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2.9. Starting a Process in a Control Group

Important — Mandatory parameters

Some subsystems have mandatory parameters that must be set before you can move a task into a cgroup which uses any of those subsystems. For example, before you move a task into a cgroup which uses the cpuset subsystem, the cpuset.cpus and cpuset.mems parameters must be defined for that cgroup.
The examples in this section illustrate the correct syntax for the command, but only work on systems on which the relevant mandatory parameters have been set for any controllers used in the examples. If you have not already configured the relevant controllers, you cannot copy example commands directly from this section and expect them to work on your system.
Refer to Section 3.10, “Additional Resources” for a description of which parameters are mandatory for given subsystems.
Launch processes in a cgroup by running the cgexec command. For example, this command launches the lynx web browser within the group1 cgroup, subject to the limitations imposed on that group by the cpu subsystem:
~]# cgexec -g cpu:group1 lynx http://www.redhat.com
The syntax for cgexec is: cgexec -g subsystems:path_to_cgroup command arguments , where:
You can also add the --sticky option before the command to keep any child processes in the same cgroup. If you do not set this option and the cgred daemon is running, child processes will be allocated to cgroups based on the settings found in /etc/cgrules.conf. The process itself, however, will remain in the cgroup in which you started it.

Alternative method

When you start a new process, it inherits the group of its parent process. Therefore, an alternative method for starting a process in a particular cgroup is to move your shell process to that group (refer to Section 2.8, “Moving a Process to a Control Group”), and then launch the process from that shell. For example:
~]# echo $$ > /cgroup/lab1/group1/tasks
lynx
Note that after exiting lynx, your existing shell is still in the group1 cgroup. Therefore, an even better way would be:
~]# sh -c "echo \$$ > /cgroup/lab1/group1/tasks && lynx"

2.9.1. Starting a Service in a Control Group

You can start certain services in a cgroup. Services that can be started in cgroups must:
  • use a /etc/sysconfig/servicename file
  • use the daemon() function from /etc/init.d/functions to start the service
To make an eligible service start in a cgroup, edit its file in the /etc/sysconfig directory to include an entry in the form CGROUP_DAEMON="subsystem:control_group" where subsystem is a subsystem associated with a particular hierarchy, and control_group is a cgroup in that hierarchy. For example:
CGROUP_DAEMON="cpuset:daemons/sql"