formats can now be used with live migration.

Trim and Online Disk Resizing

Trim and online disk resizing support depends on the storage format used.

Virtio SCSI

Virtio SCSI allows for passing through host SCSI block or generic SCSI devices to the VM Guest, and provides additional storage options in a virtio SCSI interface within the guest.

Macvtap / vhost-net zero-copy transmits

Zero-copy packet transmits from the VM Guest are now possible using vhost-net and macvtap changes that have been added to the latest kernels.

Disk caching modes

The default caching mode for disk images is now writeback due to improvements in the handling of the image format. The virtio-blk back-end now automatically switches from 'writeback' to 'writethrough' if the VM Guest virtio driver does not support flushes.

Non-Uniform Memory Access (NUMA)

NUMA machines are supported. Using numactl to pin qemu-kvm processes to specific nodes is recommended.

3.2. Unsupported Features and Tools

Power Management

Changing power states in the host while guests are running is not supported.

Virtio-data-block - data-plane

An experimental block I/O back-end is available using the, x-data-plane=on parameter to -device virtio-blk-pci. This interface allows higher I/O rates. This is not yet supported.

Q35 Machine

A more modern machine type based on the Intel q35 chipset is available. This is not yet supported.

Nested Virtualization

When the svm or vmx CPU feature is passed through to the VM Guest, nested virtualization is possible. This is not yet supported.

Spice

Spice interoperability is not supported.

Glusterfs

Glusterfs interoperability is not supported.

ISCSI

ISCSI integration is not supported. It is however possible for guests to access ISCSI targets available to the host via the blockio interfaces.

RBD (Rados Block Devices)

RBD integration is not supported.

CPU hotplugging

Dynamically changing the number of virtual CPUs assigned to the VM Guest is currently not supported.

KVM Kernel Module Parameters

Specifying parameters for the KVM Kernel modules is currently not supported unless done under the direction of SUSE support personnel.

Guest Agent

The guest agent (qemu-ga) allows programs on the VM Host Server to directly communicate with a VM Guest via an emulated or paravirtualized serial console. This feature is currently not supported.

Using QEMU without KVM (TCG (Tiny Code Generator) mode)

qemu-kvm can be invoked with the -no-kvm parameter. In this case VM Guest CPU instructions are emulated instead of being executed directly by the processor. This mode is not supported, but may be useful for problem resolution.

Part II. Managing Virtual Machines with libvirt

Chapter 4. Overview

libvirt is a library that provides a common API for managing popular virtualization solutions, among them KVM and Xen. The library provides a normalized management API for these virtualization solutions, allowing a stable, cross-hypervisor interface for higher-level management tools. The library also provides APIs for management of virtual networks and storage on the VM Host Server. The configuration of each VM Guest is stored in an XML file.

With libvirt you can also manage your VM Guests remotely. It supports TLS encryption and x509 certificates as well as authentication with SASL.

The communication between the virtualization solutions and libvirt is managed by the daemon libvirtd. It is also used by the management tools. libvirtd needs to run on the VM Host Server and on any remote machine on which the libvirt-based tools are started. Use the following commands to start, stop it or check its status:

~ # rclibvirtd start
Starting libvirtd                              done
~ # rclibvirtd status
Checking status of libvirtd                 running
~ # rclibvirtd stop
Shutting down libvirtd                         done
~ # rclibvirtd status
Checking status of libvirtd                  unused

To automatically start libvirtd at boot time, either activate it using the YaST System Services (Runlevel) module or by entering the following command:

insserv libvirtd

The following libvirt-based tools are available on SUSE Linux Enterprise Server:

Virtual Machine Manager (virt-manager)

The Virtual Machine Manager is a desktop tool for managing VM Guests. It provides the ability to control the life cycle of existing machines (bootup/shutdown, pause/resume, suspend/restore). It lets you create new VM Guests and various types of storage, and manage virtual networks. Access the graphical console of VM Guests with the built-in VNC viewer, and view performance statistics, all done locally or remotely.

The Virtual Machine Manager does not need to run on the VM Host Server, it also lets you control VM Guests via remote connections. This enables you to manage VM Guests centrally from a single workstation without having to log in on the VM Host Server.

To start the Virtual Machine Manager, enter virt-manager at the command prompt.

virt-viewer

A viewer for the graphical console of a VM Guest. It uses the VNC protocol and supports TLS and x509 certificates. VM Guests can be accessed by name, ID, or UUID. If the guest is not already running, the viewer can be told to wait until the guest starts, before attempting to connect to the console.

vm-install

A tool to set up a VM Guest, configure its devices and start the operating system installation. Starts a GUI wizard when called from a graphical user interface. When invoked on a terminal, starts the wizard in command-line mode. vm-install is also started when creating a new virtual machine in the Virtual Machine Manager.

virsh

A command line tool to manage VM Guests with similar functionality as the Virtual Machine Manager. Allows you to change a VM Guest's status (start, stop, pause, etc.) to set up new guests and devices and to edit existing configurations. virsh is also useful to script VM Guest management operations.

virsh basically works like Subversion's svn command or zypper: it takes the first arguments as a command and further arguments as options to this command:

virsh [-c URI] commanddomain-id [OPTIONS]

Just like zypper, virsh can also be called without a command. In this case it starts a shell waiting for your commands. This mode is useful when having to run subsequent commands:

~> virsh -c qemu+ssh://wilber@mercury.example.com/system
Enter passphrase for key '/home/wilber/.ssh/id_rsa': 
Welcome to virsh, the virtualization interactive terminal.

Type:  'help' for help with commands
       'quit' to quit

virsh # hostname
mercury.example.com

Chapter 5. Guest Installation

A VM Guest is comprised of an image containing an operating system and data files and a configuration file describing the VM Guest's virtual hardware resources. VM Guests are hosted on and controlled by the VM Host Server.

5.1. Guest Installation with Virtual Machine Manager

Clicking New in the Virtual Machine Manager launches vm-install. It provides the graphical Create Virtual Machine Wizard that guides you through the guest installation. vm-install can also be run directly from the command-line or from YaST by choosing Virtualization+Create Virtual Machine.

  1. Start the Create Virtual Machine Wizard as described above and click Forward.

  2. Choose whether to install an operation system or an already existing image or disk.

  3. Select the operating system you want to install from the list. Each entry provides reasonable defaults for the chosen operating system.

  4. The Summary page shows the default configuration for the chosen operating system. Edit the configuration by clicking on a headline. When having chosen to install a system, you at least have to specify either an image or a CD/DVD device from which to boot or choose PXE boot. When accepting the configuration with OK, the guest system boots to start the installation.

5.1.1. Customizing the Default Settings

Change the proposed configuration by clicking on a headline in the Summary page of the Create Virtual Machine Wizard:

5.1.1.1. Name of Virtual Machine

Specify a Name and an optional Description for the guest. The Name must contain only alphanumeric and _-.:+ characters. It must be unique among all VM Guests on the VM Host Server. It is used to create and name the guest’s configuration file and you will be able to access the guest with this name from virsh.

5.1.1.2. Hardware

Change memory and CPU assignments in this screen. It is recommended not to specify values larger than the resources the VM Host Server can provide (overcommit), since it may result in errors or performance penalties.

This dialog also allows you to assign PCI devices (for example a network card) that can be directly used by the VM Guest (PCI passthrough). Click Host Devices+Manage VM Devices to get a list of available devices. Choose a device from the list and click Add to add it to the devices list for the VM Guest. It is recommended to activate the Managed option for each device—it assures that libvirt automatically takes care of binding and unbinding drivers—see 'managed' vs. 'unmanaged' for more information.

[Important]PCI devices cannot be shared

PCI devices cannot be shared between host and VM Guest or between VM Guests—each device can only be used by a single instance. Make sure to only add PCI devices not used elsewhere.

The Advanced Settings lets you activate or deactivate ACPI, APIC, and PAE. It is recommended not to change the default settings. You can also enable or disable paravirtualized I/O with virtio or choose to execute the kernel on boot (linux only) here.

[Important]Para-Virtualized I/O

If you enable paravirtualized I/O by activating virtio, all hard disks you create will be configured as virtio disks. If your operating system does not have appropriate drivers, the installation will fail. A Windows operating system installation even fails if providing a driver. By default, this feature is only activated for operating systems known to ship with virtio drivers.

5.1.1.3. Peripheral Devices

Configure the type of virtualized graphics hardware, the keymap and sound device in this dialog. If you disable the graphics card support, the machine is only accessible via network services (ssh) or serial port. Sound in VM Guests is currently not supported by SUSE, therefore Sound should be set to None.

5.1.1.4. Disks

Disks: Manage virtual hard disks and CD/DVD drives in this dialog. A VM Guest must have at least one virtual disk—either an existing one or a newly created disk. Virtual disks can be:

  • a single file with a fixed size

  • a single file that grows on demand (Sparse Image File)

    [Important]Sufficient Space for Sparse Image Files

    When creating sparse image files, the partition on which you create them always needs sufficient free space. The VM Guest has no means to check the VM Host Server disk space. Having no space left on the host partition causes write errors and loss of data on the guest system.

  • a block device, such as an entire disk, partition, or a network volume.

For best performance, create each virtual disk from an entire disk or a partition. For the next best performance, create an image file but do not create it as a sparse image file. A virtual disk based on a sparse image file delivers the most disk space flexibility but slows installation and disk access speeds.

[Tip]Live Migration

If you need to be able to migrate your VM Guest to another host without shutting it down (live migration), all disks must reside on a network resource (network file system or iSCSI volume) that is accessible from both hosts.

By default, a single sparse raw disk image file is created in /var/lib/kvm/images/VM_NAME/ where VM_NAME is the name of the virtual machine.

[Note]Supported Disk format

Currently, only the disk formats raw, qed and qcow2 are supported by SUSE.

Procedure 5.1. Creating a Virtual Disk

  1. Click Harddisk.

  2. Enter a Source. If creating a file-backed disk, either enter the path directly or click New. When creating a disk from a device, enter the device node, for example /dev/disk/by-path/path. It is strongly recommended not to use the simple device paths such as /dev/sdb or /dev/sda5, since they may change (by adding a disk or by changing the disk order in the BIOS).

  3. Specify the Protocol. For creating raw disks, choose either file for file-backed virtual disks or phy for device-backed disks. qcow2 or qed disks can be created by choosing the corresponding value.

  4. Enter a Size in GB. This option is only available for file-backed disks.

  5. Choose whether to create a Sparse Image File. This option is only available for file-backed disks. If you want to disable write-access to the disk, choose Read-Only Access.

If you want to install from DVD or CD-ROM, add the drive to the list of available hard disks. To learn about device nodes of the available optical drives, run:

hwinfo --cdrom | egrep "(Device File:|Model:)"

Instead of the real DVD or CD-ROM drive, you can also add the ISO image of an installation medium. Note that each CD-Rom drive or ISO image can only be used by one guest at the same time.

To add a CD/DVD-ROM device or an ISO image, proceed as follows:

  1. Click CD-ROM.

  2. Enter a Source. If adding a device, enter its node. If adding an ISO image, either enter the path directly or click Browse to open a file browser.

  3. Specify the Protocol. Choose file for an ISO image and phy for a device.

The disks are listed in the order in which they have been created. This order also represents the boot order. Use the Up and Down arrows to change the disk order.

5.1.1.5. Network Adapters

By default, a single virtual network card is created for the virtual machine. It has a randomly generated MAC address that you can change to fit your desired configuration. If a bridge exists on the VM Host Server, the virtual network card will be attached to it, otherwise it will be attached to the libvirt's default virtual bridge (virbr1).

To add a new network adapter or edit an existing one, proceed as follows:

  1. Click New to add a card or Edit to change the configuration of the selected card.

  2. Choose a Type from the drop-down list.

    [Note]Supported Virtual Network Adapter Types

    Currently, only Fully Virtualized Realtek 8139, Fully Virtualized Intel e1000 or the paravirtualized QEMU Virtualized NIC Card (virtio) are supported by SUSE.

  3. Choose a Source from the drop-down list.

  4. Choose whether to assign a randomly generated MAC address or manually specify an address.

    [Note]MAC addresses need to be unique

    When choosing to manually specify a MAC address, make sure it is not already used in your network. If so, it may result in network problems, especially when using DHCP. Therefore avoid specifying obvious MAC addresses such as 52:54:00:12:34:56 or 52:54:00:11:22:33, because they may already be in use. It is strongly recommended to always use a randomly generated MAC address for each adapter.

5.1.1.6. Operating System Installation

This dialog is only available when having chosen to install an operating system. The installation can be booted from a virtual disk, from a CD/DVD device, from an ISO image, a network resource or via PXE boot—use this dialog to configure the boot device.

Also use this dialog to configure the behavior of the VM Guest when the operating system is powered off, rebooted or if it crashes. The following options are available

destroy

normal cleanup

restart

a new VM Guest is started in place of the old one

preserve

no cleanup, do not delete temporary, configuration and image files

rename-restart

the VM Guest is not cleaned up but is renamed and a new domain started in its place

coredump-destroy

a crashed machine's core is dumped before a normal cleanup is performed

coredump-restart

a crashed machine's core is dumped before a normal restart is performed

5.2. Installing from the Command Line with vm-install

If $DISPLAY is not set (for example, when operating on a console or on an ssh shell with no X-forwarding), vm-install offers a command-line wizard to interactively set up a VM Guest for installation. Once the setup is completed, the newly created guest boots into the installation system which can be connected via VNC.

[Important]Graphical User Interface needed for Installation

Once the VM Guest boots into the installation, you need to connect to the graphical console via VNC to attend the installation. Therefore, you need to start the viewer from a graphical user interface.

If you are working from a console with no access to a graphical user interface, you can set up the VM Guest configuration and start the installation at a later time. Refer to Section 5.2.1, “Defining a VM Guest without Starting the Installation” for instructions.

To start the wizard, just type vm-install to start. For a lot of parameters, the installation wizard already provides reasonable defaults which you can confirm by just pressing Enter. Here is a log of an interactive setup for a SUSE Linux Enterprise Server 11 installation:

Example 5.1. Interactive Setup on the Command Line Using vm-install

~ # vm-install 
Gathering settings...

Please specify the type of operating system that will run within the virtual
machine.  This defines many defaults, and helps decide how to start
paravirtualized operating systems.
Press 'q' or the Escape key to exit.
  1: Novell Open Enterprise Server 2 (Linux)
  2: Novell Open Enterprise Server 2 (NetWare)
  3: Other operating system
  4: PXE
  5: RedHat (other)
  6: RedHat Enterprise Linux 3
  7: RedHat Enterprise Linux 4
  8: RedHat Enterprise Linux 5
  9: SUSE (other)
 10: SUSE Linux Enterprise Desktop 10
 11: SUSE Linux Enterprise Desktop 11
 12: SUSE Linux Enterprise Server 8
 13: SUSE Linux Enterprise Server 9
 14: SUSE Linux Enterprise Server 10
 15: SUSE Linux Enterprise Server 11
 16: Solaris 9 and older
 17: Solaris 10
 18: Windows (other)
 19: Windows (other, x64)
 20: Windows NT
 21: Windows Server 2008
 22: Windows Server 2008 (x64)
 23: Windows Vista, Windows 7
 24: Windows Vista, Windows 7 (x64)
 25: Windows XP, 2000, 2003
 26: Windows XP, 2003 (x64)
 27: openSUSE
 28: openSUSE 11
[15] >

PXE Boot
(Y / N) [N] >  
Please choose a name for the virtual machine.
[sles11] > 

Description > SLES 11 SP1

Specify the amount of memory and number of processors to allocate for the VM.
Initial Memory [512] > 
Maximum Memory [512] > 768
Warning: Setting the maximum memory greater than the initial memory requires
the VM operating system to have a memory balloon driver.
Virtual Processors [2] >

Please specify the type of virtualized graphics hardware.
  1: Cirrus Logic GD5446 VGA
  2: No Graphics Support
  3: VESA VGA
[1] > 

Virtual Disks:
  (None)
Do you want to add another virtual disk?
(Y / N) [Y] > 

Create a virtual disk based on a device (CD or other block device), an existing
image file (ISO), or a new file.  Specify a device by its device node, such as
/dev/cdrom, not its mount point.
What type of virtual disk do you want to add?
  1: CD-ROM or DVD
  2: Floppy
  3: Hard Disk
[3] > 3
Where will the virtual disk physically reside?
[/var/lib/kvm/images/sles11/hda] > 
Size (GB) [4.0] > 8.0
Create a sparse image file for the virtual disk?
(Y / N) [Y] > 

Virtual Disks:
  8.0 GB Hard Disk (file:/var/lib/kvm/images/sles11/hda)
Do you want to add another virtual disk?
(Y / N) [N] > y

Create a virtual disk based on a device (CD or other block device), an existing
image file (ISO), or a new file.  Specify a device by its device node, such as
/dev/cdrom, not its mount point.
What type of virtual disk do you want to add?
  1: CD-ROM or DVD
  2: Floppy
  3: Hard Disk
[3] > 1
Where will the virtual disk physically reside?
[/var/lib/kvm/images/sles11/hdb] > /isos/SLES-11-SP1-CD-i386-GM-CD1.iso

Virtual Disks:
  8.0 GB Hard Disk (file:/var/lib/kvm/images/sles11/hda)
  2.9 GB CD-ROM or DVD (file:/isos/SLES-11-SP1-DVD-x86_64-GM-DVD1.iso)
Do you want to add another virtual disk?
(Y / N) [N] > 

Network Adapters
  (None)
Do you want to add another virtual network adapter?
(Y / N) [Y] > 
What type of virtual network adapter do you want to add?
  1: Fully Virtualized AMD PCnet 32
  2: Fully Virtualized Intel e100
  3: Fully Virtualized Intel e1000
  4: Fully Virtualized NE2000 (ISA Bus)
  5: Fully Virtualized NE2000 (PCI Bus)
  6: Fully Virtualized Realtek 8139
  7: Paravirtualized
[6] > 7

Network Adapters
  Paravirtualized; Randomly generated MAC address
Do you want to add another virtual network adapter?
(Y / N) [N] > 

Preparing to start the installation...

Installing...

You may also provide parameters on the command line. The wizard will then prompt you for any missing parameters. In the following all parameters from Example 5.1, “Interactive Setup on the Command Line Using vm-install for which a command line switch exists, are specified. See man 8 vm-install for a full list of parameters.

Example 5.2. vm-install command line switches

vm-install --os-type sles111 --name "sles11_test"2 \
--vcpus 23 --memory 5124 --max-memory 7685 \
--disk /var/lib/kvm/images/sles11/hda,0,disk,w,8000,sparse=1 6 \
--disk /iso/SLES-11-SP1-DVD-x86_64-GM-DVD1.iso,1,cdrom7 \
--nic mac=52:54:00:05:11:11,model=virtio8 \
--graphics cirrus9 --config-dir "/etc/libvirt/qemu"10

1

Specifies the guest operating system to define suitable defaults. A list of valid values can be obtained with vm-install -O.

2

Name of the VM Guest. This name must be unique.

3

Number of virtual processors.

4

Initial amount of memory.

5

Maximum amount of memory. Requires an operating system with a paravirtualized virtio-balloon driver.

6

Defines a virtual hard disk. The file is located at /var/lib/kvm/images/sles11/hda. It is configured as the first (0) hard disk (disk). It is writable (w) with a size of 8 GB (8000). The file on the VM Host Server is a sparse file (sparse=1).

7

Defines an ISO image for a CD-ROM as the second (1) block device.

8

Configures a paravirtualized network device with the MAC address 52:54:00:05:11:11.

9

Specifies the graphics card.

10

The directory in which the XML configuration file for the virtual machine will be stored. It is strongly recommended to use the default directory /etc/libvirt/qemu.

5.2.1. Defining a VM Guest without Starting the Installation

vm-install provides the --no-install parameter. With this parameter the XML configuration file defining the VM Guest is created, but the guest is not booted automatically. You may use it regardless whether you start vm-install in wizard mode or whether you specify all other options in the command line. You can start the installation.

[Warning]No Virtual Disk Creation

When using the --no-install parameter with vm-install, no virtual disks will be created. Therefore, you have to create the disks in advance using either qemu-img or virsh.

Once the VM Guest XML configuration file is successfully created, you need to register it so it is recognized by Virtual Machine Manager or virsh. Do so by running:

virsh -c qemu:///system define PATH_TO_XMLFILE

5.3. Advanced Guest Installation Scenarios

This section provides instructions for operations exceeding the scope of a normal installation, such as including add-on packages.

5.3.1. Including Add-On Products in the Installation

Some operating systems such as SUSE Linux Enterprise Server offer to include add-on products in the installation process. In case the add-on product installation source is provided via network, no special VM Guest configuration is needed. If it is provided via CD/DVD or ISO image, it is necessary to provide the VM Guest installation system with both, the standard installation images and the image for the add-on product.

First add the standard installation image, and second the physical CD/DVD-ROM or add-on image. The image or device added first is automatically chosen as the boot image. In case you install SUSE Linux Enterprise Server, it will be configured as /dev/sr0, while the add-on product source will be configured as /dev/sr1.

Chapter 6. Basic VM Guest Management

Basic management tasks such as starting or stopping a VM Guest, can either be done using the graphical application Virtual Machine Manager or on the command line using virsh. Connecting to the graphical console via VNC is only possible from a graphical user interface.

6.1. Listing VM Guests

In order to be able to list VM Guests, you need to connect to a VM Host Server first. If you start the management tool on the VM Host Server itself, you are automatically connected. When operating from remote, refer to Section 7.3, “Connecting to a VM Host Server” for instructions.

6.1.1. Listing VM Guests with Virtual Machine Manager

The main Window of the Virtual Machine Manager shows a list of all VM Guests for each VM Host Server it is connected to. Each VM Guest entry contains the machine's name, its status (Running, Paused, or Shutoff) displayed as icon and literal, and a CPU usage bar.

6.1.2. Listing VM Guests with virsh

Use the command virsh list to get a list of VM Guests:

List running guests on localhost
virsh -c qemu:///system list
List running and inactive guests as user wilber on a remote host over a TLS connection
virsh -c qemu+tls://wilber@mercury.example.com/system list --all
List running and inactive guests as user tux on a remote host over an SSH tunnel
virsh -c qemu+ssh://tux@mercury.example.com/system list --inactive

6.2. Opening a Graphical Console

Opening a Graphical Console to a VM Guest lets you interact with the machine like a physical host via a VNC connection. If accessing the VNC server requires authentication, you are prompted to enter a username (if applicable) and a password.

Once you click into the VNC console, the cursor is grabbed and cannot be used outside the console anymore. To release it, press Alt+Ctrl.

[Tip]Seamless (Absolute) Cursor Movement

In order to prevent the console from grabbing the cursor and to enable seamless cursor movement, add a tablet input device to the VM Guest. See Section 9.1, “Enabling Seamless and Synchronized Cursor Movement” for more information.

Certain key combinations such as Ctrl+Alt+Del are interpreted by the host system and are not passed to the VM Guest.

To pass such key combinations to a VM Guest, open the Send Key menu from the VNC window and choose the desired key combination entry. The Send Key menu is only available when using Virtual Machine Manager and virt-viewer

[Note]Supported VNC Viewer

Principally all VNC viewers are able to connect to the console of a VM Guest. However, if you are using SASL authentication and/or TLS/SSL connection to access the guest, the options become limited. Common VNC viewers such as tightvnc or tigervnc support neither SASL authentication or TSL/SSL. The only supported alternative to Virtual Machine Manager and virt-viewer is vinagre.

6.2.1. Opening a Graphical Console with Virtual Machine Manager

  1. In the Virtual Machine Manager, right-click a VM Guest entry.

  2. Choose Open from the pop-up menu.

6.2.2. Opening a Graphical Console with virt-viewer

virt-viewer is a simple VNC viewer with added functionality for displaying VM Guest consoles. It can, for example, be started in wait mode, where it waits for a VM Guest to start before it connects. It also supports automatically reconnecting to a VM Guest that is rebooted.

virt-viewer addresses VM Guests by name, by ID or by UUID. Use virsh list --all to get this data.

To connect to a guest that is running or paused, either use the ID, UUID, or name. VM Guests that are shut off do not have an ID—you can only connect by UUID or name.

Local connect to guest with ID 8
virt-viewer -c qemu:///system 8
Local connect to the inactive guest sles11; will connect once the guest starts
virt-viewer -c qemu:///system --wait sles11

With the --wait option, the connection will be upheld even if the VM Guest is not running at the moment. Once the guest starts, the viewer will be launched.

Remote connect via ssh:
virt-viewer -c qemu+ssh://tux@mercury.example.com/system -w sles11

For more information, see virt-viewer --help or man 1 virt-viewer.

6.3. Changing a VM Guest's State: Start, Stop, Pause

Starting, stopping or pausing a VM Guest can either be done with Virtual Machine Manager or virsh. You can also configure a VM Guest to be automatically started when booting the VM Host Server.

When shutting down a VM Guest, you may either shut it down gracefully, or force the shutdown. The latter is equivalent to pulling the power plug on a physical host and is only recommended if there are no alternatives. Forcing a shutdown may cause file system corruption and loss of data on the VM Guest.

[Tip]Graceful Shutdown

In order to be able to perform a graceful shutdown, the VM Guest must be configured to support ACPI. If you have created the guest with vm-install or with Virtual Machine Manager, ACPI should be available. Use the following procedure in Virtual Machine Manager to check:

Double-click the VM Guest entry in Virtual Machine Manager. Choose View+Details and then Overview+Machine Settings. ACPI should be checked.

Depending on the guest operating system, enabling ACPI may not be sufficient. It is strongly recommended to test shutting down and rebooting a guest before releasing it to production. openSUSE or SUSE Linux Enterprise Desktop, for example, may require PolicyKit authorization for shutdown and reboot. Make sure this policy is turned off on all VM Guests.

If ACPI was enabled during a Windows XP/Server 2003 guest installation, turning it on in the VM Guest configuration alone is not sufficient. See the following articles for more information:

http://support.microsoft.com/kb/314088/EN-US/
http://support.microsoft.com/?kbid=309283

A graceful shutdown is of course always possible from within the guest operating system, regardless of the VM Guest's configuration.

6.3.1. Changing a VM Guest's State with Virtual Machine Manager

Changing a VM Guest's state can either be done from Virtual Machine Manager's main window, or from a VNC window.

Procedure 6.1. State Change from the Virtual Machine Manager Window

  1. Right-click on a VM Guest entry.

  2. Choose Run, Pause, or one of the Shutdown options from the pop-up menu.

Procedure 6.2. State change from the VNC Window

  1. Open a VNC Window as described in Section 6.2.1, “Opening a Graphical Console with Virtual Machine Manager”.

  2. Choose Run, Pause, or one of the Shut Down options either from the toolbar or from the Virtual Machine menu.

6.3.1.1. Autostarting a VM Guest

Automatically starting a guest when the VM Host Server boots is not enabled by default. This feature needs to be turned on for each VM Guest individually. There is no way to activate it globally.

  1. Double-click the VM Guest entry in Virtual Machine Manager to open its console.

  2. Choose View+Details to open the VM Guest configuration window.

  3. Choose Boot Options and check Start virtual machine on host boot up.

  4. Save the new configuration with Apply.

6.3.2. Changing a VM Guest's State with virsh

In the following examples the state of a VM Guest named sles11 is changed.

Start
virsh -c qemu:///system start sles11
Pause
virsh -c qemu:///system suspend sles11
Reboot
virsh -c qemu:///system reboot sles11
Graceful shutdown
virsh -c qemu:///system shutdown sles11
Force shutdown
virsh -c qemu:///system destroy sles11
Turn on autostart
virsh -c qemu:///system autostart sles11
Turn off autostart
virsh -c qemu:///system autostart --disable sles11

6.4. Saving and Restoring VM Guests

Saving a VM Guest preserves the exact state of the guest’s memory. The operation is slightly similar to hibernating a computer. A saved VM Guest can be quickly restored to its previously saved running condition.

When saved, the VM Guest is paused, its current memory state is saved to disk, and then the guest is stopped. The operation does not make a copy of any portion of the VM Guest’s virtual disk. The amount of time to save the virtual machine depends on the amount of memory allocated. When saved, a VM Guest’s memory is returned to the pool of memory available on the VM Host Server.

The restore operation loads a VM Guest’s previously saved memory state file and starts it. The guest is not booted but rather resumes at the point where it was previously saved. The operation is slightly similar to coming out of hibernation.

The VM Guest is saved to a state file. Make sure there is enough space on the partition you are going to save to. Issue the following command on the guest to get a rough estimation of the file size in megabytes to be expected:

free -m | awk '/^Mem:/ {print $3}'
[Warning]

After using the save operation, do not boot, start, or run the saved VM Guest. Doing so would cause the machine's virtual disk and the saved memory state getting out of sync and can result in critical errors when restoring the guest.

6.4.1. Saving / Restoring with Virtual Machine Manager

Procedure 6.3. Saving a VM Guest

  1. Open a VNC connection window to a VM Guest. Make sure the guest is running.

  2. Choose Virtual Machine+Save

  3. Choose a location and a file name.

  4. Click Save. Saving the guest's state may take some time. After the operation has finished, the VM Guest will automatically shut down.

Procedure 6.4. Restoring a VM Guest

  1. Start the Virtual Machine Manager.

  2. Type Alt+R or choose File+Restore Saved Machine.

  3. Choose the file you want to restore and proceed with Open. Once the file has been successfully loaded, the VM Guest is up and running.

6.4.2. Saving / Restoring with virsh

Save a running VM Guest with the command virsh save and specify the file to where it is saved.

Save the guest named opensuse11
virsh save opensuse11 /virtual/saves/opensuse11.vmsav
Save the guest with the ID 37
virsh save 37 /virtual/saves/opensuse11.vmsave

To restore it, use virsh restore:

virsh restore /virtual/saves/opensuse11.vmsave

6.5. Deleting a VM Guest

Deleting a VM Guest removes its XML configuration by default. Since the attached storage is not deleted by default, you will be able to use it with another VM Guest. With Virtual Machine Manager you may also delete a guest's storage files as well—this will completely erase the guest.

In order to delete a VM Guest, it has to be shut down first (refer to Section 6.3, “Changing a VM Guest's State: Start, Stop, Pause” for instructions). It is not possible to delete a running guest.

6.5.1. Deleting a VM Guest with Virtual Machine Manager

  1. In the Virtual Machine Manager, right-click a VM Guest entry.

  2. Choose Delete from the pop-up menu.

  3. A confirmation window opens. Clicking Delete will permanently erase the VM Guest. The deletion is not recoverable.

    You may also choose to permanently delete the guest's virtual disk by ticking Delete Associated Storage Files. The deletion is not recoverable either.

6.5.2. Deleting a VM Guest with virsh

To delete a VM Guest with virsh run virsh undefine VM_NAME. There is no option to automatically delete the attached storage files.

Chapter 7. Connecting and Authorizing

Having to manage several VM Host Servers, each hosting a couple of VM Guests, quickly becomes difficult to handle. One of the major benefits of libvirt is the ability to connect to several VM Host Servers at once, providing a single interface to manage all VM Guests and to connect to their graphical console.

In order to ensure only authorized users can connect, libvirt offers several connection types (via TLS, SSH, Unix sockets, and TCP) that can be combined with different authorization mechanisms (socket, PolicyKit, SASL and Kerberos).

7.1. Authentication

The power to manage VM Guests and to access their graphical console obviously is something that should be restricted to a well defined circle of persons. In order to achieve this goal, you can use the following authentication techniques on the VM Host Server:

  • Access control for UNIX sockets with permissions and group ownership. This method is available for libvirtd connections only.

  • Access control for UNIX sockets with PolicyKit. This method is available for local libvirtd connections only.

  • Username and password authentication with SASL (Simple Authentication and Security Layer). This method is available for both, libvirtd and VNC connections. Using SASL does not require real user accounts on the server, since it uses its own database to store usernames and passwords. Connections authenticated with SASL are encrypted.

  • Kerberos authentication. This method, available for libvirtd connections only, is not covered in this manual. Please refer to http://libvirt.org/auth.html#ACL_server_kerberos for details.

  • Single password authentication. This method is available for VNC connections only.

[Important]Authentication for libvirtd and VNC need to be configured separately

Access to the VM Guest management functions (via libvirtd) on the one hand and to their graphical console on the other hand, always needs to be configured separately. When restricting the access to the management tools, these restrictions do not automatically apply to VNC connections!

When accessing VM Guests from remote via TLS/SSL connections, access can be indirectly controlled on each client by restricting read permissions to the certificate's key file to a certain group. See Section 7.2.2.5, “Restricting Access (Security Considerations)” for details.

7.1.1. libvirtd Authentication

libvirtd authentication is configured in /etc/libvirt/libvirtd.conf. The configuration made here applies to all libvirt tools such as the Virtual Machine Manager or virsh.

libvirt offers two sockets: a read-only socket for monitoring purposes and a read-write socket to be used for management operations. Access to both sockets can be configured independently. By default, both sockets are owned by root.root. Default access permissions on the read-write socket are restricted to the user root (0700) and fully open on the read-only socket (0777).

In the following instructions you learn how to configure access permissions for the read-write socket. The same instructions also apply to the read-only socket. All configuration steps have to be carried out on the VM Host Server.

[Note]Default Authentication Settings on SUSE Linux Enterprise Server

The default authentication method on SUSE Linux Enterprise Server is access control for UNIX sockets. Only the user root may authenticate. When accessing the libvirt tools as a non-root user directly on the VM Host Server, you need to provide the root password through PolicyKit once and are granted access for the current and for future sessions.

Alternatively you can configure libvirt to allow system access to non-privileged users. See Section 7.3.1, “system Access for Non-Privileged Users” for details.

7.1.1.1. Access Control for UNIX Sockets with Permissions and Group Ownership

In order to grant access for non-root accounts, configure the sockets to be owned and accessible by a certain group (libvirt in the following example). This authentication method can be used for local and remote SSH connections.

  1. In case it does not exist, create the group which should own the socket:

    groupadd libvirt
    [Important]Group Needs to Exist

    The group must exist prior to restarting libvirtd. If not, the restart will fail.

  2. Add the desired users to the group:

    usermod -A libvirt tux
  3. Change the configuration in /etc/libvirt/libvirtd.conf as follows:

    unix_sock_group = "libvirt"1
           unix_sock_rw_perms = "0770"2
           auth_unix_rw = "none"3

    1

    Group ownership will be set to group libvirt.

    2

    Sets the access permissions for the socket (srwxrwx---).

    3

    Disables other authentication methods (PolicyKit or SASL). Access is solely controlled by the socket permissions.

  4. Restart libvirtd:

    rclibvirtd restart

7.1.1.2. Local Access Control for UNIX Sockets with PolicyKit

Access control for UNIX sockets with PolicyKit is the default authentication method on SUSE Linux Enterprise Server for non-remote connections. Therefore, no libvirt configuration changes are needed. With PolicyKit authorization enabled, permissions on both sockets default to 0777 and each application trying to access a socket needs to authenticate via PolicyKit. SUSE Linux Enterprise Server

[Important]PolicyKit Authentication for Local Connections Only

Authentication with PolicyKit can only be used for local connections on the VM Host Server itself, since PolicyKit does not handle remote authentication.

Two policies for accessing libvirt's sockets exist:

  • org.libvirt.unix.monitor: accessing the read-only socket

  • org.libvirt.unix.manage: accessing the read-write socket

By default, the policy for accessing the read-write socket is to authenticate with root password once and grant the privilege for the current and for future sessions (auth_admin_keep_always).

In order to grant users access to the read-write socket without having to provide the root password, there are two possibilities:

  1. Using the polkit-auth command, you can grant the privilege without any restrictions:

    polkit-auth --user tux --grant org.libvirt.unix.manage    # grant privilege
    polkit-auth --user tux --revoke org.libvirt.unix.manage   # revoke privilege
  2. Editing /etc/PolicyKit/PolicyKit.conf offers more advanced options. Add the following XML snippet in between the existing <config version="0.1"> and </config> tags:

    <match action="org.libvirt.unix.manage">1
      <match user="tux">2
        <return result="yes"/>3
      </match>
    </match>

    1

    The name of the policy; org.libvirt.unix.manage stands for accessing the read-write socket.

    2

    The username(s) which to grant the privilege. Use the | symbol to separate entries (user="tux|wilber").

    3

    The privilege that is granted. The following options exist: yes (no restrictions), no (block access completely), auth_self or auth_admin (authenticate with own password/root password every time the privilege is requested), auth_self_keep_session or auth_admin_keep_session (authenticate with own password/root password once per session) and auth_self_keep_always or auth_admin_keep_always (authenticate only once with own password/root password).

7.1.1.3. Username and Password Authentication with SASL

SASL provides username and password authentication as well as data encryption (digest-md5, by default). Since SASL maintains its own user database, the users do not need to exist on the VM Host Server. SASL is required by TCP connections and on top of TLS/SSL connections.

[Important]Plain TCP and SASL with digest-md5 Encryption

Using digest-md5 encryption on an otherwise unencrypted TCP connection does not provide enough security for production environments. It is recommended to only use it in testing environments.

[Tip]SASL Authentication on Top of TLS/SSL

Access from remote TLS/SSL connections can be indirectly controlled on the client side by restricting access to the certificate's key file. However, this might prove error-prone when dealing with a large number of clients. Utilizing SASL with TLS adds security by additionally controlling access on the server side.

To configure SASL authentication, proceed as follows:

  1. Change the configuration in /etc/libvirt/libvirtd.conf as follows:

    1. To enable SASL for TCP connections:

      auth_tcp = "sasl"
    2. To enable SASL for TLS/SSL connections:

      auth_tls = "sasl"
  2. Restart libvirtd:

    rclibvirtd restart
  3. The libvirt SASL configuration file is located at /etc/sasl2/libvirtd.conf. Normally, there is no need to change the defaults. However, if using SASL on top of TLS, you may turn off session encryption to avoid additional overhead— TLS connections are already encrypted— by commenting the mech_list. For TCP connections this parameter must be set to digest-md5:

    mech_list: digest-md5   # mandatory for TCP connections
    #mech_list: digest-md5   # apply default (username+password) TLS/SSL only!
  4. By default, no SASL users are configured, so no logins are possible. Use the following commands to add, list, and delete users:

    mercury:~ # saslpasswd2 -a libvirt tux                  # add user tux
    Password: 
    Again (for verification): 
    mercury:~ # sasldblistusers2 -f /etc/libvirt/passwd.db  # list users
    tux@mercury.example.com: userPassword
    mercury:~ # saslpasswd2 -a libvirt -d tux               # delete user tux
[Tip]virsh and SASL Authentication

When using SASL authentication you will be prompted for a username and password every time you issue a virsh command. Avoid this by using virsh in shell mode.

7.1.2. VNC Authentication

Since access to the graphical console of a VM Guest is not controlled by libvirt, but rather by QEMU, it is always necessary to additionally configure VNC authentication. The main configuration file is /etc/libvirt/qemu.conf.

Two authentication types are available: SASL and single password authentication. If you are using SASL for libvirt authentication, it is strongly recommended to use it for VNC authentication as well—it is possible to share the same database.

A third method to restrict access to the VM Guest is to enable the use of TLS encryption on the VNC server. This requires the VNC clients to have access to x509 client certificates. By restricting access to these certificates, access can indirectly be controlled on the client side. Refer to Section 7.2.2.4.2, “VNC over TLS/SSL: Client Configuration” for details.

7.1.2.1. Username and Password Authentication with SASL

SASL provides username and password authentication as well as data encryption. Since SASL maintains its own user database, the users do not need to exist on the VM Host Server. As with SASL authentication for libvirt, you may use SASL on top of TLS/SSL connections. Refer to Section 7.2.2.4.2, “VNC over TLS/SSL: Client Configuration” for details on configuring these connections.

To configure SASL authentication for VNC, proceed as follows:

  1. Create a SASL configuration file. It is recommended to use the existing libvirt file. If you have already configured SASL for libvirt and are planning to use the same settings including the same username/password database, a simple link is suitable:

    ln -s /etc/sasl2/libvirt.conf /etc/sasl2/qemu.conf

    In case you are setting up SASL for VNC only or planning to use a different configuration than for libvirt, copy the existing file to use as a template and edit it according to your needs:

    cp /etc/sasl2/libvirt.conf /etc/sasl2/qemu.conf
  2. By default, no SASL users are configured, so no logins are possible. Use the following commands to add, list, and delete users:

    mercury:~ # saslpasswd2 -a libvirt tux                  # add user tux
    Password: 
    Again (for verification): 
    mercury:~ # sasldblistusers2 -f /etc/libvirt/passwd.db  # list users
    tux@mercury.example.com: userPassword
    mercury:~ # saslpasswd2 -a libvirt -d tux               # delete user tux
  3. Change the configuration in /etc/libvirt/qemu.conf as follows:

    vnc_listen = "0.0.0.0"
    vnc_sasl = 1

    The first parameter enables VNC to listen on all public interfaces (rather than to the local host only), and the second parameter enables SASL authentication.

  4. Restart libvirtd:

    rclibvirtd restart
  5. Restart all VM Guests that have been running prior to changing the configuration. VM Guests that have not been restarted will not use SASL authentication for VNC connects.

[Note]Supported VNC Viewers

Currently only the same VNC viewers that also support TLS/SSL connections, support SASL authentication, namely Virtual Machine Manager, virt-viewer, and vinagre.

7.1.2.2. Single Password Authentication

Access to the VNC server may also be controlled by setting a VNC password. You can either set a global password for all VM Guests or set individual passwords for each guest. The latter requires to edit the VM Guest's config files.

[Note]Always Set a Global Password

If you are using the single password authentication, it is good practice to set a global password even if setting passwords for each VM Guest. This will always leave your virtual machines protected with a fallback password if you forget to set a per-machine password. The global password will only be used if no other password is set for the machine.

Procedure 7.1. Setting a Global VNC Password

  1. Change the configuration in /etc/libvirt/qemu.conf as follows:

    vnc_listen = "0.0.0.0"
           vnc_password = "PASSWORD"

    The first parameter enables VNC to listen on all public interfaces (rather than to the local host only), and the second parameter sets the password. The maximum length of the password is eight characters.

  2. Restart libvirtd:

    rclibvirtd restart
  3. Restart all VM Guests that have been running prior to changing the configuration. VM Guests that have not been restarted will not use password authentication for VNC connects.

Procedure 7.2. Setting a VM Guest Specific VNC Password

  1. Change the configuration in /etc/libvirt/qemu.conf as follows to enable VNC to listen on all public interfaces (rather than to the local host only).

    vnc_listen = "0.0.0.0"
  2. Open the VM Guest's XML configuration file in an editor. Replace VM NAME in the following example with the name of the VM Guest. The editor that is used defaults to $EDITOR. If that variable is not set, vi is used.

    virsh edit VM NAME
  3. Search for the element <graphics> with the attribute type='vnc', for example:

    <graphics type='vnc' port='-1' autoport='yes'/>
  4. Add the passwd=PASSWORD attribute, save the file and leave the editor. The maximum length of the password is eight characters.

    <graphics type='vnc' port='-1' autoport='yes' passwd='PASSWORD'/>
  5. Restart libvirtd:

    rclibvirtd restart
  6. Restart all VM Guests that have been running prior to changing the configuration. VM Guests that have not been restarted will not use password authentication for VNC connects.

[Warning]Security

The VNC protocol is not considered to be safe. Although the password is sent encrypted, it might be vulnerable, when an attacker is able to sniff both, the encrypted password and the encryption key. Therefore, it is recommended to use VNC with TLS/SSL or tunneled over SSH. virt-viewer, as well as the Virtual Machine Manager and vinagre from version 2.30 on, support both methods.

7.2. Configuring Remote Connections

A major benefit of libvirt is the ability to manage VM Guests on different remote hosts from a central location. This section gives detailed instructions on how to configure server and client to allow remote connections.

7.2.1. Remote Tunnel over SSH (qemu+ssh)

Enabling a remote connection that is tunneled over SSH on the VM Host Server only requires the ability to accept SSH connections. Make sure the SSH daemon is started (rcsshd status) and that the ports for service SSH are opened in the firewall.

User authentication for SSH connections can be done using traditional file user/group ownership and permissions as described in Section 7.1.1.1, “Access Control for UNIX Sockets with Permissions and Group Ownership”. Connecting as user tux (qemu+ssh://tuxsIVname;/system) works out of the box and does not require additional configuration on the libvirt side.

When connecting via SSH qemu+ssh://USER@SYSTEM you need to provide the password for USER. This can be avoided by copying your public key to ~USER/.ssh/authorized_keys on the VM Host Server as explained in Section “Copying an SSH Key” (Chapter 14, SSH: Secure Network Operations, ↑Security Guide). Using an ssh-agent on the machine from which you are connecting adds even more convenience—see Section “Using the ssh-agent” (Chapter 14, SSH: Secure Network Operations, ↑Security Guide) for instructions.

7.2.2. Remote TLS/SSL Connection with x509 Certificate (qemu+tls)

Using TCP connections with TLS/SSL encryption and authentication via x509 certificates is much more complicated to set up than SSH, but it is a lot more scalable. Use this method if you have to manage several VM Host Servers with a varying number of administrators.

7.2.2.1. Basic concept

Basically, TLS (Transport Layer Security) encrypts the communication between two computers by using certificates. The computer starting the connection is always considered as the client using a client certificate, while the receiving computer is always considered as the server, using a server certificate. This scenario applies, for example, if you manage your VM Host Servers from a central desktop.

If connections are initiated from both computers, each needs to have a client and a server certificate. This is the case, for example, if you migrate a VM Guest from one host to another.

Each x509 certificate has a matching private key file. Only the combination of certificate and private key file is able to identify itself correctly. In order to assure that a certificate was issued by the assumed owner, it is signed and issued by a central certificate called certificate authority (CA). Both the client and the server certificates must be issued by the same CA.

[Important]User Authentication

Using a remote TLS/SSL connection basically only ensures that two computers are allowed to communicate in a certain direction. Restricting access to certain users can indirectly be achieved on the client side by restricting access to the certificates. Refer to Section 7.2.2.5, “Restricting Access (Security Considerations)” for details. libvirt also supports user authentication on the server with SASL. Read more in Section 7.2.2.6, “Central User Authentication with SASL for TLS Sockets”.

7.2.2.2. Configuring the VM Host Server

The VM Host Server is the machine receiving connections. Therefore, the server certificates have to be installed. The CA certificate needs to be installed, as well. Once the certificates are in place, TLS support can be turned on for libvirt.

  1. Create the server certificate and export it together with the CA certificate as described in Section A.2, “Generating x509 Client/Server Certificates”.

  2. Create the following directories on the VM Host Server:

    mkdir -p /etc/pki/CA/ /etc/pki/libvirt/private/

    Install the certificates as follows:

    /etc/pki/CA/cacert.pem
    /etc/pki/libvirt/servercert.pem
    /etc/pki/libvirt/private/serverkey.pem
    [Important]Restrict Access to Certificates

    Make sure to restrict access to certificates as explained in Section 7.2.2.5, “Restricting Access (Security Considerations)”.

  3. Enable TLS support by editing /etc/libvirt/libvirtd.conf and setting listen_tls = 1. Restart libvirtd:

    rclibvirtd restart
  4. By default, libvirt uses the TCP port 16514 for accepting secure TLS connections. Open this port in the firewall.

[Important]Restarting libvirtd with TLS enabled

If you enable TLS for libvirt, the server certificates need to be in place, otherwise restarting libvirtd will fail. You also need to restart libvirtd in case you change the certificates.

7.2.2.3. Configuring the Client and Testing the Setup

The client is the machine initiating connections. Therefore the client certificates have to be installed. The CA certificate needs to be installed, as well.

  1. Create the client certificate and export it together with the CA certificate as described in Section A.2, “Generating x509 Client/Server Certificates”.

  2. Create the following directories on the client:

    mkdir -p /etc/pki/CA/ /etc/pki/libvirt/private/

    Install the certificates as follows:

    /etc/pki/CA/cacert.pem
    /etc/pki/libvirt/clientcert.pem
    /etc/pki/libvirt/private/clientkey.pem
    [Important]Restrict Access to Certificates

    Make sure to restrict access to certificates as explained in Section 7.2.2.5, “Restricting Access (Security Considerations)”.

  3. Test the client/server setup by issuing the following command. Replace mercury.example.com with the name of your VM Host Server. Specify the same full qualified hostname as used when creating the server certificate.

    virsh -c qemu+tls://mercury.example.com/system list --all

    If your setup is correct, you will see a list of all VM Guests registered with libvirt on the VM Host Server.

7.2.2.4. Enabling VNC for TLS/SSL connections

Currently, VNC communication over TLS is only supported by few tools. The widespread tightvnc or tigervnc viewer, for example, do not support TLS. Known to work are the Virtual Machine Manager (virt-manager), virt-viewer and the GNOME VNC viewer vinagre.

7.2.2.4.1. VNC over TLS/SSL: VM Host Server Configuration

In order to access the graphical console via VNC over TLS/SSL, you need to configure the VM Host Server as follows:

  1. Open ports for the service VNC in your firewall.

  2. Create a directory /etc/pki/libvirt-vnc and link the certificates into this directory as follows:

    mkdir -p /etc/pki/libvirt-vnc && cd /etc/pki/libvirt-vnc
    	ln -s /etc/pki/CA/cacert.pem ca-cert.pem
    	ln -s /etc/pki/libvirt/servercert.pem server-cert.pem
    	ln -s /etc/pki/libvirt/private/serverkey.pem server-key.pem
  3. Edit /etc/libvirt/qemu.conf and set the following parameters:

    vnc_listen = "0.0.0.0"
    	vnc_tls = 1
    	vnc_tls_x509_verify = 1
  4. Restart the libvirtd:

    rclibvirtd restart
    [Important]VM Guests Need to be Restarted

    The VNC TLS setting is only set when starting a VM Guest. Therefore, you need to restart all machines that have been running prior to making the configuration change.

7.2.2.4.2. VNC over TLS/SSL: Client Configuration

The only action needed on the client side is to place the x509 client certificates in a location recognized by the client of choice. Unfortunately, each supported client—Virtual Machine Manager, virt-viewer, and vinagre—expects the certificates in a different location. However, Virtual Machine Manager and vinagre can either read from a system-wide location applying to all users, or from a per user location.

Virtual Machine Manager (virt-manager)

In order to connect to the remote host, Virtual Machine Manager requires the setup explained in Section 7.2.2.3, “Configuring the Client and Testing the Setup”. In order to be able to connect via VNC the client certificates also need to be placed in the following locations:

System wide location
/etc/pki/CA/cacert.pem
/etc/pki/libvirt-vnc/clientcert.pem
/etc/pki/libvirt-vnc/private/clientkey.pem
Per user location
/etc/pki/CA/cacert.pem
~/.pki/libvirt-vnc/clientcert.pem
~/.pki/libvirt-vnc/private/clientkey.pem
virt-viewer

virt-viewer only accepts certificates from a system wide location:

/etc/pki/CA/cacert.pem
/etc/pki/libvirt-vnc/clientcert.pem
/etc/pki/libvirt-vnc/private/clientkey.pem
vinagre
System wide location
/etc/pki/CA/cacert.pem
/etc/pki/vinagre/clientcert.pem
/etc/pki/vinagre/private/clientkey.pem
Per user location
$HOME/.pki/CA/cacert.pem
~/.pki/vinagre/clientcert.pem
~/.pki/vinagre/private/clientkey.pem
[Important]Restrict Access to Certificates

Make sure to restrict access to certificates as explained in Section 7.2.2.5, “Restricting Access (Security Considerations)”.

7.2.2.5. Restricting Access (Security Considerations)

Each x509 certificate consists of two pieces: the public certificate and a private key. A client can only authenticate using both pieces. Therefore, any user that has read access to the client certificate and its private key can access your VM Host Server. On the other hand, an arbitrary machine equipped with the full server certificate can pretend to be the VM Host Server. Since this is probably not desirable, access to at least the private key files needs to be restricted as much as possible. The easiest way to control access to a key file is to use access permissions.

Server Certificates

Server certificates need to be readable for QEMU processes. On SUSE Linux Enterprise Server QEMU processes started from libvirt tools are owned by root, so it is sufficient if root is able to read them certificates:

chmod 700 /etc/pki/libvirt/private/
chmod 600 /etc/pki/libvirt/private/serverkey.pem

If you change the ownership for QEMU processes in /etc/libvirt/qemu.conf, you also need to adjust the ownership of the key file.

System Wide Client Certificates

To control access to a key file that is available system wide, restrict read access a certain group, so that only members of that group can read the key file. In the following example, a group libvirt is created and the group ownership of the clientkey.pem and its parent directory is set to libvirt. Afterwards, the access permissions are restricted to owner and group. Finally the user tux is added to the group libvirt, so he will be able to access the key file.

CERTPATH="/etc/pki/libvirt/"
# create group libvirt
groupadd libvirt
# change ownership to user root and group libvirt
chown root.libvirt $CERTPATH/private $CERTPATH/clientkey.pem
# restrict permissions
chmod 750 $CERTPATH/private
chmod 640 $CERTPATH/private/clientkey.pem
# add user tux to group libvirt
usermod -A libvirt tux
Per User Certificates

User specific client certificates for accessing the graphical console of a VM Guest via VNC need to be placed in the users home directory in ~/.pki. Contrary to, for example, the VNC viewer using these certificates do not check the access permissions of the private key file. Therefore, it is solely on the user's responsibility to make sure the key file is not readable by others.

7.2.2.5.1. Restricting Access from the Server Side

By default, every client that is equipped with appropriate client certificates may connect to a VM Host Server accepting TLS connections. Therefore, it is possible to use additional server side authentication with SASL as described in Section 7.1.1.3, “Username and Password Authentication with SASL”.

It is also possible to restrict access with a whitelist of DNs (distinguished names), so only clients with a certificate matching a DN from the list can connect.

Add a list of allowed DNs to tls_allowed_dn_list in /etc/libvirt/libvirtd.conf. This list may contain wild cards. Do not specify an empty list, since that would result in refusing all connections.

tls_allowed_dn_list = [
   "C=US,L=Provo,O=SUSE Linux Products GmbH,OU=*,CN=venus.example.com,EMAIL=*",
   "C=DE,L=Nuremberg,O=SUSE Linux Products GmbH,OU=Documentation,CN=*"]

Get the distinguished name of a certificate with the following command:

certtool -i --infile /etc/pki/libvirt/clientcert.pem | grep "Subject:"

Restart libvirtd after having changed the configuration:

rclibvirtd restart

7.2.2.6. Central User Authentication with SASL for TLS Sockets

A direct user authentication via TLS is not possible - this is handled indirectly on each client via the read permissions for the certificates as explained in Section 7.2.2.5, “Restricting Access (Security Considerations)”. However, if a central, server based user authentication is needed libvirt also allows to use SASL (Simple Authentication and Security Layer) on top of TLS for direct user authentication. See Section 7.1.1.3, “Username and Password Authentication with SASL” for configuration details.

7.2.2.7. Troubleshooting

7.2.2.7.1. Virtual Machine Manager/virsh Cannot Connect to Server

Check the following in the given order:

Is it a firewall issue (TCP port 16514 needs to be open on the server)?
Is the client certificate (certificate and key) readable by the user that has started Virtual Machine Manager/virsh?
Has the same full qualified hostname as in the server certificate been specified with the connection?
Is TLS enabled on the server (listen_tls = 1)?
Has libvirtd been restarted on the server?
7.2.2.7.2. VNC Connection fails

Ensure that you can basically connect to the remote server using Virtual Machine Manager. If so, check whether the virtual machine on the server has been started with TLS support. The virtual machine's name in the following example is sles11.

ps ax | grep qemu | grep "\-name sles11" | awk -F" -vnc " '{ print FS $2 }'

If the output does not begin with a string similar to the following, the machine has not been started with TLS support and must be restarted.

 -vnc 0.0.0.0:0,tls,x509verify=/etc/pki/libvirt

7.3. Connecting to a VM Host Server

In order to connect to a hypervisor with libvirt, you need to specify a uniform resource identifier (URI). This URI is needed with virsh and virt-viewer (except when working as root on the VM Host Server) and is optional for the Virtual Machine Manager. Although the latter can be called with a connection parameter (for example, virt-manager -c qemu:///system), it also offers a graphical interface to create connection URIs. See Section 7.3.2, “Managing Connections with Virtual Machine Manager” for details.

HYPERVISOR1+PROTOCOL2://USER@REMOTE3/CONNECTION_TYPE4

1

Specify the hypervisor. SUSE Linux Enterprise Server currently supports the following hypervisors: test (dummy for testing), qemu (KVM), and xen (Xen). This parameter is mandatory.

2

When connecting to a remote host, specify the protocol here. Can be one of: ssh (connection via SSH tunnel), tcp (TCP connection with SASL/Kerberos authentication), tls (TLS/SSL encrypted connection with authentication via x509 certificates).

3

When connecting to a remote host, specify the user and the remote hostname. If no user is specified, the username that has called the command ($USER) is used. Please see below for more information. For TLS connections the hostname has to be specified exactly as in the x509 certificate.

4

When connecting to QEMU hypervisor, two connections types are accepted: system for full access rights, or session for restricted access. Since session access is not supported on SUSE Linux Enterprise Server, this documentation focuses on system access.

Example Hypervisor Connection URIs

test:///default

Connect to the local dummy hypervisor. Useful for testing.

qemu:///system

Connect to the QEMU hypervisor on the local host having full access (type system).

qemu+ssh://tux@mercury.example.com/system

Connect to the QEMU hypervisor on the remote host mercury.example.com. The connection is established via an SSH tunnel.

qemu+tls://saturn.example.com/system

Connect to the QEMU hypervisor on the remote host mercury.example.com. The connection is established TLS/SSL.

For more details and examples, refer to the libvirt documentation at http://libvirt.org/uri.html.

[Note]Usernames in URIs

A username needs to be specified when using Unix socket authentication (regardless whether using the username/password authentication scheme or PolicyKit). This applies to all SSH and local connections.

There is no need to specify a username when using SASL authentication (for TCP or TLS connections) or when doing no additional server side authentication for TLS connections. With SASL the username will not be evaluated—you will be prompted for a SASL user/password combination in any case.

7.3.1. system Access for Non-Privileged Users

As mentioned above, a connection to the QEMU hypervisor can be established using two different protocols: session and system. A session connection is spawned with the same privileges as the client program. Such a connection is intended for desktop virtualization, since it is restricted (for example no USB/PCI device assignments, no virtual network setup, limited remote access to libvirtd).

The system connection intended for server virtualization has no functional restrictions but is, by default, only accessible by root. However, with the addition of the DAC (Discretionary Access Control) driver to libvirt it is now possible to grant non-privileged users system access. To grant system access to the user tux, proceed as follows:

Procedure 7.3. Granting system Access to a Regular User

  1. Enable access via UNIX sockets as described in Section 7.1.1.1, “Access Control for UNIX Sockets with Permissions and Group Ownership”. In that example access to libvirt is granted to all members of the group libvirt and tux is made a member of this group. This ensures that tux can connect using virsh or Virtual Machine Manager.

  2. Edit /etc/libvirt/qemu.conf and change the configuration as follows:

    user = "tux"
    group = "libvirt"
    dynamic_ownership = 1

    This ensures that the VM Guests are started by tux and that resources bound to the guest (for example virtual disks) can be accessed and modified by tux.

  3. Make tux a member of the group kvm:

    usermod -A kvm tux

    This step is needed to grant access to /dev/kvm which is required to start VM Guests.

  4. Restart libvirtd:

    rclibvirtd restart

7.3.2. Managing Connections with Virtual Machine Manager

The Virtual Machine Manager uses a Connection for every VM Host Server it manages. Each connection contains all VM Guests on the respective host. By default, a connection to the localhost is already configured and connected.

All configured connections are displayed in the Virtual Machine Manager main window. Active connections are marked with a small triangle which you can click in order to fold or unfold the list of VM Guests for this connection.

Inactive connections are listed gray and are marked with Not Connected. Either double-click or right-click it and choose Connect from the context menu. You can also Delete an existing connection from this menu.

[Note]Editing Existing Connections

It is not possible to edit an existing connection. In order to change a connection, create a new one with the desired parameters and delete the old one.

To add a new connection in the Virtual Machine Manager, proceed as follows:

  1. Choose File+Add Connection

  2. Choose the host's Hypervisor (Xen or QEMU/KVM)

  3. Choose a Connection type—either Local for connecting to the host the Virtual Machine Manager was started on, or one of the remote connections (see Section 7.2, “Configuring Remote Connections” for more information).

  4. In case of a remote connection, enter the Hostname of the remote machine as USERNAME@REMOTE_HOST. Usernames must be specified for local connections as well as for SSH

    [Important]Specifying a Username

    There is no need to specify a username for TCP and TLS connections; it will not be evaluated anyway. A username must be specified for local connections as well as for SSH connections—if not, the default user root will be used.

  5. If you do not want the connection to be automatically activated when starting the Virtual Machine Manager, remove the tick from Autoconnect.

  6. Finish the configuration by clicking Connect.

Chapter 8. Managing Storage

When managing a VM Guest on the VM Host Server itself, it is possible to access the complete file system of the VM Host Server in order to attach or create virtual hard disks or to attach existing images to the VM Guest. However, this is not possible when managing VM Guests from a remote host. For this reason, libvirt supports so called Storage Pools which can be accessed from remote machines.

[Tip]CD/DVD ISO images

In order to be able to access CD/DVD iso images on the VM Host Server from remote, they also need to be placed in a storage pool.

libvirt knows two different types of storage: volumes and pools.

Storage Volume

A storage volume is a storage device that can be assigned to a guest—a virtual disk or a CD/DVD/floppy image. Physically (on the VM Host Server) it can be a block device (a partition, a logical volume, etc.) or a file.

Storage Pool

A storage pool basically is a storage resource on the VM Host Server that can be used for storing volumes, similar to network storage for a desktop machine. Physically it can be one of the following types:

File System Directory (dir)

A directory for hosting image files. The files can be either one of the supported disk formats (raw, qcow2, or qed), or ISO images.

Physical Disk Device (disk)

Use a complete physical disk as storage. A partition is created for each volume that is added to the pool.

Pre-Formatted Block Device (fs)

Specify a partition to be used in the same way as a file system directory pool (a directory for hosting image files). The only difference to using a file system directory is the fact that libvirt takes care of mounting the device.

iSCSI Target (iscsi)

Set up a pool on an iSCSI target. You need to have been logged into the volume once before, in order to use it with libvirt (use the YaST iSCSI Initiator to detect and log in to a volume, see Storage Administration Guide (↑Storage Administration Guide) for details). Volume creation on iSCSI pools is not supported, instead each existing Logical Unit Number (LUN) represents a volume. Each volume/LUN also needs a valid (empty) partition table or disk label before you can use it. If missing, use fdisk to add it:

~ # fdisk -cu /dev/disk/by-path/ip-192.168.2.100:3260-iscsi-iqn.2010-10.com.example:[...]-lun-2
Device contains neither a valid DOS partition table, nor Sun, SGI
or OSF disklabel
Building a new DOS disklabel with disk identifier 0xc15cdc4e.
Changes will remain in memory only, until you decide to write them.
After that, of course, the previous content won't be recoverable.

Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.
Syncing disks.
	
LVM Volume Group (logical)

Use a LVM volume group as a pool. You may either use a pre-defined volume group, or create a group by specifying the devices to use. Storage volumes are created as partitions on the volume.

[Warning]Deleting the LVM Based Pool

When the LVM based pool is deleted in the Storage Manager, the volume group is deleted as well. This results in a non-recoverable loss of all data stored on the pool!

Multipath Devices (mpath)

At the moment, multipathing support is limited to assigning existing devices to the guests. Volume creation or configuring multipathing from within libvirt is not supported.

Network Exported Directory (netfs)

Specify a network directory to be used in the same way as a file system directory pool (a directory for hosting image files). The only difference to using a file system directory is the fact that libvirt takes care of mounting the directory. Supported protocols are NFS and glusterfs.

SCSI Host Adapter (scsi)

Use an SCSI host adapter in almost the same way a an iSCSI target. It is recommended to use a device name from /dev/disk/by-* rather than the simple /dev/sdX, since the latter may change (for example when adding or removing hard disks). Volume creation on iSCSI pools is not supported, instead each existing LUN (Logical Unit Number) represents a volume.

[Warning]Security Considerations

In order to avoid data loss or data corruption, do not attempt to use resources such as LVM volume groups, iSCSI targets, etc. that are used to build storage pools on the VM Host Server, as well. There is no need to connect to these resources from the VM Host Server or to mount them on the VM Host Server—libvirt takes care of this.

Do not mount partitions on the VM Host Server by label. Under certain circumstances it is possible that a partition is labeled from within a VM Guest with a name already existing on the VM Host Server.

8.1. Managing Storage with Virtual Machine Manager

The Virtual Machine Manager provides a graphical interface—the Storage Manager— to manage storage volumes and pools. To access it, either right-click a connection and choose Details, or highlight a connection and choose Edit+Connection Details. Select the Storage tab.

8.1.1. Adding a Storage Pool

To add a storage pool, proceed as follows:

  1. Click the plus symbol in the bottom left corner to open the Add a New Storage Pool Window.

  2. Provide a Name for the pool (consisting of alphanumeric characters plus _-.) and select a Type. Proceed with Forward.

  3. Specify the needed details in the following window. The data that needs to be entered depends on the type of pool you are creating.

    Typedir:
    • Target Path: Specify an existing directory.

    Typedisk:
    • Target Path: The directory which hosts the devices. The default value /dev should fit in most cases.

    • Format: Format of the device's partition table. Using auto should work in most cases. If not, get the needed format by running the command parted -l on the VM Host Server.

    • Source Path: Path to the device. It is recommended to use a device name from /dev/disk/by-* rather than the simple /dev/sdX, since the latter may change (for example when adding or removing hard disks). You need to specify the path that resembles the whole disk, not a partition on the disk (if existing).

    • Build Pool: Activating this option formats the device. Use with care— all data on the device will be lost!

    Typefs:
    • Target Path: Mount point on the VM Host Server file system.

    • Format: File system format of the device. the default value auto should work.

    • Source Path: Path to the device file. It is recommended to use a device name from /dev/disk/by-* rather than the simple /dev/sdX, since the latter may change (for example when adding or removing hard disks).

    Typeiscsi:

    Get the necessary data by running the following command on the VM Host Server:

    iscsiadm --mode node

    It will return a list of iSCSI volumes with the following format. The elements highlighted with a bold font are the ones needed:

    IP_ADDRESS:PORT,TPGT TARGET_NAME_(IQN)
    • Target Path: The directory containing the device file. Use /dev/disk/by-path (default) or /dev/disk/by-id.

    • Host Name: Host name or IP address of the iSCSI server.

    • Source Path: The iSCSI target name (IQN).

    Typelogical:
    • Target Path: In case you use an existing volume group, specify the existing device path. In case of building a new LVM volume group, specify a device name in the /dev directory that does not already exist.

    • Source Path: Leave empty when using an existing volume group. When creating a new one, specify its devices here.

    • Build Pool: Only activate when creating a new volume group.

    Typempath:
    • Target Path: Support of multipathing is currently limited to making all multipath devices available. Therefore you may enter an arbitrary string here (needed, otherwise the XML parser will fail), it will be ignored anyway.

    Typenetfs:
    • target Path: Mount point on the VM Host Server file system.

    • Format: Network file system protocol

    • Host Name: IP address or hostname of the server exporting the network file system.

    • Source Path: Directory on the server that is being exported.

    Typescsi:
    • Target Path: The directory containing the device file. Use /dev/disk/by-path (default) or /dev/disk/by-id.

    • Source Path: Name of the SCSI adapter.

    [Note]File Browsing

    Using the file browser by clicking on Browse is not possible when operating from remote.

  4. Click Finish to add the storage pool.

8.1.2. Managing Storage Pools

Virtual Machine Manager's Storage Manager lets you create or delete volumes in a pool. You may also temporarily deactivate or permanently delete existing storage pools. Changing the basic configuration of a pool is currently not supported by SUSE.

8.1.2.1. Starting, Stopping and Deleting Pools

The purpose of storage pools is to provide block devices located on the VM Host Server, that can be added to a VM Guest when managing it from remote. In order to make a pool temporarily inaccessible from remote, you may Stop it by clicking on the stop symbol in the bottom left corner of the Storage Manager. Stopped pools are marked with State: Inactive and are grayed out in the list pane. By default, a newly created pool will be automatically started On Boot of the VM Host Server.

To Start an inactive pool and make it available from remote again click on the play symbol in the bottom left corner of the Storage Manager.

[Note]A Pool's State Does not Affect Attached Volumes

Volumes from a pool attached to VM Guests are always available, regardless of the pool's state (Active (stopped) or Inactive (started)). The state of the pool solely affects the ability to attach volumes to a VM Guest via remote management.

To permanently make a pool inaccessible, you can Delete it by clicking on the shredder symbol in the bottom left corner of the Storage Manager. You may only delete inactive pools. Deleting a pool does not physically erase its contents on VM Host Server—it only deletes the pool configuration. However, you need to be extra careful when deleting pools, especially when deleting LVM volume group-based tools:

[Warning]Deleting Storage Pools

Deleting storage pools based on local file system directories, local partitions or disks has no effect on the availability of volumes from these pools currently attached to VM Guests.

Volumes located in pools of type iSCSI, SCSI, LVM group or Network Exported Directory will become inaccessible from the VM Guest in case the pool will be deleted. Although the volumes themselves will not be deleted, the VM Host Server will no longer have access to the resources.

Volumes on iSCSI/SCSI targets or Network Exported Directory will be accessible again when creating an adequate new pool or when mounting/accessing these resources directly from the host system.

When deleting an LVM group-based storage pool, the LVM group definition will be erased and the LVM group will no longer exist on the host system. The configuration is not recoverable and all volumes from this pool are lost.

8.1.2.2. Adding Volumes to a Storage Pool

Virtual Machine Manager lets you create volumes in all storage pools, except in pools of types Multipath, iSCSI, or SCSI. A volume in these pools is equivalent to a LUN and cannot be changed from within libvirt.

  1. A new volume can either be created using the Storage Manager or while adding a new storage device to a VM Guest. In both cases, select a Storage Pool and then click New Volume.

  2. Specify a Name for the image and choose an image format (note that SUSE currently only supports raw, qcow2, or qed images). The latter option is not available on LVM group-based pools.

    Specify a Max Capacity and the amount of space that should initially be allocated. If both values differ, a sparse image file, growing on demand, will be created.

  3. Start the volume creation by clicking Finish.

8.1.2.3. Deleting Volumes From a Storage Pool

Deleting a volume can only be done from the Storage Manager, by selecting a volume and clicking Delete Volume. Confirm with Yes. Use this function with extreme care!

[Warning]No Checks Upon Volume Deletion

A volume will be deleted in any case, regardless whether it is currently used in an active or inactive VM Guest. There is no way to recover a deleted volume.

Whether a volume is used by a VM Guest is indicated in the Used By column in the Storage Manager.

8.2. Managing Storage with virsh

Managing storage from the command line is also possible by using virsh. However, creating storage pools is currently not supported by SUSE. Therefore this section is restricted to document functions like starting, stopping and deleting pools and volume management.

A list of all virsh subcommands for managing pools and volumes is available by running virsh help pool and virsh help volume, respectively.

8.2.1. Listing Pools and Volumes

List all pools currently active by executing the following command. To also list inactive pools, add the option --all:

virsh pool-list --details

Details about a specific pool can be obtained with the pool-info subcommand:

virsh pool-info POOL

Volumes can only be listed per pool by default. To list all volumes from a pool, enter the following command.

virsh vol-list --details POOL

At the moment virsh offers no tools to show whether a volume is used by a guest or not. The following procedure describes a way to list volumes from all pools that are currently used by a VM Guest.

Procedure 8.1. Listing all Storage Volumes Currently Used on a VM Host Server

  1. Create an XSLT style sheet by saving the following content to a file, for example, ~/libvirt/guest_storage_list.xsl:

    <?xml version="1.0" encoding="UTF-8"?>
    <xsl:stylesheet version="1.0"
      xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
      <xsl:output method="text"/>
      <xsl:template match="text()"/>
      <xsl:strip-space elements="*"/>
      <xsl:template match="disk">
        <xsl:text>  </xsl:text>
        <xsl:value-of select="(source/@file|source/@dev|source/@dir)[1]"/>
        <xsl:text>&#10;</xsl:text>
      </xsl:template>
    </xsl:stylesheet>
  2. Run the following commands in a shell. It is assumed that the guest's XML definitions are all stored in the default location (/etc/libvirt/qemu). xsltproc is provided by the package libxslt.

    SSHEET="$HOME/libvirt/guest_storage_list.xsl"
    cd /etc/libvirt/qemu
    for FILE in *.xml; do
      basename $FILE .xml 
      xsltproc $SSHEET $FILE
    done

8.2.2. Starting, Stopping and Deleting Pools

Use the virsh pool subcommands to start, stop or delete a pool. Replace POOL with the pool's name or its UUID in the following examples:

Stopping a Pool
virsh pool-destroy POOL
[Note]A Pool's State Does not Affect Attached Volumes

Volumes from a pool attached to VM Guests are always available, regardless of the pool's state (Active (stopped) or Inactive (started)). The state of the pool solely affects the ability to attach volumes to a VM Guest via remote management.

Deleting a Pool
virsh pool-delete POOL
[Warning]Deleting Storage Pools

Deleting storage pools based on local file system directories, local partitions or disks has no effect on the availability of volumes from these pools currently attached to VM Guests.

Volumes located in pools of type iSCSI, SCSI, LVM group or Network Exported Directory will become inaccessible from the VM Guest in case the pool will be deleted. Although the volumes themselves will not be deleted, the VM Host Server will no longer have access to the resources.

Volumes on iSCSI/SCSI targets or Network Exported Directory will be accessible again when creating an adequate new pool or when mounting/accessing these resources directly from the host system.

When deleting an LVM group-based storage pool, the LVM group definition will be erased and the LVM group will no longer exist on the host system. The configuration is not recoverable and all volumes from this pool are lost.

Starting a Pool
virsh pool-start POOL
Enable Autostarting a Pool
virsh pool-autostart POOL

Only pools that are marked to autostart start will automatically be started in case the VM Host Server reboots.

Disable Autostarting a Pool
virsh pool-autostart POOL --disable

8.2.3. Adding Volumes to a Storage Pool

virsh offers two ways to create storage pools: either from an XML definition with vol-create and vol-create-from or via command line arguments with vol-create-as. The first two methods are currently not supported by SUSE, therefore this section focuses on the subcommand vol-create-as.

To add a volume to an existing pool, enter the following command:

virsh vol-create-as POOL1NAME2 12G --format3raw|qcow2|qed4 --allocation 4G5

1

Name of the pool to which the volume should be added

2

Name of the volume

3

Size of the image, in this example 12 gigabyte. Use the suffixes k,M,G,T for kilobyte, megabyte, gigabyte, and terabyte, respectively.

4

Format of the volume. SUSE currently supports raw, qcow2, and qed.

5

Optional parameter. By default virsh creates a sparse image file that grows on demand. Specify the amount of space that should be allocated with this parameter (4 gigabyte in this example). Use the suffixes k,M,G,T for kilobyte, megabyte, gigabyte, and terabyte, respectively.

When not specifying this parameter, a sparse image file with no allocation will be generated. If you want to create a non-sparse volume, specify the whole image size with this parameter (would be 12G in this example).

8.2.3.1. Cloning Existing Volumes

Another way to add volumes to a pool is to clone an existing volume. The new instance is always created in the same pool as the original.

vol-clone NAME_EXISTING_VOLUME1NAME_NEW_VOLUME2 --pool POOL3

1

Name of the existing volume that should be cloned

2

Name of the new volume

3

Optional parameter. libvirt tries to locate the existing volume automatically. If that fails, specify this parameter.

8.2.4. Deleting Volumes from a Storage Pool

To permanently delete a volume from a pool, use the subcommand vol-delete:

virsh vol-delete NAME --pool POOL

--pool is optional. libvirt tries to locate the volume automatically. If that fails, specify this parameter.

[Warning]No Checks Upon Volume Deletion

A volume will be deleted in any case, regardless whether it is currently used in an active or inactive VM Guest. There is no way to recover a deleted volume.

Whether a volume is used by a VM Guest can only be detected by using by the method described in Procedure 8.1, “Listing all Storage Volumes Currently Used on a VM Host Server”.

8.3. Locking Disk Files and Block Devices with virtlockd

Locking block devices and disk files prevents concurrent writes to these resources from different VM Guests. It provides protection against starting the same VM Guest twice, or adding the same disk to two different virtual machines. This will reduce the risk of a virtual machine's disk image becoming corrupted as a result of a wrong configuration.

The locking is controlled by a daemon called virtlockd. Since it operates independently from the libvirtd daemon, locks will endure a crash or a restart of libvirtd. Locks will even persist in the case of an update of the virtlockd itself, since it has the ability to re-execute itself. This ensures that VM Guests do not have to be restarted upon a virtlockd update.

8.3.1. Enable Locking

Locking virtual disks is not enabled by default on SUSE Linux Enterprise Server. To enable and automatically start it upon rebooting, perform the following steps:

  1. Edit /etc/libvirt/qemu.conf and set

    lock_manager = "lockd"
  2. Start the virtlockd daemon with the following command:

    rcvirtlockd start
  3. Restart the libvirtd daemon with:

    rclibvirtd restart
  4. Make sure virtlockd is automatically started when booting the system:

    insserv virtlockd

8.3.2. Configure Locking

By default virtlockd is configured to automatically lock all disks configured for your VM Guests. The default setting uses a "direct" lockspace, where the locks are acquired against the actual file paths associated with the VM Guest <disk> devices. For example, flock(2) will be called directly on /var/lib/libvirt/images/my-server/disk0.raw when the VM Guest contains the following <disk> device:

<disk type='file' device='disk'>
 <driver name='qemu' type='raw'/>
 <source file='/var/lib/libvirt/images/my-server/disk0.raw'/>
 <target dev='vda' bus='virtio'/>
</disk>

The virtlockd configuration can be changed by editing the file /etc/libvirt/qemu-lockd.conf. It also contains detailed comments with further information. Make sure to activate configuration changes by reloading virtlockd:

rcvirtlockd reload
[Note]Locking Currently Only Available for All Disks

As of SUSE Linux Enterprise 11 SP3 locking can only be activated globally, so that all virtual disks are locked. Support for locking selected disks is planned for future releases.

8.3.2.1. Enabling an Indirect Lockspace

virtlockd's default configuration uses a direct lockspace, where the locks are acquired against the actual file paths associated with the <disk> devices. If the disk file paths are not accessible to all hosts, virtlockd can be configured to allow an indirect lockspace, where a hash of the disk file path is used to create a file in the indirect lockspace directory. The locks are then held on these hash files instead of the actual disk file paths. Indirect lockspace is also useful if the file system containing the disk files does not support fcntl() locks. An indirect lockspace is specified with the file_lockspace_dir setting:

file_lockspace_dir = "/MY_LOCKSPACE_DIRECTORY"

8.3.2.2. Enable Locking on LVM or iSCSI Volumes

When wanting to lock virtual disks placed on LVM or iSCSI volumes shared by several hosts, locking needs to be done by UUID rather than by path (which is used by default). Furthermore, the lockspace directory needs to be placed on a shared file system accessible by all hosts sharing the volume. Set the following options for LVM and/or iSCSI:

lvm_lockspace_dir = "/MY_LOCKSPACE_DIRECTORY"
iscsi_lockspace_dir = "/MY_LOCKSPACE_DIRECTORY"

Chapter 9. Configuring Virtual Machines

Abstract

Virtual Machine Manager's Details view offers in-depth information about the VM Guest's complete configuration and hardware equipment. Using this view, you can also change the guest configuration or add and modify virtual hardware. To access this view, open the guests console in Virtual Machine Manager and either choose View+Details from the menu, or click on the blue information icon in the toolbar.

Figure 9.1. Details View of a VM Guest

Details View of a VM Guest

9.1. Enabling Seamless and Synchronized Cursor Movement

When you click within a VM Guest's console with the mouse, the cursor is captured by the console window and cannot be used outside the console unless it is explicitly released (by pressing Alt+Ctrl ). To prevent the console from grabbing the key and to enable seamless cursor movement between host and guest instead, add a tablet to the VM Guest.

Adding a tablet has the additional advantage of synchronizing the cursor movement between VM Host Server and VM Guest when using a graphical environment on the guest. With no tablet configured on the guest, you will often see two cursor symbols with one dragging behind the other.

  1. Double-click a VM Guest entry in the Virtual Machine Manager to open its console and switch to the Details view with View+Details.

  2. Click Add Hardware and choose Input and then EvTouch USB Graphics Tablet in the pop-up window. Proceed with Finish.

  3. In case you tried to add the tablet while the guest was still running, you will be asked whether to enable the tablet after the next reboot. Confirm with Yes.

  4. Once you (re)start the VM Guest the tablet is available in the VM Guest.

9.2. Adding a CD/DVD-ROM Device with Virtual Machine Manager

KVM supports CD or DVD-ROMs in VM Guest either by directly accessing a physical drive on the VM Host Server or by accessing ISO images. To create an ISO image from an existing CD or DVD, use dd:

dd if=/dev/cd_dvd_device of=my_distro.iso bs=2048

To add a CD/DVD-ROM device to your VM Guest proceed as follows:

  1. Double-click a VM Guest entry in the Virtual Machine Manager to open its console and switch to the Details view with View+Details.

  2. Click Add Hardware and choose Storage in the pop-up window. Proceed with Forward.

  3. Change the Device Type to IDE CDROM.

  4. Select Select Managed or Other Existing Storage.

    1. To assign the device to a physical medium, enter the path to the VM Host Server's CD/DVD-ROM device (for example, /dev/cdrom) next to the Browse button. Alternatively you may use the Browse button to open a file browser and then click Browse Local to select the device. Assigning the device to a physical medium is only possible, when the Virtual Machine Manager was started on the VM Host Server.

    2. To assign the device to an existing image, click Browse to choose an image from a storage pool. If the Virtual Machine Manager was started on the VM Host Server, you may alternatively choose an image from another location on the file system by clicking Browse Local. Select an image and close the file browser with Choose Volume.

  5. Proceed with Forward to review the settings. Apply them with Finish, Yes, and Apply.

  6. Reboot the VM Guest to make the new device available. For further information also see Section 9.4, “Ejecting and Changing Floppy or CD/DVD-ROM Media with Virtual Machine Manager”.

9.3. Adding a Floppy Device with Virtual Machine Manager

Currently KVM only supports the use of floppy disk images—using a physical floppy drive is not supported. Create a floppy disk image from an existing floppy using dd:

dd if=/dev/fd0 of=/var/lib/libvirt/images/floppy.img

To create an empty floppy disk image use one of the following commands:

# raw image
dd if=/dev/zero of=/var/lib/libvirt/images/floppy.img bs=512 count=2880

# FAT formatted image
mkfs.msdos -C /var/lib/libvirt/images/floppy.img 1440

To add a floppy device to your VM Guest proceed as follows:

  1. Double-click a VM Guest entry in the Virtual Machine Manager to open its console and switch to the Details view with View+Details.

  2. Click Add Hardware and choose Storage in the pop-up window. Proceed with Forward.

  3. Change the Device Type to Floppy Disk.

  4. Choose Select Managed or Other Existing Storage and click Browse to choose an existing image from a storage pool. If Virtual Machine Manager was started on the VM Host Server, you may alternatively choose an image from another location on the file system by clicking Browse Local. Select an image and close the file browser with Choose Volume.

  5. Proceed with Forward to review the settings. Apply them with Finish, Yes, and Apply.

  6. Reboot the VM Guest to make the new device available. For further information also see Section 9.4, “Ejecting and Changing Floppy or CD/DVD-ROM Media with Virtual Machine Manager”.

9.4. Ejecting and Changing Floppy or CD/DVD-ROM Media with Virtual Machine Manager

Regardless whether you are using the VM Host Server's physical CD/DVD-ROM device or an ISO/Floppy image: before you can change the media or image of an existing device in the VM Guest, you first need to disconnect the media from the guest.

  1. Double-click a VM Guest entry in the Virtual Machine Manager to open its console and switch to the Details view with View+Details.

  2. Choose the Floppy or CD/DVD-ROM device and eject the media by clicking Disconnect.

  3. To insert a new media, click Connect.

    1. If using the VM Host Server's physical CD/DVD-ROM device, first change the media in the device (this may require to unmount it on the VM Host Server before it can be ejected). Then choose CD-ROM or DVD and select the device from the drop-down list.

    2. If using an ISO image, choose ISO image Location and select an image by clicking Browse. When connecting from a remote host, you may only choose images from existing storage pools.

  4. Click OK to finish. The new media can now be accessed in the VM Guest.

9.5. Adding a PCI Device with Virtual Machine Manager

You can add PCI devices to guests using the graphical virt-manager tool. Once the PCI device is assigned to one VM Guest, it cannot be used by another one unless re-assigned. The following procedure adds a USB controller to a virtualized guest.

  1. Double-click a VM Guest entry in the Virtual Machine Manager to open its console and switch to the Details view with View+Details.

  2. Click Add Hardware and choose the PCI Host Device category in the left pane. A list of host PCI devices appears in the right part of the window.

  3. From the list of available PCI devices, choose the USB controller to assign to the VM Guest. It may read for example USB2 Enhanced Host Controller. Confirm with Finish.

    [Tip]

    You cannot assign a PCI device live to a running VM Guest. If you are trying to add a PCI device to a running machine, the Virtual Machine Manager will ask if you want to assign the PCI device after the next VM Guest shutdown. Confirm with Yes, and after you reboot the VM Guest, the device assignment will be finished.

9.6. Adding a PCI Device with virsh

To dedicate and assign a PCI device to VM Guest with virsh, follow these steps:

  1. Identify the PCI device.

    Use the virsh nodedev-list or lspci -n commands to identify the PCI device designated for pass-through to VM Guest.

    The following command lists available PCI devices only:

    virsh nodedev-list | grep pci

    Note that PCI devices are identified by a string in the following format (8086 is a variable that represents Intel architecture, and **** stands for a four digit hexadecimal code specific to each device):

    pci_8086_****

    Remember the PCI device number, you will need it in future steps.

  2. Gather the information about the domain, bus, and function:

    # virsh nodedev-dumpxml pci_8086_1d26
    <device>
      <name>pci_8086_1d26</name>
      <parent>computer</parent>
      <driver>
        <name>ehci_hcd</name>
      </driver>
      <capability type='pci'>
        <domain>0</domain>
        <bus>0</bus>
        <slot>29</slot>
        <function>0</function>
        <product id='0x1d26'>Patsburg USB2 Enhanced Host Controller #1</product>
        <vendor id='0x8086'>Intel Corporation</vendor>
        <capability type='virt_functions'>
        </capability>
      </capability>
    </device>
  3. Detach the device from the host system prior to attaching it to VM Guest.

    # virsh nodedev-detach pci_8086_1d26 
      Device pci_8086_1d26 detached
  4. Convert the bus, slot, and function value from decimal to hexadecimal, and prepend '0x' to tell the system that the value is hexadecimal. In our example, bus = 0, slot = 29, and function = 0. Their hexadecimal values are:

    # printf %x 0
    0
    # printf %x 29
    1d

    Bus and function hexadecimal numbers are '0x00', while slot number is '0x1d'.

  5. Run virsh edit on your domain, and add the following device entry in the <devices> section.

    <hostdev mode='subsystem' type='pci' managed='no'>
      <source>
        <address domain='0x0000' bus='0x00' slot='0x1d' function='0x00'/>
      </source>
    </hostdev>
    [Tip]'managed' vs. 'unmanaged'

    libvirt recognizes two modes to handle PCI devices: they can be either 'managed' or 'unmanaged'. In the managed case, libvirt will handle all the details of unbinding the device from the existing driver if needed, resetting the device, binding it to pci-stub before starting the domain, etc. When the domain is terminated or the device is removed from the domain, libvirt will unbind from pci-stub and rebind to the original driver in the case of a managed device. If the device is unmanaged, the user must take care to ensure all of these management aspects of the device are done before assigning it to a domain, and after the device is no longer used by the domain.

    In our example, the managed='no' option means that the device is 'unmanaged', and we need to take care of the related driver with the virsh nodedev-detach and virsh nodedev-attach commands. To switch the device mode to 'managed', replace the snippet with managed='yes', and skip the remaining steps (apart from starting the guest).

  6. Once the VM Guest system is ready to use the PCI device, tell the host to stop using it. First check what driver the host system is using for the PCI device.

    # readlink /sys/bus/pci/devices/0000\:00\:1d.0/driver
    ../../../bus/pci/drivers/pci-stub
  7. In our case, the pci-stub driver is loaded, so you can start the virtual machine. It will be able to use the PCI device automatically.

    # virsh start sles11
    [Tip]

    When using a multi-function PCI device that does not support FLR (function level reset) or PM (power management) reset, you need to detach all its functions from the VM Host Server. The device must be reset for security reasons, and without FLR or PM reset, you must reset the whole device. libvirt will refuse to do this if a function of the device is still in use by the VM Host Server or another VM Guest.

    You can safely detach a device function from the VM Guest with the virsh nodedev-detach command.

    [Tip]

    If your PCI device is not 'managed', and the driver controlling the PCI device is not pci-stub, you have to detach it from the device first:

    virsh nodedev-detach pci_8086_1d26
    [Tip]

    If you are running SE-Linux on your host, you need to disable it for now with

    # setsebool -P virt_use_sysfs 1

    and then start the virtual machine.

9.7. Clock Settings

Keeping the correct time in a VM Guest is one of the more difficult aspects of virtualization. Keeping the correct time is especially important for network applications and is also a prerequisite to do a live migration of a VM Guest.

[Tip]Time Keeping on the VM Host Server

It is strongly recommended to ensure the VM Host Server keeps the correct time as well, for example, by utilizing NTP (see Chapter 23, Time Synchronization with NTP (↑Administration Guide) for more information).

9.7.1. Using kvm_clock

KVM provides a paravirtualized clock which is currently supported by SUSE Linux Enterprise Server 10 SP3 and newer and RedHat Enterprise Linux 5.4 and newer via the kvm_clock driver. It is strongly recommended to use kvm_clock when available.

Use the following command inside a VM Guest running Linux to check whether the driver kvm_clock has been loaded:

~ # dmesg | grep kvm-clock
[    0.000000] kvm-clock: cpu 0, msr 0:7d3a81, boot clock
[    0.000000] kvm-clock: cpu 0, msr 0:1206a81, primary cpu clock
[    0.012000] kvm-clock: cpu 1, msr 0:1306a81, secondary cpu clock
[    0.160082] Switching to clocksource kvm-clock

To check which clock source is currently used, run the following command in the VM Guest. It should output kvm-clock:

cat /sys/devices/system/clocksource/clocksource0/current_clocksource
[Important]kvm-clock and NTP

When using kvm-clock, it is not recommended to use NTP in the VM Guest, as well. Using NTP on the VM Host Server, however, is still recommended.

9.7.2. Other Time Keeping Methods

The paravirtualized kvm-clock is currently not available for SUSE Linux Enterprise Server 9 and Windows operating systems. For Windows, use the Windows Time Service Tools for time synchronization (see http://technet.microsoft.com/en-us/library/cc773263%28WS.10%29.aspx for more information).

Correct time keeping in SUSE Linux Enterprise Server 9 SP4 can be achieved by using special boot parameters:

32-bit Kernel:clock=pmtmr
64-bit Kernel:ignore_lost_ticks

Chapter 10. Administrating VM Guests

10.1. Migrating VM Guests

One of the major advantages of virtualization is the fact that VM Guests are portable. When a VM Host Server needs to go down for maintenance, or when the host gets overloaded, the guests can easily be moved to another VM Host Server. KVM and Xen even support live migrations during which the VM Guest is constantly available.

In order to successfully migrate a VM Guest to another VM Host Server, the following requirements need to be met:

  • Host and target must have same processor manufacturer (Intel or AMD).

  • Storage devices must be accessible from both machines (for example, via NFS or iSCSI) and must be configured as a storage pool on both machines (see Chapter 8, Managing Storage for more information). This is also true for CD-ROM or floppy images that are connected during the move (however, you may disconnect them prior to the move as described in Section 9.4, “Ejecting and Changing Floppy or CD/DVD-ROM Media with Virtual Machine Manager”).

  • libvirtd needs to run on both VM Host Servers and you must be able to open a remote libvirt connection between the target and the source host (or vice versa). Refer to Section 7.2, “Configuring Remote Connections” for details.

  • If a firewall is running on the target host ports need to be opened to allow the migration. If you do not specify a port during the migration process, libvirt chooses one from the range 49152:49215. Make sure that either this range (recommended) or a dedicated port of your choice is opened in the firewall on the target host.

  • Host and target machine should be in the same subnet on the network, otherwise networking will not work after the migration.

  • No running or paused VM Guest with the same name must exist on the target host. If a shut down machine with the same name exists, its configuration will be overwritten.

  • Only the default CPU model (qemu64) should be used when migrating VM Guests.

  • SATA disk device type is not migratable.

  • File system pass-through feature is incompatible with migration.

10.1.1. Migrating with virt-manager

When using the Virtual Machine Manager to migrate VM Guests, it does not matter on which machine it is started. You can start Virtual Machine Manager on the source or the target host or even on a third host. In the latter case you need to be able to open remote connections to both the target and the source host.

  1. Start Virtual Machine Manager and establish a connection to the target or the source host. If the Virtual Machine Manager was started neither on the target nor the source host, connections to both hosts need to be opened.

  2. Right-click on the VM Guest that is to be migrated and choose Migrate. Make sure the guest is running or paused - it is not possible to migrate guests that are shut off.

  3. Choose a New Host for the VM Guest. If the desired target host does not show up, make sure a connection to this host has been established.

    By default, a live migration is performed. If you prefer an offline migration where the VM Guest is paused during the migration, tick Migrate offline.

  4. Click Migrate to start a migration with the default port and bandwidth.

    In order to change these defaults, make the advanced options available by clicking the triangle at Advanced Options. Here you can enter the target host's Address (IP address or hostname), a port and the bandwidth in megabit per second (Mbps). If you specify a Port, you must also specify an Address; the Bandwidth is optional.

  5. Once the migration is complete, the Migrate window closes and the VM Guest is now listed on the new host in the Virtual Machine Manager Window. The original VM Guest will still be available on the target host (in state shut off).

10.1.2. Migrating with virsh

To migrate a VM Guest with virsh migrate, you need to have direct or remote shell access to the VM Host Server, because the command needs to be run on the host. Basically the migration command looks like this

virsh migrate [OPTIONS] VM_ID_or_NAMECONNECTION URI [--migrateuri tcp://REMOTE_HOST:PORT]

The most important options are listed below. See virsh help migrate for a full list.

--live

Does a live migration. If not specified, an offline migration where the VM Guest is paused during the migration, will be performed.

--suspend

Does an offline migration and does not restart the VM Guest on the target host.

--persistent

By default a migrated VM Guest will be migrated transient, so its configuration is automatically deleted on the target host if it is shut down. Use this switch to make the migration persistent.

--undefinesource

When specified, the VM Guest definition on the source host will be deleted after a successful migration (however, virtual disks attached to this guest will not be deleted).

The following examples use mercury.example.com as the source system and jupiter.example.com as the target system, the VM Guest's name is opensuse11 with Id 37.

Offline migration with default parameters
virsh migrate 37 qemu+ssh://tux@jupiter.example.com/system
Transient live migration with default parameters
virsh migrate --live opensuse11 qemu+ssh://tux@jupiter.example.com/system
Persistent live migration; delete VM definition on source
virsh migrate --live --persistent --undefinesource 37 \
qemu+tls://tux@jupiter.example.com/system
Offline migration using port 49152
virsh migrate opensuse11 qemu+ssh://tux@jupiter.example.com/system \
--migrateuri tcp://@jupiter.example.com:49152
[Note]Transient vs. Persistent Migrations

By default virsh migrate creates a temporary (transient) copy of the VM Guest on the target host. A shut down version of the original guest description remains on the source host. A transient copy will be deleted from the server once it is shut down.

In order to create a permanent copy of a guest on the target host, use the switch --persistent. A shut down version of the original guest description remains on the source host, too. Use the option --undefinesource together with --persistent for a real move where a permanent copy is created on the target host and the version on the source host is deleted.

It is not recommended to use --undefinesource without the --persistent option, since this will result in the loss of both VM Guest definitions when the guest is shut down on the target host.

10.2. Monitoring

10.2.1. Monitoring with Virtual Machine Manager

After starting Virtual Machine Manager and connecting to the VM Host Server, a CPU usage graph of all the running guests is displayed.

It is also possible to get information about disk and network usage with this tool, however, you must first activate this in the Preferences:

  1. Run virt-manager.

  2. Select Edit+Preferences.

  3. Change the tab from General to Stats.

  4. Activate the check boxes for Disk I/O and Network I/O.

  5. If desired, also change the update interval or the number of samples that are kept in the history.

  6. Close the Preferences dialog.

  7. Activate the graphs that should be displayed under View+Graph.

Afterwards, the disk and network statistics are also displayed in the main window of the Virtual Machine Manager.

More precise data is available from the VNC window. Open a VNC window as described in Section 6.2, “Opening a Graphical Console”. Choose Details from the toolbar or the View menu. The statistics are displayed from the Performance entry of the left-hand tree menu.

10.2.2. Monitoring with kvm_stat

kvm_stat can be used to trace KVM performance events. It monitors /sys/kernel/debug/kvm, so it needs the debugfs to be mounted. On SUSE Linux Enterprise Server it should be mounted by default. In case it is not mounted, use the following command:

mount -t debugfs none /sys/kernel/debug

kvm_stat can be used in three different modes:

kvm_stat                    # update in 1 second intervals
kvm_stat -1                 # 1 second snapshot
kvm_stat -l > kvmstats.log  # update in 1 second intervals in log format
                            # can be imported to a spreadsheet

Example 10.1. Typical Output of kvm_stat

kvm statistics

 efer_reload                  0       0
 exits                 11378946  218130
 fpu_reload               62144     152
 halt_exits              414866     100
 halt_wakeup             260358      50
 host_state_reload       539650     249
 hypercalls                   0       0
 insn_emulation         6227331  173067
 insn_emulation_fail          0       0
 invlpg                  227281      47
 io_exits                113148      18
 irq_exits               168474     127
 irq_injections          482804     123
 irq_window               51270      18
 largepages                   0       0
 mmio_exits                6925       0
 mmu_cache_miss           71820      19
 mmu_flooded              35420       9
 mmu_pde_zapped           64763      20
 mmu_pte_updated              0       0
 mmu_pte_write           213782      29
 mmu_recycled                 0       0
 mmu_shadow_zapped       128690      17
 mmu_unsync                  46      -1
 nmi_injections               0       0
 nmi_window                   0       0
 pf_fixed               1553821     857
 pf_guest               1018832     562
 remote_tlb_flush        174007      37
 request_irq                  0       0
 signal_exits                 0       0
 tlb_flush               394182     148

See http://clalance.blogspot.com/2009/01/kvm-performance-tools.html for further information on how to interpret these values.

Part III. Managing Virtual Machines with QEMU

Chapter 11. QEMU Overview

QEMU is a fast, cross-platform Open Source machine emulator which can emulate a huge number of hardware architectures for you. QEMU lets you run a complete unmodified operating system (VM Guest) on top of your existing system (VM Host Server).

You can also use QEMU for debugging purposes - you can easily stop your running virtual machine, inspect its state and save and restore it later.

QEMU consists of the following parts:

  • processor emulator (x86, s390x, PowerPC, Sparc ...)

  • emulated devices (graphic card, network card, hard drives, mice ...)

  • generic devices used to connect the emulated devices to the related host devices

  • descriptions of the emulated machines (PC, Power Mac ...)

  • debugger

  • user interface used to interact with the emulator

As a virtualization solution, QEMU can be run together with the KVM kernel module. If the VM Guest hardware architecture is the same as VM Host Server's architecture, QEMU can take advantage of the KVM acceleration.

Chapter 12. Guest Installation

A virtual machine is comprised of data and operating system files that define the virtual environment. Virtual machines are hosted and controlled by the VM Host Server. This chapter provides generalized instructions for installing virtual machines.

Before creating a virtual machine, consider the following:

  • If you want to use an automated installation file (AutoYaST, NetWare® Response File, or RedHat Kickstart), you need to download it to a directory on the host machine server, or make it available through a network file system.

  • When creating sparse image files, make sure the partition on which you create them always has sufficient free space. The guest system has no means to check the host's disk space. Having no space left on the host partition causes write errors and loss of data on the guest system.

  • NetWare and OES Linux virtual machines need a static IP address for each virtual machine you create.

  • If you are installing Open Enterprise Server (OES) 2 Linux, you need a network installation source for OES 2 Linux software. For procedures to create the installation sources, see the Deployment Guide (↑Deployment Guide).

For further prerequisites, consult the manuals of the respective operating system to install.

12.1. Basic Installation with qemu-kvm

The libvirt-based tools such as virt-manager or vm-install offer convenient interfaces to set up and manage virtual machines. They act as a kind of wrapper for qemu-kvm. However, it is also possible to use qemu-kvm directly without using libvirt-based tools at all.

[Warning]

Virtual machines created with qemu-kvm are not "visible" for the libvirt-based tools.

In the following example, a virtual machine with the same parameters as in Example 5.1, “Interactive Setup on the Command Line Using vm-install will be set up using qemu-kvm. For detailed information on the commands, refer to the respective man pages.

If you do not already have an image of a system which you want to run in a virtualized environment, you need to create one from the installation media. In such case, you need to prepare a hard disk image, and obtain an image of the installation media or the media itself.

Create a hard disk with qemu-img.

qemu-img create1 -f raw2 /images/sles11/hda3 8G4

1

The subcommand create tells qemu-img to create a new image.

2

Specify the disk's format with the -f parameter.

3

The full path to the image file.

4

The size of the image—8 GB in this case. The image is created as a sparse file that grows when the disk is filled with data. The specified size defines the maximum size to which the image file can grow.

After at least one hard disk image is created, you can set up a virtual machine with qemu-kvm that will boot into the installation system:

qemu-kvm -name "sles11"1 -M pc-0.122 -m 7683 \
-smp 24 -boot d5 \
-drive file=/images/sles11/hda,if=virtio,index=0,media=disk,format=raw6 \
-drive file=/isos/SLES-11-SP1-DVD-x86_64-GM-DVD1.iso,index=1,media=cdrom7 \
-net nic,model=virtio,macaddr=52:54:00:05:11:118 \
-vga cirrus9 -balloon virtio10

1

Name of the virtual machine that will be displayed in the window caption and also used for the VNC server. This name must be unique.

2

Specifies the machine type (Standard PC, ISA-only PC, or Intel-Mac). Use qemu-kvm -M ? to display a list of valid parameters. pc-0.12 is the default Standard PC.

3

Maximum amount of memory for the virtual machine.

4

Defines an SMP system with two processors.

5

Specifies the boot order. Valid values are a, b (floppy 1 and 2), c (first hard disk), d (first CD-ROM), or n to p (Ether-boot from network adapter 1-3). Defaults to c.

6

Defines the first (index=0) hard disk. It will be accessed as a paravirtualized (if=virtio) drive in raw format.

7

The second (index=1) image drive will act as a CD-ROM.

8

Defines a paravirtualized (model=virtio) network adapter with the MAC address 52:54:00:05:11:11. Be sure to specify a unique MAC address, otherwise a network conflict may occur.

9

Specifies the graphic card. If you specify none, the graphic card will be disabled.

10

Defines the paravirtualized balloon device that allows to dynamically change the amount of memory (up to the maximum value specified with the parameter -m).

After the installation of the guest operating system finishes, you can easily start the related virtual machine without the need to specify the CD-ROM device:

qemu-kvm -name "sles11" -M pc-0.12 -m 768 \
-smp 2 -boot c \
-drive file=/images/sles11/hda,if=virtio,index=0,media=disk,format=raw \
-net nic,model=virtio,macaddr=52:54:00:05:11:11 \
-vga cirrus -balloon virtio

12.2. Managing Disk Images with qemu-img

In the previous section (see Section 12.1, “Basic Installation with qemu-kvm, we used the qemu-img command to create an image of a hard disk. You can, however, use qemu-img for general disk image manipulation. This section introduces useful qemu-img subcommands to help manage the disk images flexibly.

12.2.1. General Information on qemu-img Invocation

qemu-img uses subcommands (like zypper does) to do specific tasks. Each subcommand understands a different set of options. Some of these options are general and used by more of these subcommands, while some of them are unique to the related subcommand. See the qemu-img manual page (man 1 qemu-img) for a complete list of all supported options. qemu-img uses the following general syntax:

qemu-img subcommand [options]

and supports the following subcommands:

create

Creates a new disk image on the file system.

check

Checks an existing disk image for errors.

convert

Converts an existing disk image to a new one in a different format.

info

Displays information about the relevant disk image.

snapshot

Manages snapshots of existing disk images.

commit

Applies changes made to an existing disk image.

rebase

Creates a new base image based on an existing image.

resize

Increases or decreases the size of an existing image.

12.2.2. Creating, Converting and Checking Disk Images

This section describes how to create disk images, check their condition, convert a disk image from one format to another, and get detailed information about a particular disk image.

12.2.2.1. qemu-img create

Use qemu-img create to create a new disk image for your VM Guest operating system. The command uses the following syntax:

qemu-img create -f fmt1 -o options2 fname3 size4

1

The format of the target image. To get a complete list of image formats supported by QEMU, run qemu-img -h and look at the last line of the output.

2

Some of the image formats support additional options to be passed on the command line. You can specify them here with the -o option. The raw image format supports only the size option, so it is possible to insert -o size=8G instead of adding the size option at the end of the command.

3

Path to the target disk image to be created.

4

Size of the target disk image (if not already specified with the -o size=<image_size> option. Optional suffixes for the image size are K (kilobyte), M (megabyte), G (gigabyte), or T (terabyte).

To create a new disk image sles11sp1.raw in the directory /images growing up to a maximum size of 4 GB, run the following command:

tux@venus:~> qemu-img create -f raw -o size=4G /images/sles11sp1.raw
Formatting '/images/sles11sp1.raw', fmt=raw size=4294967296

tux@venus:~> ls -l /images/sles11sp1.raw
-rw-r--r-- 1 tux users 4294967296 Nov 15 15:56 /images/sles11sp1.raw

tux@venus:~> qemu-img info /images/sles11sp1.raw
image: /images/sles11sp1.raw
file format: raw
virtual size: 4.0G (4294967296 bytes)
disk size: 0

As you can see, the virtual size of the newly created image is 4 GB, but the actual reported disk size is 0 as no data has been written to the image yet.

12.2.2.2. qemu-img convert

Use qemu-img convert to convert disk images to another format. To get a complete list of image formats supported by QEMU, run qemu-img -h and look at the last line of the output. The command uses the following syntax:

qemu-img convert -c1 -f fmt2 -O out_fmt3 -o options4 fname5 out_fname6

1

Applies compression on the target disk image. Only qcow and qcow2 formats support compression.

2

The format of the source disk image. It is autodetected in most cases and can therefore be omitted.

3

The format of the target disk image.

4

Specify additional options relevant for the target image format. Use -o ? to view the list of options supported by the target image format:

5

Path to the source disk image to be converted.

6

Path to the converted target disk image.

tux@venus:~> qemu-img convert -O vmdk /images/sles11sp1.raw \
/images/sles11sp1.vmdk

tux@venus:~> ls -l /images/
-rw-r--r-- 1 tux users 4294967296 16. lis 10.50 sles11sp1.raw
-rw-r--r-- 1 tux users 2574450688 16. lis 14.18 sles11sp1.vmdk

To see a list of options relevant for the selected target image format, run the following command (replace vmdk with your image format):

tux@venus:~> qemu-img convert -O vmdk /images/sles11sp1.raw \
/images/sles11sp1.vmdk -o ?
Supported options:
size             Virtual disk size
backing_file     File name of a base image
compat6          VMDK version 6 image
subformat        VMDK flat extent format, can be one of {monolithicSparse \
    (default) | monolithicFlat | twoGbMaxExtentSparse | twoGbMaxExtentFlat}
scsi             SCSI image

12.2.2.3. qemu-img check

Use qemu-img check to check the existing disk image for errors. Not all disk image formats support this feature. The command uses the following syntax:

qemu-img check -f fmt1 fname2

1

The format of the source disk image. It is autodetected in most cases and can therefore be omitted.

2

Path to the source disk image to be checked.

If no error is found, the command returns no output. Otherwise, the type and number of errors found is shown.

tux@venus:~> qemu-img check -f qcow2 /images/sles11sp1.qcow2
ERROR: invalid cluster offset=0x2af0000
[...]
ERROR: invalid cluster offset=0x34ab0000
378 errors were found on the image.

12.2.2.4. Increasing the Size of an Existing Disk Image

When creating a new image, you must specify its maximum size before the image is created (see Section 12.2.2.1, “qemu-img create”). After you install and run VM Guest for some time, the initial size of the image may no longer be sufficient and you need to add more space to it.

To increase the size of an existing disk image by 2 Gigabytes, use

qemu-img resize /images/sles11sp1.raw +2GB
[Note]

You can resize the raw disk images only. To resize other image formats, convert it to raw with qemu-img convert first.

The image now contains an empty space of 2 GB after the final partition. You can resize the existing partitions or add new ones.

Figure 12.1. New 2GB Partition in Guest YaST Partitioner

New 2GB Partition in Guest YaST Partitioner

12.2.3. Managing Snapshots of Virtual Machines with qemu-img

Virtual machine snapshots are snapshots of the complete environment in which a VM Guest is running. The snapshot includes the state of the processor (CPU), memory (RAM), devices, and all writable disks.

Snapshots are helpful when you need to save your virtual machine in a particular state. For example, after you configured network services on a virtualized server and want to quickly start the virtual machine in the same state you last saved it. Or you can create a snapshot after the virtual machine has been powered off to create a backup state before you try something experimental and possibly make VM Guest unstable. This section introduces the latter case, while the former is described in Chapter 15, Administrating Virtual Machines with QEMU Monitor.

To use snapshots, your VM Guest must contain at least one writable hard disk image in qcow2 format. This device is usually the first virtual hard disk.

Virtual machine snapshots are created with the savevm command in the interactive QEMU monitor. You can assign a 'tag' to each snapshot which makes its identification easier. For more information on QEMU monitor, see Chapter 15, Administrating Virtual Machines with QEMU Monitor.

Once your qcow2 disk image contains saved snapshots, you can inspect them with the qemu-img snapshot command.

[Warning]

Do not create or delete virtual machine snapshots with the qemu-img snapshot command while the virtual machine is running. Otherwise, you can damage the disk image with the state of the virtual machine saved.

12.2.3.1. Listing Existing Snapshots

Use qemu-img snapshot -l disk_image to view a list of all existing snapshots saved in the disk_image image. You can get the list even while the VM Guest is running.

tux@venus:~> qemu-img snapshot -l /images/sles11sp1.qcow2 
Snapshot list:
ID1       TAG2               VM SIZE3        DATE4          VM CLOCK5
1         booting                4.4M 2010-11-22 10:51:10   00:00:20.476
2         booted                 184M 2010-11-22 10:53:03   00:02:05.394
3         logged_in              273M 2010-11-22 11:00:25   00:04:34.843
4         ff_and_term_running    372M 2010-11-22 11:12:27   00:08:44.965

1

Unique identification number of the snapshot. Usually auto-incremented.

2

Unique description string of the snapshot. It is meant as a human readable version of the ID.

3

The disk space occupied by the snapshot. Note that the more memory is consumed by running applications, the bigger the snapshot is.

4

Time and date the snapshot was created.

5

The current state of the virtual machine's clock.

12.2.3.2. Creating Snapshots of a Powered-Off Virtual Machine

Use qemu-img snapshot -c snapshot_title disk_image to create a snapshot of the current state of a virtual machine which was previously powered off.

tux@venus:~> qemu-img snapshot -c backup_snapshot /images/sles11sp1.qcow2
tux@venus:~> qemu-img snapshot -l /images/sles11sp1.qcow2 
Snapshot list:
ID        TAG                 VM SIZE                DATE       VM CLOCK
1         booting                4.4M 2010-11-22 10:51:10   00:00:20.476
2         booted                 184M 2010-11-22 10:53:03   00:02:05.394
3         logged_in              273M 2010-11-22 11:00:25   00:04:34.843
4         ff_and_term_running    372M 2010-11-22 11:12:27   00:08:44.965
5         backup_snapshot           0 2010-11-22 14:14:00   00:00:00.000

Once something breaks in your VM Guest and you need to restore the state of the saved snapshot (id 5 in our example), power off your VM Guest and do the following:

tux@venus:~> qemu-img snapshot -a 5 /images/sles11sp1.qcow2

Next time you run the virtual machine with qemu-kvm, it will be in the state of snapshot number 5.

[Note]

The qemu-img snapshot -c command is not related to the savevm command of QEMU monitor (see Chapter 15, Administrating Virtual Machines with QEMU Monitor. For example, you cannot apply a snapshot with qemu-img snapshot -a on a snapshot created with savevm in QEMU's monitor.

12.2.3.3. Deleting Snapshots

Use qemu-img snapshot -d snapshot_id disk_image to delete old or unneeded snapshots of a virtual machine. This saves some disk space inside the qcow2 disk image as the space occupied by the snapshot data is restored:

tux@venus:~> qemu-img snapshot -d 2 /images/sles11sp1.qcow2

12.2.4. Manipulate Disk Images Effectively

Imagine the following real-life situation: you are a server administrator who runs and manages a number of virtualized operating systems. One group of these systems are based on one specific distribution, while another group (or groups) is based on different versions of the distribution or even on a different (and maybe non-Unix) platform. And to make the case even more complex, individual virtual guest systems based on the same distribution usually differ according to the department and deployment: a file server typically uses different setup and services than a Web server does, while both may still be based on SUSE® Linux Enterprise Server 11 SP1.

With QEMU it is possible to create base disk images. You can use them as template virtual machines. These base images will save you plenty of time because you will never need to install the same operating system more than once.

12.2.4.1. Base and Derived Images

First, build a disk image as usual and install the target system on it. For more information, see Section 12.1, “Basic Installation with qemu-kvm and Section 12.2.2, “Creating, Converting and Checking Disk Images”. Then build a new image while using the first one as a base image. The base image is also called a 'backing' file. After your new 'derived' image is built, never boot the base image again, but boot the derived image instead. Several derived images may depend on one base image at the same time. Therefore, changing the base image can damage the dependencies. While using your derived image, QEMU writes changes to it and uses the base image only for reading.

It is a good practice to create a base image from a freshly installed (and, if needed, registered) operating system with no patches applied and no additional applications installed or removed. Later on, you can create another base image with the latest patches applied and based on the original base image.

12.2.4.2. Creating Derived Images

[Note]

While you can use the raw format for base images, you cannot use it for derived images because the raw format does not support the backing_file option. Use for example the qcow2 format for the derived images.

For example, /images/sles11sp1_base.raw is the base image holding a freshly installed system.

tux@venus:~> qemu-img info /images/sles11sp1_base.raw 
image: /images/sles11sp1_base.raw
file format: raw
virtual size: 4.0G (4294967296 bytes)
disk size: 2.4G

The image's reserved size is 4 GB, the actual size is 2.4 GB, and its format is raw. Create an image derived from the /images/sles11sp1_base.raw base image with:

tux@venus:~> qemu-img create -f qcow2 /images/sles11sp1_derived.qcow2 \
-o backing_file=/images/sles11sp1_base.raw 
Formatting '/images/sles11sp1_derived.qcow2', fmt=qcow2 size=4294967296 \
backing_file='/images/sles11sp1_base.raw' encryption=off cluster_size=0

Look at the derived image details:

tux@venus:~> qemu-img info /images/sles11sp1_derived.qcow2 
image: /images/sles11sp1_derived.qcow2
file format: qcow2
virtual size: 4.0G (4294967296 bytes)
disk size: 140K
cluster_size: 65536
backing file: /images/sles11sp1_base.raw \
(actual path: /images/sles11sp1_base.raw)

Although the reserved size of the derived image is the same as the size of the base image (4 GB), the actual size is 140 KB only. The reason is that only changes made to the system inside the derived image are saved. Run the derived virtual machine, register it, if needed, and apply the latest patches. Do any other changes in the system such as removing unneeded or installing new software packages. Then shut the VM Guest down and examine its details once more:

tux@venus:~> qemu-img info /images/sles11sp1_derived.qcow2
image: /images/sles11sp1_derived.qcow2
file format: qcow2
virtual size: 4.0G (4294967296 bytes)
disk size: 1.1G
cluster_size: 65536
backing file: /images/sles11sp1_base.raw \
(actual path: /images/sles11sp1_base.raw)

The disk size value has grown to 1.1 GB, which is the disk space occupied by the changes on the file system compared to the base image.

12.2.4.3. Rebasing Derived Images

Once you modify the derived image (apply patches, install specific applications, or change the environment settings etc.) into a satisfactory shape, at some point you probably want to create a new base image 'merged' from the base image and the derived one. Your first base image (/images/sles11sp1_base.raw) holds a freshly installed system and can be a template for new modified base images, while the new one can contain the same system as the first one plus all security and update patches applied, for example. After you created this new base image, you can use it as a template for more specialized derived images as well. The new base image becomes independent of the original one. The process of creating base images from derived ones is called 'rebasing':

tux@venus:~> qemu-img convert /images/sles11sp1_derived.qcow2 \
-O raw /images/sles11sp1_base2.raw

This command created the new base image /images/sles11sp1_base2.raw using the raw format.

tux@venus:~> qemu-img info /images/sles11sp1_base2.raw
image: /images/sles11sp1_base2.raw
file format: raw
virtual size: 4.0G (4294967296 bytes)
disk size: 2.8G

The new image is 0.4 gigabytes bigger than the original base image. It uses no backing file, and you can easily create new derived images based upon it. This lets you create a sophisticated hierarchy of virtual disk images for your organization, saving a lot of time and work.

12.2.4.4. Mounting an Image on a VM Host Server

Sometimes it is useful to mount a virtual disk image under the host system. For example, if VM Host Server does not have a network support, this can be the only way to transfer files in and out of a VM Guest.

Linux systems can mount an internal partition of a raw disk image using a 'loopback' device. The first example procedure is more complex but more illustrative, while the second one is straightforward:

Procedure 12.1. Mounting Disk Image by Calculating Partition Offset

  1. Set a loop device on the disk image whose partition you want to mount.

    tux@venus:~> losetup /dev/loop0 /images/sles11sp1_base.raw
  2. Find the sector size and the starting sector number of the partition you want to mount.

    tux@venus:~> fdisk -lu /dev/loop0
    
    Disk /dev/loop0: 4294 MB, 4294967296 bytes
    255 heads, 63 sectors/track, 522 cylinders, total 8388608 sectors
    Units = sectors of 1 * 512 = 5121 bytes
    Disk identifier: 0x000ceca8
    
           Device Boot      Start         End      Blocks   Id  System
    /dev/loop0p1              63     1542239      771088+  82  Linux swap
    /dev/loop0p2   *     15422402    8385929     3421845   83  Linux

    1

    The disk sector size.

    2

    The starting sector of the partition.

  3. Calculate the partition start offset:

    sector_size * sector_start = 512 * 1542240 = 789626880

  4. Delete the loop and mount the partition inside the disk image with the calculated offset on a prepared directory.

    tux@venus:~> losetup -d /dev/loop0
    tux@venus:~> mount -o loop,offset=789626880 \
    /images/sles11sp1_base.raw /mnt/sles11sp1/
    tux@venus:~> ls -l /mnt/sles11sp1/
    total 112
    drwxr-xr-x   2 root root  4096 Nov 16 10:02 bin
    drwxr-xr-x   3 root root  4096 Nov 16 10:27 boot
    drwxr-xr-x   5 root root  4096 Nov 16 09:11 dev
    [...]
    drwxrwxrwt  14 root root  4096 Nov 24 09:50 tmp
    drwxr-xr-x  12 root root  4096 Nov 16 09:16 usr
    drwxr-xr-x  15 root root  4096 Nov 16 09:22 var
    
  5. Copy one or more files onto the mounted partition and unmount it when finished.

    tux@venus:~> cp /etc/X11/xorg.conf /mnt/sles11sp1/root/tmp
    tux@venus:~> ls -l /mnt/sles11sp1/root/tmp
    tux@venus:~> umount /mnt/sles11sp1/

Procedure 12.2. Mounting Disk Image while Utilizing kpartx

  1. Set a loop device on the disk image whose partition you want to mount.

    tux@venus:~> losetup /dev/loop0 /images/sles11sp1_base.raw
  2. Create a device map from the disk image's partitions.

    tux@venus:~> kpartx -a /dev/loop0
  3. Mount any partition of the disk image on a prepared mount point.

    tux@venus:~> mount /dev/mapper/loop0p1 /mnt/p1

    You can replace loop0p1 with the number of the partition you want to mount, for example loop0p3 to mount the third partition on the disk image.

  4. Copy or move files or directories to and from the mounted partition as you like. Once you finish, unmount the partition and delete the loop.

    tux@venus:~> umount /mnt/p1
    tux@venus:~> losetup -d /dev/loop0
[Warning]

Never mount a partition of an image of a running virtual machine in a read-write mode. This could corrupt the partition and break the whole VM Guest.

Chapter 13. Running Virtual Machines with qemu-kvm

Once you have a virtual disk image ready (for more information on disk images, see Section 12.2, “Managing Disk Images with qemu-img), it is time to start the related virtual machine. Section 12.1, “Basic Installation with qemu-kvm introduced simple commands to install and run a VM Guest. This chapter focuses on a more detailed explanation of qemu-kvm usage, and shows solutions of more specific tasks. For a complete list of qemu-kvm's options, see its manual page (man 1 qemu-kvm).

13.1. Basic qemu-kvm Invocation

The qemu-kvm command uses the following syntax:

qemu-kvm options1 disk_img2

1

qemu-kvm understands a large number of options. Most of them define parameters of the emulated hardware, while others affect more general emulator behavior. If you do not supply any options, default values are used, and you need to supply the path to a disk image to be run.

2

Path to the disk image holding the guest system you want to virtualize. qemu-kvm supports a large number of image formats. Use qemu-img --help to list them. If you do not supply the path to a disk image as a separate argument, you have to use the -drive file= option.

13.2. General qemu-kvm Options

This section introduces general qemu-kvm options and options related to the basic emulated hardware, such as virtual machine's processor, memory, model type, or time processing methods.

-name name_of_guest

Specifies the name of the running guest system. The name is displayed in the window caption and also used for the VNC server.

-boot options

Specifies the order in which the defined drives will be booted. Drives are represented by letters, where 'a' and 'b' stands for the floppy drives 1 and 2, 'c' stands for the first hard disk, 'd' stands for the first CD-ROM drive, and 'n' to 'p' stand for Ether-boot network adapters.

For example, qemu-kvm [...] -boot order=ndc first tries to boot from network, then from the first CD-ROM drive, and finally from the first hard disk.

-pidfile fname

Stores the QEMU's process identification number (PID) in a file. This is useful if you run QEMU from a script.

-nodefaults

By default QEMU creates basic virtual devices even if you do not specify them on the command line. This option turns this feature off, and you must specify every single device manually, including graphical and network cards, parallel or serial ports, or virtual consoles. Even QEMU monitor is not attached by default.

-daemonize

'Daemonizes' the QEMU process after it is started. QEMU will detach from the standard input and standard output after it is ready to receive connections on any of its devices.

13.2.1. Basic Virtual Hardware

-M machine_type

Specifies the type of the emulated machine. Run qemu-kvm -M help to view a list of supported machine types.

tux@venus:~> qemu-kvm -M help
Supported machines are:
q35                  Standard PC (Q35 + ICH9, 2009) (alias of pc-q35-1.4)
pc-q35-1.4           Standard PC (Q35 + ICH9, 2009)
pc                   Standard PC (i440FX + PIIX, 1996) 
pc-i440fx-1.4        Standard PC (i440FX + PIIX, 1996) (default)
pc-1.3               Standard PC
pc-1.2               Standard PC
pc-1.1               Standard PC
pc-1.0               Standard PC
pc-0.15              Standard PC
pc-0.14              Standard PC
pc-0.13              Standard PC
pc-0.12              Standard PC
pc-0.11              Standard PC, qemu 0.11
pc-0.10              Standard PC, qemu 0.10
isapc                ISA-only PC
none                 empty machine
-m megabytes

Specifies how many megabytes are used for the virtual RAM size. Default is 512 MB.

-balloon virtio

Specifies a paravirtualized device to dynamically change the amount of virtual RAM memory assigned to VM Guest. The top limit is the amount of memory specified with -m.

-cpu cpu_model

Specifies the type of the processor (CPU) model. Run qemu-kvm -cpu ? to view a list of supported CPU models.

tux@venus:~> qemu-kvm -cpu help
 x86           qemu64  QEMU Virtual CPU version 1.4.0                  
 x86           phenom  AMD Phenom(tm) 9550 Quad-Core Processor         
 x86         core2duo  Intel(R) Core(TM)2 Duo CPU     T7700  @ 2.40GHz 
 x86            kvm64  Common KVM processor                            
 x86           qemu32  QEMU Virtual CPU version 1.4.0                  
 x86            kvm32  Common 32-bit KVM processor                     
 x86          coreduo  Genuine Intel(R) CPU           T2600  @ 2.16GHz 
 x86              486                                                  
 x86          pentium                                                  
 x86         pentium2                                                  
 x86         pentium3                                                  
 x86           athlon  QEMU Virtual CPU version 1.4.0                  
 x86             n270  Intel(R) Atom(TM) CPU N270   @ 1.60GHz          
 x86           Conroe  Intel Celeron_4x0 (Conroe/Merom Class Core 2)   
 x86           Penryn  Intel Core 2 Duo P9xxx (Penryn Class Core 2)    
 x86          Nehalem  Intel Core i7 9xx (Nehalem Class Core i7)       
 x86         Westmere  Westmere E56xx/L56xx/X56xx (Nehalem-C)          
 x86      SandyBridge  Intel Xeon E312xx (Sandy Bridge)                
 x86          Haswell  Intel Core Processor (Haswell)                  
 x86       Opteron_G1  AMD Opteron 240 (Gen 1 Class Opteron)           
 x86       Opteron_G2  AMD Opteron 22xx (Gen 2 Class Opteron)          
 x86       Opteron_G3  AMD Opteron 23xx (Gen 3 Class Opteron)          
 x86       Opteron_G4  AMD Opteron 62xx class CPU                      
x86       Opteron_G5  AMD Opteron 63xx class CPU
-smp number_of_cpus

Specifies how many CPUs will be emulated. QEMU supports up to 255 CPUs on the PC platform (up to 64 with KVM acceleration used). This option also takes other CPU-related parameters, such as number of sockets, number of cores per socket, or number of threads per core.

Following is an example of a working qemu-kvm command line:

qemu-kvm -name "SLES 11 SP1" -M pc-0.12 -m 512 -cpu kvm64 \
-smp 2 /images/sles11sp1.raw

Figure 13.1. QEMU Window with SLES 11 SP1 as VM Guest

QEMU Window with SLES 11 SP1 as VM Guest

-no-acpi

Disables ACPI support. Try to use it if VM Guest reports problems with ACPI interface.

-S

QEMU starts with CPU stopped. To start CPU, enter c in QEMU monitor. For more information, see Chapter 15, Administrating Virtual Machines with QEMU Monitor.

13.2.2. Storing and Reading Configuration of Virtual Devices

-readconfig cfg_file

Instead of entering the devices configuration options on the command line each time you want to run VM Guest, qemu-kvm can read it from a file which was either previously saved with -writeconfig or edited manually.

-writeconfig cfg_file

Dumps the current virtual machine devices configuration to a text file. It can be consequently re-used with the -readconfig option.

tux@venus:~> qemu-kvm -name "SLES 11 SP1" -M pc-0.12 -m 512 -cpu kvm64 \
-smp 2 /images/sles11sp1.raw -writeconfig /images/sles11sp1.cfg
(exited)
tux@venus:~> more /images/sles11sp1.cfg
# qemu config file

[drive]
  index = "0"
  media = "disk"
  file = "/images/sles11sp1_base.raw"

This way you can effectively manage the configuration of your virtual machines' devices in a well-arranged way.

13.2.3. Guest Real-time Clock

-rtc options

Specifies the way the RTC is handled inside a VM Guest. By default, the clock of the guest is derived from that of the host system. Therefore, it is recommended that the host system clock is synchronized with an accurate external clock (for example, via NTP service).

If you need to isolate the VM Guest clock from the host one, specify clock=vm instead of the default clock=host.

You can also specify a 'starting point' for VM Guest clock with the base option:

qemu-kvm [...] -rtc clock=vm,base=2010-12-03T01:02:00

Instead of a timestamp, you can specify utc or localtime. The former instructs VM Guest to start at the current UTC value (Coordinated Universal Time, see http://en.wikipedia.org/wiki/UTC), while the latter applies the local time setting.

13.3. Using Devices in QEMU

QEMU virtual machines emulate all devices needed to run a VM Guest. QEMU supports, for example, several types of network cards, block devices (hard and removable drives), USB devices, character devices (serial and parallel ports), or multimedia devices (graphic and sound cards). For satisfactory operation and performance of the virtual machine, some or all of these devices must be configured correctly. This section introduces options to configure various types of supported devices.

[Tip]

If your device, such as -drive, needs a special driver and driver properties to be set, specify them with the -device option, and identify with drive= suboption. For example

qemu [...] -drive if=none,id=drive0,format=raw \
-device virtio-blk-pci,drive=drive0,scsi=off ...

To get help on available drivers and their properties, use -device ? and -device driver,?.

13.3.1. Block Devices

Block devices are vital for virtual machines. In general, these are fixed or removable storage media usually referred to as 'drives'. One of the connected hard drives typically holds the guest operating system to be virtualized.

Virtual machine drives are defined with -drive. This option uses many suboptions, some of which are described in this section. For their complete list, see the manual page (man 1 qemu-kvm).

Sub-options for the -drive Option

file=image_fname

Specifies the path to the disk image which will be used with this drive. If not specified, an empty (removable) drive is assumed.

if=drive_interface

Specifies the type of interface to which the drive is connected. Currently only floppy, ide, or virtio are supported by SUSE. virtio defines a paravirtualized disk driver. Default is ide.

index=index_of_connector

Specifies the index number of a connector on the disk interface (see the if option) where the drive is connected. If not specified, the index is automatically incremented.

media=type

Specifies the type of the media. Can be disk for hard disks, or cdrom for removable CD-ROM drives.

format=img_fmt

Specifies the format of the connected disk image. If not specified, the format is autodetected. Currently, SUSE supports qcow2, qed and raw formats.

cache=method

Specifies the caching method for the drive. Possible values are unsafe, writethrough, writeback, directsync, or none. For the qcow2 image format, choose writeback if you care about performance. none disables the host page cache and, therefore, is the safest option. Default for image files is writeback.

[Tip]

To simplify defining of block devices, QEMU understands several shortcuts which you may find handy when entering the qemu-kvm command line.

You can use

qemu-kvm -cdrom /images/cdrom.iso

instead of

qemu-kvm -drive file=/images/cdrom.iso,index=2,media=cdrom

and

qemu-kvm -hda /images/imagei1.raw -hdb /images/image2.raw -hdc \
/images/image3.raw -hdd /images/image4.raw

instead of

qemu-kvm -drive file=/images/image1.raw,index=0,media=disk \
-drive file=/images/image2.raw,index=1,media=disk \
-drive file=/images/image3.raw,index=2,media=disk \
-drive file=/images/image4.raw,index=3,media=disk
[Tip]Using Host Drives Instead of Images

Normally you will use disk images (see Section 12.2, “Managing Disk Images with qemu-img) as disk drives of the virtual machine. However, you can also use existing VM Host Server disks, connect them as drives, and access them from VM Guest. Use the host disk device directly instead of disk image filenames.

To access the host CD-ROM drive, use

qemu-kvm [...] -drive file=/dev/cdrom,media=cdrom

To access the host hard disk, use

qemu-kvm [...] -drive file=/dev/hdb,media=disk

When accessing the host hard drive from VM Guest, always make sure the access is read-only. You can do so by modifying the host device permissions.

13.3.1.1. virtio-blk-data-plane

The virtio-blk-data-plane is a new performance feature for KVM. It enables a high-performance code path for I/O requests coming from VM Guests. More specifically, this feature introduces dedicated threads (one per virtual block device) to process I/O requests going through the virtio-blk driver. It makes use of Linux AIO (asynchronous I/O interface) support in the VM Host Server Kernel directly—without the need to go through the QEMU block layer. Therefore it can sustain very high I/O rates on storage setups.

The virtio-blk-data-plane feature can be enabled or disabled by the x-data-plane=on|off option on the qemu command line when starting the VM Guest:

qemu [...] -drive if=none,id=drive0,cache=none,aio=native,\
format=raw,file=filename -device virtio-blk-pci,drive=drive0,scsi=off,\
config-wce=off,x-data-plane=on [...]

As of now, the virtio-blk-data-plane has the following limitations:

  • Only raw image format is supported.

  • No support for live migration.

  • Block jobs and hot unplug operations fail with -EBUSY.

  • I/O throttling limits are ignored.

  • Only Linux VM Host Servers are supported because of the Linux AIO usage, but non-Linux VM Guests are supported.

[Important]

The virtio-blk-data-plane feature is not yet supported in SUSE Linux Enterprise Server. It is released as a technical preview only.

13.3.2. Graphic Devices and Display Options

This section describes QEMU options affecting the type of the emulated video card and the way VM Guest graphical output is displayed.

13.3.2.1. Defining Video Cards

QEMU uses -vga to define a video card used to display VM Guest graphical output. The -vga option understands the following values:

none

Disables video cards on VM Guest (no video card is emulated). You can still access the running VM Guest via the QEMU monitor and the serial console.

std

Emulates a standard VESA 2.0 VBE video card. Use it if you intend to use high display resolution on VM Guest.

cirrus

Emulates Cirrus Logic GD5446 video card. Good choice if you insist on high compatibility of the emulated video hardware. Most operating systems (even Windows 95) recognize this type of card.

[Tip]

For best video performance with the cirrus type, use 16-bit color depth both on VM Guest and VM Host Server.

13.3.2.2. Display Options

The following options affect the way VM Guest graphical output is displayed.

-nographic

Disables QEMU's graphical output. The emulated serial port is redirected to the console.

After starting the virtual machine with -nographic, press Ctrl+A H in the virtual console to view the list of other useful shortcuts, for example, to toggle between the console and the QEMU monitor.

tux@venus:~> qemu-kvm -hda /images/sles11sp1_base.raw -nographic

C-a h    print this help
C-a x    exit emulator
C-a s    save disk data back to file (if -snapshot)
C-a t    toggle console timestamps
C-a b    send break (magic sysrq)
C-a c    switch between console and monitor
C-a C-a  sends C-a
(pressed C-a c)

QEMU 0.12.5 monitor - type 'help' for more information
(qemu)
-no-frame

Disables decorations for the QEMU window. Convenient for dedicated desktop workspace.

-full-screen

Starts QEMU graphical output in full screen mode.

-no-quit

Disables the 'close' button of QEMU window and prevents it from being closed by force.

-alt-grab, -ctrl-grab

By default QEMU window releases the 'captured' mouse after Ctrl+Alt is pressed. You can change the key combination to either Ctrl+Alt+Shift (-alt-grab), or Right Ctrl (-ctrl-grab).

13.3.3. USB Devices

There are basically two ways to create USB devices usable by the VM Guest in KVM: you can either emulate new USB devices inside a VM Guest, or assign an existing host USB device to a VM Guest. To use USB devices in QEMU you first need to enable the generic USB driver with the -usb option. Then you can specify individual devices with the -usbdevice option.

13.3.3.1. Emulating USB Devices in VM Guest

SUSE currently supports the following types of USB devices: disk, host, serial, braille, netmouse and tablet.

Types of USB devices for the -usbdevice option

disk

Emulates a mass storage device based on file. The optional format option is used rather than detecting the format.

qemu-kvm [...] -usbdevice
        disk:format=raw:/virt/usb_disk.raw
host

Pass through the host device (identified by bus.addr).

serial

Serial converter to a host character device.

braille

Emulates a braille device using BrlAPI to display the braille output.

net

Emulates a network adapter that supports CDC ethernet and RNDIS protocols.

mouse

Emulates a virtual USB mouse. This option overrides the default PS/2 mouse emulation. The following example shows the hardware status of a mouse on VM Guest started with qemu-kvm [...] -usbdevice mouse:

tux@venus:~> hwinfo --mouse
20: USB 00.0: 10503 USB Mouse
[Created at usb.122]
UDI: /org/freedesktop/Hal/devices/usb_device_627_1_1_if0
[...]
Hardware Class: mouse
Model: "Adomax QEMU USB Mouse"
Hotplug: USB
Vendor: usb 0x0627 "Adomax Technology Co., Ltd"
Device: usb 0x0001 "QEMU USB Mouse"
[...]
tablet

Emulates a pointer device that uses absolute coordinates (such as touchscreen). This option overrides the default PS/2 mouse emulation. The tablet device is useful if you are viewing VM Guest via the VNC protocol. See Section 13.5, “Viewing a VM Guest with VNC” for more information.

13.3.3.2. USB Pass-Through

To assign an existing host USB device to a VM Guest, you need to find out its host bus and device ID.

tux@vmhost:~> lsusb
[...]
Bus 002 Device 005: ID 12d1:1406 Huawei Technologies Co., Ltd. E1750
[...]

In the above example, we want to assign a USB stick connected to the host's USB bus number 2 with device number 5. Now run the VM Guest with the following additional options:

qemu-kvm [...] -usb -device usb-host,hostbus=2,hostaddr=5

After the guest is booted, check that the assigned USB device is present on it.

tux@vmguest:~> lsusb
[...]
Bus 001 Device 002: ID 12d1:1406 Huawei Technologies Co., Ltd. E1750
[...]
[Note]

The guest operating system must take care of mounting the assigned USB device so that it is accessible for the user.

13.3.4. PCI Pass-Through

PCI Pass-Through is a technique to give your VM Guest exclusive access to a PCI device.

[Note]

To make use of PCI Pass-Through, your motherboard chipset, BIOS, and CPU must have support for AMD's IOMMU (or VT-d in Intel speak) virtualization technology. To make sure that your computer supports this feature, ask your supplier specifically to deliver a system that supports PCI Pass-Through.

[Note]

Assignment of graphics cards is not supported by SUSE.

Procedure 13.1. Configuring PCI Pass-Through

  1. Make sure that CONFIG_DMAR_DEFAULT_ON is set in the host's running Kernel:

    grep CONFIG_DMAR_DEFAULT_ON /boot/config-`uname -r`

    If this option is not set, edit your boot loader configuration and add intel_iommu=on (Intel machines) or iommu=pt iommu=1 (AMD machines). Then reboot the host machine.

  2. Check that IOMMU is actively enabled and recognized on the host. Run dmesg | grep -e DMAR -e IOMMU on Intel machines, or dmesg | grep AMD-Vi on AMD machines. If you get no output, check carefully if your hardware supports IOMMU (VT-d) and check that it has been enabled in BIOS.

  3. Identify the host PCI device to assign to the guest.

    tux@vmhost:~> lspci -nn
    [...] 00:1b.0 Audio device [0403]: Intel Corporation 82801H (ICH8 Family) \
    HD Audio Controller [8086:284b] (rev 02) [...]

    Note down the device (00:1b.0) and vendor (8086:284b) ID.

  4. Unbind the device from host Kernel driver and bind it to the PCI stub driver.

    tux@vmhost:~> modprobe pci_stub
    tux@vmhost:~> echo "8086 284b" > /sys/bus/pci/drivers/pci-stub/new_id
    tux@vmhost:~> echo "0000:00:1b.0" > /sys/bus/pci/devices/0000:00:1b.0/driver/unbind
    tux@vmhost:~> echo "0000:00:1b.0" > /sys/bus/pci/drivers/pci-stub/bind
  5. Now run the VM Guest with the PCI device assigned.

    qemu-kvm [...] -device pci-assign,host=00:1b.0
[Note]

If the PCI device shares IRQ with other devices, it cannot be assigned to a VM Guest.

KVM also supports PCI device hot-plugging to a VM Guest. To achieve this, you need to switch to a QEMU monitor (see Chapter 15, Administrating Virtual Machines with QEMU Monitor for more information) and issue the following commands:

  • hot add:

    device_add pci-assign,host=00:1b.0,id=new_pci_device
  • hot remove:

    device_del new_pci_device

13.3.5. Character Devices

Use -chardev to create a new character device. The option uses the following general syntax:

qemu-kvm [...] -chardev backend_type,id=id_string

where backend_type can be one of null, socket, udp, msmouse, vc, file, pipe, console, serial, pty, stdio, braille, tty, or parport. All character devices must have a unique identification string up to 127 characters long. It is used to identify the device in other related directives. For the complete description of all back-end's suboptions, see the manual page (man 1 qemu-kvm). A brief description of the available back-ends follows:

null

Creates an empty device which outputs no data and drops any data it receives.

stdio

Connects to QEMU's process standard input and standard output.

socket

Creates a two-way stream socket. If path is specified, a Unix socket is created:

qemu-kvm [...] -chardev \
socket,id=unix_socket1,path=/tmp/unix_socket1,server

The server suboption specifies that the socket is a listening socket.

If port is specified, a TCP socket is created:

qemu-kvm [...] -chardev \
socket,id=tcp_socket1,host=localhost,port=7777,server,nowait

The command creates a local listening (server) TCP socket on port 7777. QEMU will not block waiting for a client to connect to the listening port (nowait).

udp

Sends all network traffic from VM Guest to a remote host over the UDP protocol.

qemu-kvm [...] -chardev udp,id=udp_fwd,host=mercury.example.com,port=7777

The command binds port 7777 on the remote host mercury.example.com and sends VM Guest network traffic there.

vc

Creates a new QEMU text console. You can optionally specify the dimensions of the virtual console:

qemu-kvm [...] -chardev vc,id=vc1,width=640,height=480 -mon chardev=vc1

The command creates a new virtual console called vc1 of the specified size, and connects the QEMU monitor to it.

file

Logs all traffic from VM Guest to a file on VM Host Server. The path is required and will be created if it does not exist.

qemu-kvm [...] -chardev file,id=qemu_log1,path=/var/log/qemu/guest1.log

By default QEMU creates a set of character devices for serial and parallel ports, and a special console for QEMU monitor. You can, however, create your own character devices and use them for just mentioned purposes. The following options will help you:

-serial char_dev

Redirects the VM Guest's virtual serial port to a character device char_dev on VM Host Server. By default, it is a virtual console (vc) in graphical mode, and stdio in non-graphical mode. The -serial understands many suboptions. See the manual page man 1 qemu-kvm for their complete list.

You can emulate up to 4 serial ports. Use -serial none to disable all serial ports.

-parallel device

Redirects the VM Guest's parallel port to a device. This option supports the same devices as -serial.

[Tip]

With SUSE Linux Enterprise Server as a VM Host Server, you can directly use the hardware parallel port devices /dev/parportN where N is the number of the port.

You can emulate up to 3 parallel ports. Use -parallel none to disable all parallel ports.

-monitor char_dev

Redirects the QEMU monitor to a character device char_dev on VM Host Server. This option supports the same devices as -serial. By default, it is a virtual console (vc) in a graphical mode, and stdio in non-graphical mode.

For a complete list of available character devices back-ends, see the man page (man 1 qemu-kvm).

13.4. Networking in QEMU

Use the -net option to define a network interface and a specific type of networking for your VM Guest. Currently, SUSE supports the following options: none, nic, user, bridge, and tap. For a complete list of -net suboptions, see the manual page (man 1 qemu-kvm).

Supported -net Suboptions

none

Disables a network card emulation on VM Guest. Only the loopback lo network interface is available.

bridge

Uses a specified network helper to configure the TAP interface and attach it to a specified bridge. For more information, see Section 13.4.3, “Bridged Networking”.

nic

Creates a new Network Interface Card (NIC) and connects it to a specified Virtual Local Area Network (VLAN). For more information, see Section 13.4.1, “Defining a Network Interface Card”.

user

Specifies a user-mode networking. For more information, see Section 13.4.2, “User-mode Networking”.

tap

Specifies a bridged or routed networking. For more information, see Section 13.4.3, “Bridged Networking”.

13.4.1. Defining a Network Interface Card

Use -net nic to add a new emulated network card:

qemu-kvm [...] -net nic,vlan=11,macaddr=00:16:35:AF:94:4B2,\
model=virtio3,name=ncard14

1

Connects the network interface to VLAN number 1. You can specify your own number, it is mainly useful for identification purpose. If you omit this suboption, QEMU uses the default 0.

2

Specifies the Media Access Control (MAC) address for the network card. It is a unique identifier and you are advised to always specify it. If not, QEMU supplies its own default MAC address and creates a possible MAC address conflict within the related VLAN.

3

Specifies the model of the network card. Use -net nic,model=? to get the list of all network card models supported by QEMU on your platform:

Currently, SUSE supports the models rtl8139 and virtio.

13.4.2. User-mode Networking

The -net user option instructs QEMU to use a user-mode networking. This is the default if no networking mode is selected. Therefore, these command lines are equivalent:

qemu-kvm -hda /images/sles11sp1_base.raw
qemu-kvm -hda /images/sles11sp1_base.raw -net nic -net user

This mode is useful if you want to allow the VM Guest to access the external network resources, such as Internet. By default, no incoming traffic is permitted and therefore, the VM Guest is not visible to other machines on the network. No administrator privileges are required in this networking mode. The user-mode is also useful to do a 'network-booting' on your VM Guest from a local directory on VM Host Server.

The VM Guest allocates an IP address from a virtual DHCP server. VM Host Server (the DHCP server) is reachable at 10.0.2.2, while the IP address range for allocation starts from 10.0.2.15. You can use ssh to connect to VM Host Server at 10.0.2.2, and scp to copy files back and forth.

13.4.2.1. Command Line Examples

This section shows several examples on how to set up user-mode networking with QEMU.

Example 13.1. Restricted User-mode Networking

qemu-kvm [...] -net user1,vlan=12,name=user_net13,restrict=yes4

1

Specifies user-mode networking.

2

Connect to VLAN number 1. If omitted, defaults to 0.

3

Specifies a human readable name of the network stack. Useful when identifying it in the QEMU monitor.

4

Isolates VM Guest. It will not be able to communicate with VM Host Server and no network packets will be routed to the external network.


Example 13.2. User-mode Networking with Custom IP Range

qemu-kvm [...] -net user,net=10.2.0.0/81,host=10.2.0.62,dhcpstart=10.2.0.203,\
hostname=tux_kvm_guest4

1

Specifies the IP address of the network that VM Guest sees and optionally the netmask. Default is 10.0.2.0/8.

2

Specifies the VM Host Server IP address that VM Guest sees. Default is 10.0.2.2.

3

Specifies the first of the 16 IP addresses that the built-in DHCP server can assign to VM Guest. Default is 10.0.2.15.

4

Specifies the hostname that the built-in DHCP server will assign to VM Guest.


Example 13.3. User-mode Networking with Network-boot and TFTP

qemu-kvm [...] -net user,tftp=/images/tftp_dir1,bootfile=/images/boot/pxelinux.02

1

Activates a built-in TFTP (a file transfer protocol with the functionality of a very basic FTP) server. The files in the specified directory will be visible to a VM Guest as the root of a TFTP server.

2

Broadcasts the specified file as a BOOTP (a network protocol which offers an IP address and a network location of a boot image, often used in diskless workstations) file. When used together with tftp, the VM Guest can boot from network from the local directory on the host.


Example 13.4. User-mode Networking with Host Port Forwarding

qemu-kvm [...] -net user,hostfwd=tcp::2222-:22

Forwards incoming TCP connections to the port 2222 on the host to the port 22 (SSH) on VM Guest. If sshd is running on VM Guest, enter

ssh qemu_host -p 2222

where qemu_host is the hostname or IP address of the host system, to get a SSH prompt from VM Guest.


13.4.3. Bridged Networking

With the -net tap option, QEMU creates a network bridge by connecting the host TAP network device to a specified VLAN of VM Guest. Its network interface is then visible to the rest of the network. This method does not work by default and has to be explicitly specified.

First, create a network bridge and add a VM Host Server physical network interface (usually eth0) to it:

  1. Start YaST Control Center and select Network Devices+Network Settings.

  2. Click Add and select Bridge from the Device Type drop-down list in the Hardware Dialog window. Click Next.

  3. Choose whether you need a dynamically or statically assigned IP address, and fill the related network settings if applicable.

  4. In the Bridged Devices pane, select the Ethernet device to add to the bridge.

    Figure 13.2. Configuring Network Bridge with YaST

    Configuring Network Bridge with YaST

    Click Next. When asked about adapting an already configured device, click Continue.

  5. Click OK to apply the changes. Check if the bridge is created:

    tux@venus:~> brctl show
    bridge name bridge id          STP enabled  interfaces
    br0         8000.001676d670e4  no           eth0

13.4.3.1. Connecting to a Bridge Manually

Use the following example script to connect VM Guest to the newly created bridge interface br0. Several commands in the script are run via the sudo mechanism because they require root privileges.

[Note]

Make sure the tunctl and bridge-utils packages are installed on the VM Host Server. If not, install them with zypper in tunctl bridge-utils.

#!/bin/bash
bridge=br01
tap=$(sudo tunctl -u $(whoami) -b)2
sudo ip link set $tap up3
sleep 1s4
sudo brctl addif $bridge $tap5
qemu-kvm -m 512 -hda /images/sles11sp1_base.raw \
-net nic,vlan=0,model=virtio,macaddr=00:16:35:AF:94:4B \
-net tap,vlan=0,ifname=$tap6,script=no7,downscript=no
sudo brctl delif $bridge $tap8
sudo ip link set $tap down9
sudo tunctl -d $tap10

1

Name of the bridge device.

2

Prepare a new TAP device and assign it to the user who runs the script. TAP devices are virtual network devices often used for virtualization and emulation setups.

3

Bring up the newly created TAP network interface.

4

Make a 1 second pause to make sure the new TAP network interface is really up.

5

Add the new TAP device to the network bridge br0.

6

The ifname= suboption specifies the name of the TAP network interface used for bridging.

7

Before qemu-kvm connects to a network bridge, it checks the script and downscript values. If it finds the specified scripts on the VM Host Server file system, it runs the script before it connects to the network bridge and downscript after it exits the network environment. You can use these scripts to first set up and bring up the bridged network devices, and then to deconfigure them. By default, /etc/qemu-ifup and /etc/qemu-ifdown are examined. If script=no and downscript=no are specified, the script execution is disabled and you have to take care manually.

8

Deletes the TAP interface from a network bridge br0.

9

Sets the state of the TAP device to 'down'.

10

Deconfigures the TAP device.

13.4.3.2. Connecting to a Bridge with qemu-bridge-helper

Another way to connect VM Guest to a network through a network bridge is by means of the qemu-bridge-helper helper program. It configures the TAP interface for you, and attaches it to the specified bridge. The default helper executable is /usr/lib64/qemu-bridge-helper. The helper executable is setuid root, which is only executable by the members of the virtualization group (kvm). Therefore the qemu-kvm command itself does not have to be run under root privileges.

You can call the helper the following way:

qemu-kvm [...] -net nic,vlan=0,model=virtio -net bridge,vlan=0,br=br0

You can specify your own custom helper script that will take care of the TAP device (de)configuration, with the helper=/path/to/your/helper option:

qemu-kvm [...] -net bridge,vlan=0,br=br1,helper=/path/to/bridge-helper
[Tip]

To define access privileges to qemu-bridge-helper, inspect the /etc/qemu-kvm/bridge.conf file. For example the following directive

allow br0

allows the qemu-kvm command to connect its VM Guest to the network bridge br0.

13.4.4. Accelerated Networking with vhost-net

The vhost-net module is used to accelerate KVM's paravirtualized network drivers. It provides better latency and greater throughput for network.

To make use of the module, verify that the host's running Kernel has CONFIG_VHOST_NET turned on or enabled as a module:

grep CONFIG_VHOST_NET /boot/config-`uname -r`

Also verify that the guest's running Kernel has CONFIG_PCI_MSI enabled:

grep CONFIG_PCI_MSI /boot/config-`uname -r`

If both conditions are met, use the vhost-net driver by starting the guest with the following example command line:

qemu-kvm [...] -netdev tap,id=guest0,vhost=on,script=no
-net nic,model=virtio,netdev=guest0,macaddr=00:16:35:AF:94:4B

Note that guest0 is an identification string of the vhost-driven device.

13.5. Viewing a VM Guest with VNC

QEMU normally uses an SDL (a cross-platform multimedia library) window to display the graphical output of a VM Guest. With the -vnc option specified, you can make QEMU listen on a specified VNC display and redirect its graphical output to the VNC session.

[Tip]

When working with QEMU's virtual machine via VNC session, it is useful to work with the -usbdevice tablet option.

Moreover, if you need to use another keyboard layout than the default en-us, specify it with the -k option.

The first suboption of -vnc must be a display value. The -vnc option understands the following display specifications:

host:display

Only connections from host on the display number display will be accepted. The TCP port on which the VNC session is then running is normally a 5900 + display number. If you do not specify host, connections will be accepted from any host.

unix:path

The VNC server listens for connections on Unix domain sockets. The path option specifies the location of the related Unix socket.

none

The VNC server functionality is initialized, but the server itself is not started. You can start the VNC server later with the QEMU monitor. For more information, see Chapter 15, Administrating Virtual Machines with QEMU Monitor.

tux@venus:~> qemu-kvm [...] -vnc :5
(on the client:)
wilber@jupiter:~> vinagre venus:5905 &

Figure 13.3. QEMU VNC Session

QEMU VNC Session

13.5.1. Secure VNC Connections

The default VNC server setup does not use any form of authentication. In the previous example, any user can connect and view the QEMU VNC Session from any host on the network.

There are several levels of security which you can apply to your VNC client/server connection. You can either protect your connection with a password, use x509 certificates, use SASL authentication, or even combine some of these authentication methods in one QEMU command.

See Section A.2, “Generating x509 Client/Server Certificates” for more information about the x509 certificates generation. For more information about configuring x509 certificates on a VM Host Server and the client, see Section 7.2.2, “Remote TLS/SSL Connection with x509 Certificate (qemu+tls)” and Section 7.2.2.3, “Configuring the Client and Testing the Setup”.

The Vinagre VNC viewer supports advanced authentication mechanisms. Therefore, it will be used to view the graphical output of VM Guest in the following examples. For this example, let us assume that the server x509 certificates ca-cert.pem, server-cert.pem, and server-key.pem are located in the /etc/pki/qemu directory on the host, while the client's certificates are distributed in the following locations on the client:

/etc/pki/CA/cacert.pem
/etc/pki/libvirt-vnc/clientcert.pem
/etc/pki/libvirt-vnc/private/clientkey.pem

Example 13.5. Password Authentication

qemu-kvm [...] -vnc :5,password -monitor stdio

Starts the VM Guest graphical output on VNC display number 5 (usually port 5905). The password suboption initializes a simple password-based authentication method. There is no password set by default and you have to set one with the change vnc password command in QEMU monitor:

QEMU 0.12.5 monitor - type 'help' for more information
(qemu) change vnc password
Password: ****

You need the -monitor stdio option here, because you would not be able to manage the QEMU monitor without redirecting its input/output.


Figure 13.4. Authentication Dialog in Vinagre

Authentication Dialog in Vinagre

Example 13.6. x509 Certificate Authentication

The QEMU VNC server can use TLS encryption for the session and x509 certificates for authentication. The server asks the client for a certificate and validates it against the CA certificate. Use this authentication type if your company provides an internal certificate authority.

qemu-kvm [...] -vnc :5,tls,x509verify=/etc/pki/qemu

Example 13.7. x509 Certificate and Password Authentication

You can combine the password authentication with TLS encryption and x509 certificate authentication to create a two-layer authentication model for clients. Remember to set the password in the QEMU monitor after you run the following command:

qemu-kvm [...] -vnc :5,password,tls,x509verify=/etc/pki/qemu -monitor stdio

Example 13.8. SASL Authentication

Simple Authentication and Security Layer (SASL) is a framework for authentication and data security in Internet protocols. It integrates several authentication mechanisms, like PAM, Kerberos, LDAP and more. SASL keeps its own user database, so the connecting user accounts do not need to exist on VM Host Server.

For security reasons, you are advised to combine SASL authentication with TLS encryption and x509 certificates:

qemu-kvm [...] -vnc :5,tls,x509,sasl -monitor stdio

13.6. VirtFS: Sharing Folders between Host and Guests

VM Guests usually run in a separate computing space—they are provided their own memory range, dedicated CPUs, and file system space. Ability to share parts of VM Host Server's file system makes the virtualization environment more flexible by simplifying mutual data exchange. Network file systems, such as CIFS and NFS, have been the traditional way of sharing folders. But as they are not specifically designed for virtualization purposes, they suffer from major performance and feature issues.

KVM introduces a new and more optimized tool called VirtFS (sometimes referred to as a file system pass-through). VirtFS uses a paravirtual file system driver, which avoids converting the guest application file system operations into block device operations, and then again into host file system operations. VirtFS uses Plan-9 network protocol for communication between the guest and the host.

You can typically use VirtFS to

  • access a shared folder from several guests, or to provide guest-to-guest file system access.

  • replace the virtual disk as the root file system to which the guest's ramdisk connects to during the guest boot process

  • provide storage services to different customers from a single host file system in a cloud environment

13.6.1. Implementation

In QEMU, the implementation of VirtFS is facilitated by defining two types of devices:

  • virtio-9p-pci device which transports protocol messages and data between the host and the guest.

  • fsdev device which defines the export file system properties, such as file system type and security model.

Example 13.9. Exporting Host's Filesystem with VirtFS

qemu-kvm [...] -fsdev local,id=exp11,path=/tmp/2,security_model=mapped3
-device virtio-9p-pci,fsdev=exp14,mount_tag=v_tmp5

1

Identification of the file system to be exported.

2

Filesystem path on the host to be exported.

3

Security model to be used—mapped keeps the guest file system modes and permissions isolated from the host, while none invokes a pass-through security model in which permission changes on the guest's files are reflected on the host as well.

4

The exported file system ID defined before with -fsdev id= .

5

Mount tag used later on the guest to mount the exported file system.

Such an exported file system can be mounted on the guest like this

mount -t 9p -o trans=virtio v_tmp /mnt

where v_tmp is the mount tag defined earlier with -device mount_tag= and /mnt is the mount point where you want to mount the exported file system.


13.7. KSM: Sharing Memory Pages between Guests

Kernel SamePage Merging (KSM) is a Linux Kernel feature which merges identical memory pages from multiple running processes into one memory region. Because KVM guests run as processes under Linux, KSM provides the memory overcommit feature to hypervisors for more efficient use of memory. Therefore, if you need to run multiple virtual machines on a host with limited memory, KSM is the best solution for you.

To make use of KSM, do the following.

  1. Verify that KSM is enabled in your running Kernel:

    grep KSM /boot/config-`uname -r`
    CONFIG_KSM=y

    If KSM is enabled in the running Kernel, you will see the following files under the /sys/kernel/mm/ksm directory:

    ls -l /sys/kernel/mm/ksm
    total 0
    drwxr-xr-x 2 root root    0 Nov  9 07:10 ./
    drwxr-xr-x 6 root root    0 Nov  9 07:10 ../
    -r--r--r-- 1 root root 4096 Nov  9 07:10 full_scans
    -r--r--r-- 1 root root 4096 Nov  9 07:10 pages_shared
    -r--r--r-- 1 root root 4096 Nov  9 07:10 pages_sharing
    -rw-r--r-- 1 root root 4096 Nov  9 07:10 pages_to_scan
    -r--r--r-- 1 root root 4096 Nov  9 07:10 pages_unshared
    -r--r--r-- 1 root root 4096 Nov  9 07:10 pages_volatile
    -rw-r--r-- 1 root root 4096 Nov  9 07:10 run
    -rw-r--r-- 1 root root 4096 Nov  9 07:10 sleep_millisecs
  2. Check if KSM feature is turned on.

    cat /sys/kernel/mm/ksm/run

    If the command returns 0, turn KSM on with

    echo 1 > /sys/kernel/mm/ksm/run
  3. Now run several VM Guests under KVM and inspect the content of files pages_sharing and pages_shared, for example:

    while [ 1 ]; do cat /sys/kernel/mm/ksm/pages_shared; sleep 1; done
    13522
    13523
    13519
    13518
    13520
    13520
    13528

For more information on the meaning of the /sys/kernel/mm/ksm/* files, see /usr/src/linux/Documentation/vm/ksm.txt (package kernel-source).

Chapter 14. KVM Disk Cache Modes

14.1. Disk Interface Cache Modes

Qemu-kvm allows for various storage caching strategies to be specified when configuring a KVM guest. Each guest disk interface can have one of the following cache modes specified: writethrough, writeback, none, directsync, or unsafe. If no cache mode is specified, qemu-kvm uses an appropriate default cache mode. These cache modes influence how host based storage is accessed, as follows:

  • read/write data may be cached in the host page cache

  • the guest's storage controller is informed whether a write cache is present, allowing for the use of a flush command

  • synchronous write mode, in which write requests are reported complete only when committed to the storage device, may be used

  • flush commands (generated by the guest storage controller) may be ignored for performance reasons

In the event of an un-orderly disconnection between the guest and its storage, the cache mode in use will affect whether data loss occurs. The cache mode can also affect disk performance significantly. Additionally, some cache modes are incompatible with live migration, depending on a number of factors. There are no simple rules about what combination of cache mode, disk image format, image placement, or storage sub-system is best. The user should plan each guest's configuration carefully and experiment with various configurations to determine the optimal performance.

14.2. Description of Cache Modes

cache mode unspecified

In qemu-kvm versions older than v1.2 (eg SLES11 SP2), not specifying a cache mode meant that writethrough would be used as the default. Since that version, the various qemu-kvm guest storage interfaces have been fixed to handle writeback or writethrough semantics more correctly, allowing for the default caching mode to be switched to writeback. The guest driver for each of ide, scsi, and virtio have within their power to disable the write back cache, causing the caching mode used to revert to writethrough. The typical guest's storage drivers will maintain the default caching mode as writeback, however.

cache = writethrough

This mode causes qemu-kvm to interact with the disk image file or block device with O_DSYNC semantics, where writes are reported as completed only when the data has been committed to the storage device. The host page cache is used in what can be termed a writethrough caching mode. The guest's virtual storage adapter is informed that there is no writeback cache, so the guest would not need to send down flush commands to manage data integrity. The storage behaves as if there is a writethrough cache.

cache = writeback

This mode causes qemu-kvm to interact with the disk image file or block device with neither O_DSYNC nor O_DIRECT semantics, so the host page cache is used and writes are reported to the guest as completed when placed in the host page cache, and the normal page cache management will handle commitment to the storage device. Additionally, the guest's virtual storage adapter is informed of the writeback cache, so the guest would be expected to send down flush commands as needed to manage data integrity. Analogous to a raid controller with RAM cache.

cache = none

This mode causes qemu-kvm to interact with the disk image file or block device with O_DIRECT semantics, so the host page cache is bypassed and I/O happens directly between the qemu-kvm userspace buffers and the storage device. Because the actual storage device may report a write as completed when placed in its write queue only, the guest's virtual storage adapter is informed that there is a writeback cache, so the guest would be expected to send down flush commands as needed to manage data integrity. Equivalent to direct access to your hosts' disk, performance wise.

cache = unsafe

This mode is similar to the cache=writeback mode discussed above. The key aspect of this unsafe mode, is that all flush commands from the guests are ignored. Using this mode implies that the user has accepted the trade-off of performance over risk of data loss in the event of a host failure. Useful, for example, during guest install, but not for production workloads.

cache=directsync

This mode causes qemu-kvm to interact with the disk image file or block device with both O_DSYNC and O_DIRECT semantics, where writes are reported as completed only when the data has been committed to the storage device, and when it is also desirable to bypass the host page cache. Like cache=writethrough, it is helpful to guests that do not send flushes when needed. It was the last cache mode added, completing the possible combinations of caching and direct access semantics.

14.3. Data Integrity Implications of Cache Modes

cache = writethrough, cache = none, cache=directsync

These are the safest modes, and considered equally safe, given that the guest operating system is modern and well behaved, which means that it uses flushes as needed. If you have a suspect guest, use writethough, or directsync. Note that some file systems are not compatible with cache=none or cache=directsync, as they do not support O_DIRECT, which these cache modes relies on.

cache = writeback

This mode informs the guest of the presence of a write cache, and relies on the guest to send flush commands as needed to maintain data integrity within its disk image. This is a common storage design which is completely accounted for within modern filesystems. But it should be noted that because there is a window of time between the time a write is reported as completed, and that write being committed to the storage device, this mode exposes the guest to data loss in the unlikely event of a host failure.

cache = unsafe

This mode is similar to writeback caching except the guest flush commands are ignored, nullifying the data integrity control of these flush commands, and resulting in a higher risk of data loss due to host failure. The name unsafe should serve as a warning that there is a much higher potential for data loss due to a host failure than with the other modes. Note that as the guest terminates, the cached data is flushed at that time.

14.4. Performance Implications of Cache Modes

The choice to make full use of the page cache, or to write through it, or to bypass it altogether can have dramatic performance implications. Other factors which influence disk performance include the capabilities of the actual storage system, what disk image format is used, the potential size of the page cache and the IO scheduler used. Additionally, not flushing the write cache increases performance, but with risk, as noted above. As a general rule, high end systems typically perform best with cache = none, because of the reduced data copying that occurs. The potential benefit of having multiple guests share the common host page cache, the ratio of reads to writes, and the use of aio = native (see below) should also be considered.

14.5. Effect of Cache Modes on Live Migration

The caching of storage data and meta-data restricts the configurations which support live migration. Currently, only raw, qcow2 and qed image formats can be used for live migration. If a clustered file system is used, all cache modes support live migration. Otherwise the only cache mode which supports live migration on read/write shared storage is cache = none.

The libvirt management layer includes checks for migration compatibility based on a number of factors. If the guest storage is hosted on a clustered filesystem, is readonly or is marked sharable, then the cache mode is ignored when determining if migration can be allowed. Otherwise libvirt will not allow migration unless the cache mode is set to none. However, this restriction can be overridden with the unsafe option to the migration APIs, which is also supported by virsh, as for example in

virsh migrate --live --unsafe
[Tip]

cache = none is required for the IO mode setting aio = native. If another cache mode is used, then the IO mode will silently be switched back to the default aio = threads. Qemu-kvm implements the guest flush within the host by using fdatasync().

Chapter 15. Administrating Virtual Machines with QEMU Monitor

When QEMU is running, a monitor console is provided for performing interaction with the user. Using the commands available in the monitor console, it is possible to inspect the running operating system, change removable media, take screen shots or audio grabs and control several other aspects of the virtual machine.

15.1. Accessing Monitor Console

To access the monitor console from QEMU, press Ctrl+Alt+2. To return back to QEMU from the monitor console, press Ctrl+Alt+1.

To get help while using the console, use help or ?. To get help for a specific command, use help command.

15.2. Getting Information about the Guest System

To get information about the guest system, use the info option command. If used without any option, the list of possible options is printed. Options determine which part of the system will be analyzed:

info version

Shows the version of QEMU

info commands

Lists available QMP commands

info network

Shows the network state

info chardev

Shows the character devices

info block

Information about block devices, such as hard drives, floppy drives, or CD-ROMs

info blockstats

Read and write statistics on block devices

info registers

Shows the CPU registers

info cpus

Shows information about available CPUs

info history

Shows the command line history

info irq

Shows the interrupts statistics

info pic

Shows the i8259 (PIC) state

info pci

Shows the PCI information

info tlb

Shows virtual to physical memory mappings

info mem

Shows the active virtual memory mappings

info jit

Shows dynamic compiler information

info kvm

Shows the KVM information

info numa

Shows the NUMA information

info usb

Shows the guest USB devices

info usbhost

Shows the host USB devices

info profile

Shows the profiling information

info capture

Shows the capture (audio grab) information

info snapshots

Shows the currently saved virtual machine snapshots

info status

Shows the current virtual machine status

info pcmcia

Shows the guest PCMCIA status

info mice

Shows which guest mice is receiving events

info vnc

Shows the VNC server status

info name

Shows the current virtual machine name

info uuid

Shows the current virtual machine UUID

info usernet

Shows the user network stack connection states

info migrate

Shows the migration status

info balloon

Shows the balloon device information

info qtree

Shows the device tree

info qdm

Shows the qdev device model list

info roms

Shows the ROMs

info migrate_cache_sizes

Shows the current migration xbzrle (=Xor Based Zero Run Length Encoding) cache size.

info migrate_capabilities

Shows the status of the various migration capabilities, such as xbzrle compression.

info mtree

Shows the VM Guest memory hierarchy.

info trace-events

Shows available trace-events and their status.

15.3. Changing VNC Password

To change the VNC password, use the change vnc password command and enter the new password:

(qemu) change vnc password
Password: ********
(qemu)
    

15.4. Managing Devices

To release the device or file connected to the removable media device, use the eject device command. Use the optional -f to force ejection.

To change removable media (like CD-ROMs), use the change device command. The name of the removable media can be determined using the info block command:

(qemu) info block
ide1-cd0: type=cdrom removable=1 locked=0 file=/dev/sr0 ro=1 drv=host_device
(qemu) change ide1-cd0 /path/to/image
     

15.5. Controlling Keyboard and Mouse

It is possible to use the monitor console to emulate keyboard and mouse input if necessary. For example, if your graphical user interface intercepts some key combinations at low level (such as Ctrl+Alt+F1 in X Window), you can still enter them using the sendkey keys:

sendkey ctrl-alt-f1

To list the key names used in the keys option, enter sendkey and press Tab.

To control the mouse, the following commands can be used:

mouse_move dxdy [dz]

Move the active mouse pointer to the specified coordinates dx, dy with the optional scroll axis dz.

mouse_button val

Change the state of the mouse buttons (1=left, 2=middle, 4=right).

mouse_set index

Set which mouse device receives events. Device index numbers can be obtained with the info mice command.

15.6. Changing Available Memory

If the virtual machine was started with the -balloon virtio option and the paravirtualized balloon device that allows to dynamically change the amount of memory available is therefore enabled, it is possible to change the available memory dynamically. For more information about enabling the balloon device, see Section 12.1, “Basic Installation with qemu-kvm.

To get information about the balloon device in the monitor console and to determine whether the device is enabled, use the info balloon command:

(qemu) info balloon

If the balloon device is enabled, use the balloon memory_in_MB command to set the requested amount of memory:

(qemu) balloon 400

15.7. Dumping Virtual Machine Memory

To save the content of the virtual machine memory to a disk or console output, use the following commands:

memsave addrsizefilename

Saves virtual memory dump starting at addr of size size to file filename

pmemsave addrsizefilename

Saves physical memory dump starting at addr of size size to file filename-

x /fmtaddr

Makes a virtual memory dump starting at address addr and formatted according to the fmt string. The fmt string consists of three parameters countformatsize:

The count parameter is the number of items to be dumped.

The format can be x (hex), d (signed decimal), u (unsigned decimal), o (octal), c (char) or i (assembly instruction).

The size parameter can be b (8 bits), h (16 bits), w (32 bits) or g (64 bits). On x86, h or w can be specified with the i format to respectively select 16 or 32-bit code instruction size. is the number of the items to be dumped.

xp /fmtaddr

Makes a physical memory dump starting at address addr and formatted according to the fmt string. The fmt string consists of three parameters countformatsize:

The count parameter is the number of the items to be dumped.

The format can be x (hex), d (signed decimal), u (unsigned decimal), o (octal), c (char) or i (asm instruction).

The size parameter can be b (8 bits), h (16 bits), w (32 bits) or g (64 bits). On x86, h or w can be specified with thei format to respectively select 16 or 32-bit code instruction size. is the number of the items to be dumped.

15.8. Managing Virtual Machine Snapshots

[Warning]

Managing snapshots in QEMU monitor is not officially supported by SUSE yet. However, the information found in this section may be helpful in specific cases.

Virtual machine snapshots are snapshots of the complete virtual machine including the state of CPU, RAM, and the content of all writable disks. To use virtual machine snapshots, you must have at least one non-removable and writable block device using the qcow2 disk image format.

Snapshots are helpful when you need to save your virtual machine in a particular state. For example, after you configured network services on a virtualized server and want to quickly start the virtual machine in the same state that has been saved last. You can also create a snapshot after the virtual machine has been powered off to create a backup state before you try something experimental and possibly make VM Guest unstable. This section introduces the former case, while the latter is described in Section 12.2.3, “Managing Snapshots of Virtual Machines with qemu-img”.

The following commands are available for managing snapshots in QEMU monitor:

savevm name

Creates a new virtual machine snapshot under the tag name or replaces an existing snapshot.

loadvm name

Loads a virtual machine snapshot tagged name.

delvm

Deletes a virtual machine snapshot.

info snapshots

Prints information about available snapshots.

(qemu) info snapshots 
Snapshot list:
ID1       TAG2               VM SIZE3        DATE4          VM CLOCK5
1         booting                4.4M 2010-11-22 10:51:10   00:00:20.476
2         booted                 184M 2010-11-22 10:53:03   00:02:05.394
3         logged_in              273M 2010-11-22 11:00:25   00:04:34.843
4         ff_and_term_running    372M 2010-11-22 11:12:27   00:08:44.965

1

Unique identification number of the snapshot. Usually auto-incremented.

2

Unique description string of the snapshot. It is meant as a human readable version of the ID.

3

The disk space occupied by the snapshot. Note that the more memory is consumed by running applications, the bigger the snapshot is.

4

Time and date the snapshot was created.

5

The current state of the virtual machine's clock.

15.9. Suspending and Resuming Virtual Machine Execution

The following commands are available for suspending and resuming virtual machines:

stop

Suspends the execution of the virtual machine.

cont

Resumes the execution of the virtual machine.

system_powerdown

Sends an ACPI shutdown request to the machine. The effect is similar to the power button on a physical machine.

q or quit

Terminates QEMU immediately.

15.10. Live Migration

The live migration process allows to transmit any virtual machine from one host system to another host system without any interruption in availability. It is possible to change hosts permanently or just during a maintenance. It is recommended that the source and destination systems have the same architecture, however it is possible to migrate between hosts with AMD and Intel architectures.

The requirements for the live migration:

  • Live migration is only possible between VM Host Servers with the same CPU features. The only supported CPU model for migration is -cpu qemu64 (default) with no additional features specified.

  • No physical devices can be passed from host to guest.

  • The VM Host Server and VM Guest need to have proper timekeeping installed.

  • AHCI interface, virtfs feature, and the -mem-path command-line option are not compatible with migration.

  • Migration from SP3 to SP2 or SP1 hosted guests is not supported.

  • The virtual machine image must be accessible on both source and destination hosts. For example, it can be located on a shared NFS disk.

  • The image directory should be located in the same path on both hosts.

  • Both hosts must be located in the same subnet.  

  • The guest on the source and destination hosts must be started in the same way.  

The live migration process has the following steps:

  1. The virtual machine instance is running on the source host.

  2. The virtual machine is started on the destination host in the frozen listening mode. The parameters used are the same as on the source host plus the -incoming tcp:ip:port parameter, where ip specifies the IP address and port specifies the port for listening to the incoming migration. If 0 is set as IP address, the virtual machine listens on all interfaces.

  3. On the source host, switch to the monitor console and use the migrate -d tcp:destination_ip:port command to initiate the migration.

  4. To determine the state of the migration, use the info migrate command in the monitor console on the source host.

  5. To cancel the migration, use the migrate_cancel command in the monitor console on the source host.

  6. To set the maximum tolerable downtime for migration in seconds, use the migrate_set_downtime number_of_seconds command.

  7. To set the maximum speed for migration in bytes per second, use the migrate_set_speed bytes_per_second command.

Appendix A. Appendix

A.1. Installing Paravirtualized Drivers

A.1.1. Installing virtio Drivers for Microsoft Windows*

SUSE has developed virtio based drivers for Windows, which are available in the Virtual Machine Driver Pack (VMDP). See http://www.suse.com/products/vmdriverpack/ for more information on the VMDP. Installation instructions for the drivers are provided with the VMDP package.

A.2. Generating x509 Client/Server Certificates

In order to be able to create x509 client and server certificates you need to issue them by a Certificate Authority (CA). It is recommended to set up an independent CA that only issues certificates for libvirt.

  1. Set up a CA as described in Section “Creating a Root CA” (Chapter 17, Managing X.509 Certification, ↑Security Guide).

  2. Create a server and a client certificate as described in Section “Creating or Revoking User Certificates” (Chapter 17, Managing X.509 Certification, ↑Security Guide). The Common Name (CN) for the server certificate must be the full qualified hostname, the Common Name for the client certificate can be freely chosen. For all other fields stick with the defaults suggested by YaST.

    Export the client and server certificates to a temporary location (for example, /tmp/x509/) by performing the following steps:

    1. Select the certificate on the certificates tab.

    2. Choose Export+Export to File+Certificate and the Key Unencrypted in PEM Format, provide the Certificate Password and the full path and the filename under File Name, for example, /tmp/x509/server.pem or /tmp/x509/client.pem.

    3. Open a terminal and change to the directory where you have saved the certificate and issue the following commands to split it into certificate and key (this example splits the server key):

      csplit -z -f s_ server.pem '/-----BEGIN/' '{1}'
             mv s_00 servercert.pem
             mv s_01 serverkey.pem
    4. Repeat the procedure for each client and server certificate you would like to export.

  3. Finally export the CA certificate by performing the following steps:

    1. Switch to the Description tab.

    2. ChooseAdvanced+Export to File+Only the Certificate in PEM Format and enter the full path and the filename under File Name, for example, /tmp/x509/cacert.pem.

A.3. QEMU Command Line Options

A.3.1. Supported qemu-kvm Command Line Options

-alt-grab
-append ...
-audio-help
-balloon ...
-boot ...
-cdrom ...
-chardev ...
-clock
-cpu ...
-ctrl-grab
-d ...
-daemonize
-debugcon ...
-device [isa-serial|isa-parallel|isa-fdc|ide-drive| ide-hd|ide-cd|pci-assign|kvm-pci-assign|VGA| cirrus-vga|rtl8139|virtio-net-pci|virtio-blk-pci| virtio-balloon-pci|virtio-9p-pci|usb-hub|usb-ehci| usb-tablet|usb-storage|usb-mouse|usb-kbd|virtserialport| virtconsole|virtio-serial-pci|virtio-serial|sga|i 82559er|e1000|virtio-scsi-pci|scsi-cd|scsi-hd|scsi-generic| scsi-disk|scsi-block|pc-sysfw|pci-serial|pci-serial-2x| pci-serial-4x|ich9-ahci|piix-usb-uhci|usb-host|usb-serial |usb-wacom-tablet|usb_braille|usb-net|pci-ohci| piix4-usb-uhci|virtio-rng-pci]
-display ...
-drive if=[ide|floppy|virtio] format=[raw|qcow2|qed] snapshot=off ...
-echr ...
-enable-kvm
-fda/-fdb ...
-fsdev ...
-full-screen
-gdb ...
-global ...
-h
-hda/-hdb/-hdc/-hdd ...
-help
-incoming ...
-initrd ...
-kernel ...
-loadvm ...
-m ...
-machine [help|?|none|pc|pc-0.12|pc-0.14|pc-0.15|pc-i440fx-1.4]
-mem-path ...
-mem-prealloc
-mon ...
-monitor ...
-M [help|?|none|pc|pc-0.12|pc-0.14|pc-0.15|pc-i440fx-1.4]
-name ...
-netdev ...
-net [nic|user|tap|bridge|none] mode=[rtl8139|e1000|virtio]
-no-acpi
-nodefaults
-nodefconfig
-no-frame
-nographic
-no-hpet
-no-quit
-no-reboot
-no-shutdown
-no-user-config
-object
-parallel ...
-pidfile ...
-qmp ...
-readconfig ...
-rtc ...
-runas ...
-s
-S
-sandbox ...
-sdl
-serial ...
-smbios ...
-smp ...
-tdf
-usb
-usbdevice [disk|host|serial|braille|net|tablet|mouse]
-uuid ..
-version
-vga [std|cirrus|none]
-virtfs ...
-vnc ...
-watchdog ...
-watchdog-action ...
-writeconfig ...

A.3.1.1. Deprecated features

The use of boot=on for virtio disks is no longer needed since the BIOS used supports the virtio block interface directly. In fact, its usage may cause problems, and is now considered deprecated.

The use of ? as a parameter to -cpu, -soundhw, -device, -M, -machine, -d, and -clock is now considered deprecated. Use help instead.

The -tdf command line option is now considered deprecated. The unsupported -no-kvm-pit command line option is now considered deprecated.

The unsupported -no-kvm-pit-reinjection command line option is now considered deprecated.

The -pcidevice qemu-kvm command line option is no longer recognized. Use -device pci-assign instead.

The unsupported -device testdev command line option is no longer recognized. Use -device pc-testdev instead.

The unsupported -kvm-shadow-memory command line option is no longer recognized. Its function is now accessible via the kvm_shadow_mem= parameter to the -machine command line option.

The unsupported -no-kvm-irqchip command line option is now considered deprecated. Its function is now accessible via the kernel_irqchip= parameter to the -machine command line option.

The unsupported -osk qemu-kvm command line option is no longer recognized.

The unsupported -M mac qemu-kvm command line option is no longer recognized.

The unsupported -enable-nesting command line option is no longer recognized.

The unsupported -old-param command line option is no longer recognized.

The unsupported -semihosting command line option is no longer recognized.

The unsupported -nvram command line option is no longer recognized.

The unsupported cpu_set monitor command is no longer recognized.

The deprecated Windows drivers (win-virtio-drivers.iso) are no longer provided. The Virtual Machine Driver Pack is the supported way to get virtio drivers for Windows guests.

A.3.2. Unsupported qemu-kvm Command Line Options

The following qemu-kvm command line options are not supported by SUSE:

-acpitable ...
-add-fd ...
-bios ...
-bt ...
-chroot ...
-curses
-device [ipoctal232|sysbus-ohci|i82562|ccid-card-passthru| smbus-eeprom|nec-usb-xhci|hda-duplex|hda-output|cfi.pflash01 |ivshmem|usb-bot|lsi53c895a|ich9-usb-uhci2|ich9-usb-uhci6| q35-pcihost|ich9-usb-uhci5|ich9-usb-uhci3|i6300esb| isa-debug-exit|ne2k_pci|vfio-pci|usb-uas|ich9-usb-uhci4| ioh3420|isa-ide|esp|usb-ccid|ich9-usb-ehci2|pcnet| ich9-intel-hda|dc390|ich9-usb-ehci1|sysbus-ahci|hda-micro| pci-bridge|x3130-upstream|isa-cirrus-vga|ich9-usb-uhci1| pc-testdev|ne2k_isa|isa-vga|cs4231a|sysbus-fdc|gus|| vmware-svga||i82801b11-bridge|i82557a|i82557c|i82557b| i82801|AC97|am53c974|intel-hda||i82558a|i82558b|usb-audio| i82550|isa-debugcon|ib700|sb16|megasas|i82551| xio3130-downstream|vt82c686b-usb-uhci|tpci200|i82559a| i82559b|i82559c|xlnx,ps7-usb|SUNW,fdtwo|isa-applesmc| exynos4210-ehci-usb|mch|usb-bt-dongle]
-drive if=[scsi|mtd|pflash], snapshot=on, format=[anything besides from raw, qcow2, qed]
-dtb
-g ...
-icount ...
-iscsi ...
-L ...
-machine [q35|pc-q35-1.4|pc-1.3|pc-1.2|pc-1.1|pc-1.0|pc-0.13|pc-0.11|pc-0.10|isapc]
-M [q35|pc-q35-1.4|pc-1.3|pc-1.2|pc-1.1|pc-1.0|pc-0.13|pc-0.11|pc-0.10|isapc]
-mtdblock ...
-net [socket|dump] ...
-no-fd-bootchk
-no-kvm
-no-kvm-irqchip
-no-kvm-pit
-no-kvm-pit-reinjection
-numa ...
-option-rom ...
-pflash ...
-portrait
-prom-env ...
-qtest ...
-qtest-log ...
-rotate
-sd ...
-set ...
-show-cursor
-singlestep
-snapshot
-soundhw ...
-spice ...
-tb-size ...
-trace ...
-vga [vmware|qxl|xenfb]
-virtioconsole ...
-win2k-hack

A.3.3. Supported qemu-kvm monitor Command Line Options

The following qemu-kvm monitor command line options are supported by SUSE:

?
balloon target ...
block_resize ...
boot_set ...
[c|cont]
change device ...
cpu ...
delvm ...
device_add ...
device_del ...
drive_add ...
drive_del ...
dump_guest_memory ...
eject ...
gdbserver ...
help
info ...
loadvm ...
logfile ...
logitem ...
mce ...
memsave ...
migrate ...
migrate_set_cache_size ...
migrate_set_capability ...
migrate_set_downtime ...
migrate_set_speed ...
mouse_button ...
mouse_move ...
mouse_set ...
nmi ...
pci_add ...
pci_del ...
pmemsave ...
[p|print] ...
q
savevm ...
sendkey ...
stop
system_powerdown
system_reset
system_wakeup
usb_add ...
usb_del ...
watchdog_action ...
x ...
xp ...

A.3.4. Unsupported qemu-kvm monitor Command Line Options

The following qemu-kvm monitor command line options are not supported by SUSE:

acl_add ...
acl_policy ...
acl_remove ...
acl_reset ...
acl_show ...
block_job_cancel ...
block_job_complete ...
block_job_pause ...
block_job_resume ...
block_job_set_speed ...
block_passwd ...
client_migrate_info ...
close_fd ...
commit ...
drive_mirror ...
expire_password ...
hostfwd_add ...
hostfwd_remove ...
host_net_add ...
host_net_remove ...
i ...
migrate_cancel
nbd_server_add ...
nbd server_start ...
nbd_server_stop ...
netdev_add
netdev_del ...
o ...
pcie_aer_inject_error ...
ringbuf_read ...
ringbuf_write ...
screendump ...
set_link ...
set_password ...
singlestep ...
snapshot_blkdev ...
stopcapture ...
sum ...
trace_event ...
wavcapture ...

In addition to the listed human monitor commands above, a JSON-based monitor interface called QMP (Qemu Monitor Protocol) is provided which allows for a more programmatic and control-oriented interaction with the monitor. See /usr/share/doc/packages/kvm/qmp-commands.txt for details on executing QMP commands. Below is the list of QMP commands:

add_client
add-fd
balloon
block_passwd
block_resize
block_set_io_throttle
block-snapshot-sync
change
chardev-add
chardev-remove
client_migrate_info
closefd
cont
cpu
device_add
device_del
drive-mirror
eject
expire_password
getfd
human-monitor-command
inject-nmi
memsave
migrate
migrate_cancel
migrate-set-cache-size
migrate-set-capabilities
migrate_set_downtime
migrate_set_speed
netdev_add
netdev_del
pmemsave
qmp_capabilities
query-balloon
query-block
query-blockstats
query-chardev
query-commands
query-cpus
query-events
query-fdsets
query-kvm
query-mice
query-migrate
query-migrate-cache-size
query-name
query-pci
query-spice
query-status
query-uuid
query-version
query-vnc
quit
remove-fd
ringbuf-read
ringbuf-write
screendump
send-key
set_link
set_password
stop
system_powerdown
system_reset
system_wakeup
transaction
xen-save-devices-state
xen-set-global-dirty-flag

Appendix B. GNU Licenses

This appendix contains the GNU Free Documentation License version 1.2.

B.1. GNU Free Documentation License

Copyright (C) 2000, 2001, 2002 Free Software Foundation, Inc. 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.

0. PREAMBLE

The purpose of this License is to make a manual, textbook, or other functional and useful document "free" in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.

This License is a kind of "copyleft", which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.

We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.

1. APPLICABILITY AND DEFINITIONS

This License applies to any manual or other work, in any medium, that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. Such a notice grants a world-wide, royalty-free license, unlimited in duration, to use that work under the conditions stated herein. The "Document", below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as "you". You accept the license if you copy, modify or distribute the work in a way requiring permission under copyright law.

A "Modified Version" of the Document means any work containing the Document or a portion of it, either copied verbatim, or with modifications and/or translated into another language.

A "Secondary Section" is a named appendix or a front-matter section of the Document that deals exclusively with the relationship of the publishers or authors of the Document to the Document's overall subject (or to related matters) and contains nothing that could fall directly within that overall subject. (Thus, if the Document is in part a textbook of mathematics, a Secondary Section may not explain any mathematics.) The relationship could be a matter of historical connection with the subject or with related matters, or of legal, commercial, philosophical, ethical or political position regarding them.

The "Invariant Sections" are certain Secondary Sections whose titles are designated, as being those of Invariant Sections, in the notice that says that the Document is released under this License. If a section does not fit the above definition of Secondary then it is not allowed to be designated as Invariant. The Document may contain zero Invariant Sections. If the Document does not identify any Invariant Sections then there are none.

The "Cover Texts" are certain short passages of text that are listed, as Front-Cover Texts or Back-Cover Texts, in the notice that says that the Document is released under this License. A Front-Cover Text may be at most 5 words, and a Back-Cover Text may be at most 25 words.

A "Transparent" copy of the Document means a machine-readable copy, represented in a format whose specification is available to the general public, that is suitable for revising the document straightforwardly with generic text editors or (for images composed of pixels) generic paint programs or (for drawings) some widely available drawing editor, and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters. A copy made in an otherwise Transparent file format whose markup, or absence of markup, has been arranged to thwart or discourage subsequent modification by readers is not Transparent. An image format is not Transparent if used for any substantial amount of text. A copy that is not "Transparent" is called "Opaque".

Examples of suitable formats for Transparent copies include plain ASCII without markup, Texinfo input format, LaTeX input format, SGML or XML using a publicly available DTD, and standard-conforming simple HTML, PostScript or PDF designed for human modification. Examples of transparent image formats include PNG, XCF and JPG. Opaque formats include proprietary formats that can be read and edited only by proprietary word processors, SGML or XML for which the DTD and/or processing tools are not generally available, and the machine-generated HTML, PostScript or PDF produced by some word processors for output purposes only.

The "Title Page" means, for a printed book, the title page itself, plus such following pages as are needed to hold, legibly, the material this License requires to appear in the title page. For works in formats which do not have any title page as such, "Title Page" means the text near the most prominent appearance of the work's title, preceding the beginning of the body of the text.

A section "Entitled XYZ" means a named subunit of the Document whose title either is precisely XYZ or contains XYZ in parentheses following text that translates XYZ in another language. (Here XYZ stands for a specific section name mentioned below, such as "Acknowledgements", "Dedications", "Endorsements", or "History".) To "Preserve the Title" of such a section when you modify the Document means that it remains a section "Entitled XYZ" according to this definition.

The Document may include Warranty Disclaimers next to the notice which states that this License applies to the Document. These Warranty Disclaimers are considered to be included by reference in this License, but only as regards disclaiming warranties: any other implication that these Warranty Disclaimers may have is void and has no effect on the meaning of this License.

2. VERBATIM COPYING

You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3.

You may also lend copies, under the same conditions stated above, and you may publicly display copies.

3. COPYING IN QUANTITY

If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering more than 100, and the Document's license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.

If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.

If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a computer-network location from which the general network-using public has access to download using public-standard network protocols a complete Transparent copy of the Document, free of added material. If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public.

It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document.

4. MODIFICATIONS

You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:

  1. Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if there were any, be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that version gives permission.

  2. List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications in the Modified Version, together with at least five of the principal authors of the Document (all of its principal authors, if it has fewer than five), unless they release you from this requirement.

  3. State on the Title page the name of the publisher of the Modified Version, as the publisher.

  4. Preserve all the copyright notices of the Document.

  5. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.

  6. Include, immediately after the copyright notices, a license notice giving the public permission to use the Modified Version under the terms of this License, in the form shown in the Addendum below.

  7. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document's license notice.

  8. Include an unaltered copy of this License.

  9. Preserve the section Entitled "History", Preserve its Title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled "History" in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence.

  10. Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the "History" section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission.

  11. For any section Entitled "Acknowledgements" or "Dedications", Preserve the Title of the section, and preserve in the section all the substance and tone of each of the contributor acknowledgements and/or dedications given therein.

  12. Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers or the equivalent are not considered part of the section titles.

  13. Delete any section Entitled "Endorsements". Such a section may not be included in the Modified Version.

  14. Do not retitle any existing section to be Entitled "Endorsements" or to conflict in title with any Invariant Section.

  15. Preserve any Warranty Disclaimers.

If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version's license notice. These titles must be distinct from any other section titles.

You may add a section Entitled "Endorsements", provided it contains nothing but endorsements of your Modified Version by various parties--for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.

You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.

The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.

5. COMBINING DOCUMENTS

You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers.

The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.

In the combination, you must combine any sections Entitled "History" in the various original documents, forming one section Entitled "History"; likewise combine any sections Entitled "Acknowledgements", and any sections Entitled "Dedications". You must delete all sections Entitled "Endorsements".

6. COLLECTIONS OF DOCUMENTS

You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.

You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.

7. AGGREGATION WITH INDEPENDENT WORKS

A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an "aggregate" if the copyright resulting from the compilation is not used to limit the legal rights of the compilation's users beyond what the individual works permit. When the Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.

If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document's Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.

8. TRANSLATION

Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.

If a section in the Document is Entitled "Acknowledgements", "Dedications", or "History", the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.

9. TERMINATION

You may not copy, modify, sublicense, or distribute the Document except as expressly provided for under this License. Any other attempt to copy, modify, sublicense or distribute the Document is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.

10. FUTURE REVISIONS OF THIS LICENSE

The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See http://www.gnu.org/copyleft/.

Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License "or any later version" applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation.

ADDENDUM: How to use this License for your documents
   Copyright (c) YEAR YOUR NAME.
   Permission is granted to copy, distribute and/or modify this document
   under the terms of the GNU Free Documentation License, Version 1.2
   or any later version published by the Free Software Foundation;
   with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
   A copy of the license is included in the section entitled “GNU
   Free Documentation License”.
  

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with...Texts.” line with this:

   with the Invariant Sections being LIST THEIR TITLES, with the
   Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.
  

If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.


SUSE Linux Enterprise Server Virtualization with KVM 11 SP3