RHEL 6 Resource Management - 2.5. Creating Cgroups

Red Hat Enterprise Linux 9 Essentials Book now available.

Purchase a copy of Red Hat Enterprise Linux 9 (RHEL 9) Essentials

Red Hat Enterprise Linux 9 Essentials Print and eBook (PDF) editions contain 34 chapters and 298 pages

2.5. Creating Cgroups

Use the cgcreate command to create cgroups. The syntax for cgcreate is: cgcreate -t uid:gid -a uid:gid -g subsystems:path , where:

-t (optional) — specifies a user (by user ID, uid) and a group (by group ID, gid) to own the tasks pseudofile for this control group. This user can add tasks to the control group.

Note — Removing tasks

Note that the only way to remove a task from a control group is to move it to a different control group. To move a task, the user must have write access to the destination control group; write access to the source control group is unimportant.
-a (optional) — specifies a user (by user ID, uid) and a group (by group ID, gid) to own all pseudofiles other than tasks for this control group. This user can modify the access that the tasks in this control group have to system resources.
-g — specifies the hierarchy in which the cgroup should be created, as a comma-separated list of the subsystems associated with those hierarchies. If the subsystems in this list are in different hierarchies, the group is created in each of these hierarchies. The list of hierarchies is followed by a colon and the path to the child group relative to the hierarchy. Do not include the hierarchy mount point in the path.

For example, the control group located in the directory /cgroup/cpu_and_mem/lab1/ is called just lab1 — its path is already uniquely determined because there is at most one hierarchy for a given subsystem. Note also that the group is controlled by all the subsystems that exist in the hierarchies in which the cgroup is created, even though these subsystems have not been specified in the cgcreate command — refer to Example 2.3, “cgcreate usage”.

Because all control groups in the same hierarchy have the same controllers, the child group has the same controllers as its parent.

Example 2.3. cgcreate usage

Consider a system where the cpu and memory subsystems are mounted together in the cpu_and_mem hierarchy, and the net_cls controller is mounted in a separate hierarchy called net. We now run:

cgcreate -g cpu,net_cls:/test-subgroup

The cgcreate command creates two groups named test-subgroup, one in the cpu_and_mem hierarchy and one in the net hierarchy. The test-subgroup group in the cpu_and_mem hierarchy is controlled by the memory subsystem, even though we did not specify it in the cgcreate command.

Alternative method

To create a child of the control group directly, use the mkdir command:

mkdir /cgroup/hierarchy/name/child_name

For example:

mkdir /cgroup/cpuset/lab1/group1

2.5. Creating Cgroups

Note — Removing tasks

Example 2.3. cgcreate usage

Alternative method