How to migrate from libcgroup resource control setting to systemd unit setting.

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Environment

SUSE Linux Enterprise Server 12 Service Pack 1 (SLES 12 SP1)
SUSE Linux Enterprise Server 12 Service Pack 2 (SLES 12 SP2)

Situation

Systemd overwrites libcgroup settings from /etc/cgconfig.conf.

Resolution

The libcgroup resource control configuration file is in /etc/cgconfig.conf, however libcgroup is obsolete and it may conflict with systemd's own cgroup handling. The settings can be moved from /etc/cgconfig.conf to systemd unit configuration files.

If the program that requires cgroup settings does not have a systemd unit file yet, creating a new one, for example /etc/systemd/system/example.service, that includes the appropriate resource control statements is necessary.

For example, if the settings in /etc/cgconfig.conf are looking like this:

group cpu-grp {

cpu {

cpu.cfs_quota_us=40000;

cpu.cfs_period_us=100000;

}

the new or editied unit file /etc/systemd/system/example.service to start a program /opt/bin/quota40-app with quotas might look like this:

[Unit]

Description=Starting quota40-app with a CPU quota of 40%

[Service]

Type=simple

ExecStart=/opt/bin/quota40-app

CPUQuota=40%

The statement CPUQuota=40% sets the cpu quota to 40% (cfs_quota_us divided by cf_period_us multiplied by 100). The program can then be started by running systemctl start example.service.

If a program already has a service file, instead of editing the existing one drop-ins can be used for additional settings such as quotas. For drop-ins, a subdirectory for the service needs to be created, for example /etc/systemd/system/example.service.d/, and a files with names ending on .conf, for example 10-resource-control.conf can be created in it to set the additional directives for the service. Implementing above settings, /etc/systemd/system/example.service.d/10-resource-control.conf would look simply like this:

[Service]
CPUQuota=40%

Cause

Resource control specification is different between systemd and libcgroup, and there can be only one of them interacting with cgroup controllers.

Additional Information

The man page systemd.resource-control provides documentation for the various possible resource control settings in systemd to help transitioning from libcgroup.

Disclaimer

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