25.7. Viewing cgroups of processes

Procedure

1. To view which cgroup a process belongs to, run the # cat proc/<PID>/cgroup command:

   # cat /proc/2467/cgroup
   0::/system.slice/example.service

   The example output relates to a process of interest. In this case, it is a process identified by PID 2467, which belongs to the example.service unit. You can check if the process was placed in a correct control group as defined by the systemd unit file specifications.

2. To display what controllers and configuration files the cgroup uses, check the cgroup directory:

   # cat /sys/fs/cgroup/system.slice/example.service/cgroup.controllers
   memory pids
   
   # ls /sys/fs/cgroup/system.slice/example.service/
   cgroup.controllers
   cgroup.events
   …​
   cpu.pressure
   cpu.stat
   io.pressure
   memory.current
   memory.events
   …​
   pids.current
   pids.events
   pids.max

   The version 1 hierarchy of cgroups uses a per-controller model. Therefore the output from the /proc/PID/cgroup file shows, which cgroups under each controller the PID belongs to. You can find the cgroups under the controller directories at /sys/fs/cgroup/<controller_name>/.

   Refer to the /usr/share/doc/kernel-doc-<kernel_version>/Documentation/admin-guide/cgroup-v2.rst file (after installing the kernel-doc package) for more information.