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3.5. Setting Cgroup Parameters

Modify the parameters of the control groups by editing the /etc/cgconfig.conf configuration file, or by using the cgset command. Changes made to /etc/cgconfig.conf are preserved after reboot, while cgset changes the cgroup parameters only for the current session.

Modifying /etc/cgconfig.conf

You can set the controller parameters in the Groups section of /etc/cgconfig.conf. Group entries are defined using the following syntax: 
group name {
[permissions]
    controller {
        param_name = param_value;
        …
    }
    …
}
Replace name with the name of your cgroup, controller stands for the name of the controller you wish to modify. You should modify only controllers you mounted yourself, not any of the default controllers mounted automatically by systemd. Replace param_name and param_value with the controller parameter you wish to change and its new value. Note that the permissions section is optional. To define permissions for a group entry, use the following syntax: 
perm {
    task {
        uid = task_user;
        gid = task_group;
    }
    admin {
       uid = admin_name;
       gid = admin_group;
    }
}

Note

Restart the cgconfig service for the changes in the /etc/cgconfig.conf to take effect. Restarting this service rebuilds hierarchies specified in the configuration file but does not affect all mounted hierarchies. You can restart a service by executing the systemctl restart command, however, it is recommended to first stop the cgconfig service: 
~]# systemctl stop cgconfig
Then open and edit the configuration file. After saving your changes, you can start cgconfig again with the following command: 
~]# systemctl start cgconfig

Using the cgset Command

Set controller parameters by running the cgset command from a user account with permission to modify the relevant cgroup. Use this only for controllers you mounted manually.
The syntax for cgset is: 
cgset -r parameter=value path_to_cgroup
where:
  • parameter is the parameter to be set, which corresponds to the file in the directory of the given cgroup;
  • value is the value for the parameter;
  • path_to_cgroup is the path to the cgroup relative to the root of the hierarchy.
The values that can be set with cgset might depend on values set higher in a particular hierarchy. For example, if group1 is limited to use only CPU 0 on a system, you cannot set group1/subgroup1 to use CPUs 0 and 1, or to use only CPU 1.
It is also possible use cgset to copy the parameters of one cgroup into another, existing cgroup. The syntax to copy parameters with cgset is: 
cgset --copy-from path_to_source_cgroup path_to_target_cgroup
where:
  • path_to_source_cgroup is the path to the cgroup whose parameters are to be copied, relative to the root group of the hierarchy;
  • path_to_target_cgroup is the path to the destination cgroup, relative to the root group of the hierarchy.