The sshd service easily reaches the TasksMax limit after disabling "UsePAM" in sshd_config

This document (000020981) is provided subject to the disclaimer at the end of this document.


SUSE Linux Enterprise Server 15 (All Service Packs)
SUSE Linux Enterprise Server 12 (All Service Packs)
SUSE Linux Enterprise Server for SAP Applications 15 (All Service packs)
SUSE Linux Enterprise Server for SAP Applications 12 (All Service packs)


An administrator has remarked out  "UsePAM" in /etc/ssh/sshd_config (or set "UsePAM no").   After running for a period of time, more and more tasks are counted under the slice of sshd.service.  Eventually, sshd.service reaches its Tasks limit:
# /bin/systemctl status sshd.service
● sshd.service - OpenSSH Daemon
   Loaded: loaded (/usr/lib/systemd/system/sshd.service; enabled; vendor preset: disabled)
 Main PID: 5246 (sshd)
    Tasks: 65536(limit: 65536)
   Memory: 48.5G
      CPU: 6.506s
   CGroup: /system.slice/sshd.service
           ├─ 4352 app-daemon -d
           ├─ 5092 sshd: cmhop [priv]  
           ├─ 5188 sshd: cmhop@pts/0   
           ├─ 5191 -bash

   sshd-gen-keys-start[10394]: Checking for missing server keys in /etc/ssh...
   sshd-gen-keys-start[10394]: /usr/sbin/sshd-gen-keys-start: fork: retry: No child processes

New ssh connections will be rejected and sshd.service fails to restart.


Raise the TasksMax limit for sshd.service.

In a default configuration, most SLES 12 and 15 installations have no limit on sshd.service tasks.  However, if administrators have set their own limits, then this problem may be encountered.  The limit of 65536 shown above in the "Situation" section is not the default limit.

Normally, the original limit is set to "infinity" within /usr/lib/systemd/system/sshd.service and that file should not be modified (except by installation of a different openssh package version).
sles15# grep TasksMax /usr/lib/systemd/system/sshd.service
Some administrators may have modified this anyway, so it should be checked.

The more common and appropriate location to customize this setting would be within the directory:

Within that directory, one or more files may have been created and may hold settings to override the original configuration.  These are called "drop in" files.  For example:
sles15:/ grep -H TasksMax /etc/systemd/system/sshd.service.d/*
If a limit is found within a certain file, that file can be edited and the limit raised.

If UsePAM has been disabled in /etc/ssh/sshd_config, TasksMax will likely need to be set very high (or to "infinity").  Of course, another potential solution is to enable "UsePam yes" again.


When UsePAM is disabled, "" is not loaded when sshd initiates a new ssh client process. Therefore, no new systemd session will be created.  All ssh connections and all programs run within them will be counted as tasks under the single slice of sshd.service.

Disabling "" in /etc/pam.d/common-session will cause the same problem.

Additional Information

The currently effective setting of TasksMax for sshd.service can be found with the following command.  The default configuration of "infinity" results in an extremely high value, as shown here:
 sles15:/ # systemctl show 'sshd.service' | grep TasksMax

Some very early SLES 12 distributions (for example SLES 12 SP0, maybe SP1), especially without maintenance updates applied, may show lower TasksMax limits for sshd.service and many other services.  Most TasksMax limits were too low when SLES 12 first shipped, but that was soon rectified.


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:000020981
  • Creation Date: 21-Feb-2023
  • Modified Date:07-Mar-2023
    • SUSE Linux Enterprise Server
    • SUSE Linux Enterprise Server for SAP Applications

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