systemd-udevd[5511]: Could not generate persistent MAC address for br0: No such file or directory

This document (000020260) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server for SAP Applications 15
SUSE Linux Enterprise Server 15
 

Situation

Having a setup with bridges and bonds, the following is written to the journal.log.
journalctl -b0 -u systemd-udevd | grep MAC
May 11 11:09:16 server15 systemd-udevd[1030]: Could not generate persistent MAC address for br0: No such file or directory
May 11 11:09:16 server15 systemd-udevd[1028]: Could not generate persistent MAC address for bond1: No such file or directory

Resolution

The message is harmless, it will not break anything. But to make the system not write the messages anymore. The following workaround can be used.

Create a systemd link file called /etc/systemd/network/98-default.link. Which matches on drivers and set the MACAddressPolicy to none.

Use ethtool -i <device> to expose the driver.
server15:~ # ethtool -i br0
driver: bridge
version: 2.3
firmware-version: N/A
expansion-rom-version:
bus-info: N/A
supports-statistics: no
supports-test: no
supports-eeprom-access: no
supports-register-dump: no
supports-priv-flags: no

server15:~ # ethtool -i bond1
driver: bonding
version: 3.7.1
firmware-version: 2
expansion-rom-version:
bus-info:
supports-statistics: no
supports-test: no
supports-eeprom-access: no
supports-register-dump: no
supports-priv-flags: no

In this example the file will look as follows:
server15:~ # cat /etc/systemd/network/98-default.link
[Match]
Driver=bonding bridge

[Link]
MACAddressPolicy=none

Cause

MACAddressPolicy=persistent is used by default.

For interfaces that doesn't have a persistent MAC address (most hardware should) a new MAC address is generated which is guaranteed to be the same on every boot for the given machine and the given device, but which is otherwise random. The option MACAddressPolicy=persistent enables this by default in /usr/lib/systemd/network/99-default.link.

This feature depends on ID_NET_NAME_* properties to exist for the link. On virtual interfaces (such as bridges, bonds, etc...) these properties are not set hence the generation of a persistent MAC address will fail with:
"Could not generate persistent MAC address for $name: No such file or directory"
See for more information "man systemd.link"

Disclaimer

This Support Knowledgebase provides a valuable tool for SUSE customers and parties interested in our products and solutions to acquire information, ideas and learn from one another. Materials are provided for informational, personal or non-commercial use within your organization and are presented "AS IS" WITHOUT WARRANTY OF ANY KIND.

  • Document ID:000020260
  • Creation Date: 02-Jun-2021
  • Modified Date:02-Jun-2021
    • SUSE Linux Enterprise Server
    • SUSE Linux Enterprise Server for SAP Applications

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