23

How can I create and use cgroups as a non-root user?

For example, can I, entirely as a non-root user:

  • create a cgroup with access to one CPU
  • create a new process in that cgroup

?

I first asked here but I didn't receive a complete answer. I also asked on stackoverflow, but the question was closed as off topic.

19

You can't do that as a normal user. But you can setup a cgroup as root, and make it configurable by your user.

If you do not already have the default cgroups controllers mounted by e.g. systemd:

$ sudo mount -t tmpfs cgroup_root /sys/fs/cgroup
$ sudo mkdir /sys/fs/cgroup/cpuset
$ sudo mount -t cgroup -o cpuset cpuset /sys/fs/cgroup/cpuset

Create a cgroup:

$ sudo mkdir /sys/fs/cgroup/cpuset/${USER}
$ sudo chown -R ${USER} /sys/fs/cgroup/cpuset/${USER}

You can now modify the configuration of your cgroup as a normal user:

$ echo 0-3 > /sys/fs/cgroup/cpuset/${USER}/cpuset.cpus

Add a process to that group:

$ ./my_task &
$ echo $! > /sys/fs/cgroup/cpuset/${USER}/tasks

Or create a subgroup:

$ mkdir /sys/fs/cgroup/cpuset/${USER}/subgroup
$ echo 0-1 > /sys/fs/cgroup/cpuset/${USER}/subgroup/cpuset.cpus
$ ./my_other_task &
$ echo $! > /sys/fs/cgroup/cpuset/${USER}/subgroup/tasks
3
  • how would you delete the subgroup? rm -r fails for me
    – hbogert
    Jun 11 '16 at 15:34
  • 1
    rm -r would try to delete the files first, which fails. Use rmdir to remove a cgroup.
    – Dennis B.
    Jun 12 '16 at 15:59
  • You cannot rmdir until the tasks file is empty. root would need to look at the tasks file in the subgroup, and echo each pid there into the root cgroup's tasks file (/dev/cpuset/tasks on my RHEL 6.7 [kernel 2.6.32-358] box, but it looks like /sys/fs/cgroup/cpuset/tasks might by appropriate here).
    – Mike S
    Dec 12 '17 at 22:25
1

If you're using Ubuntu you (the root user) can install cgroup-lite and add what you need to /etc/cgconfig.conf, including which user(s) can change the cgroup's configuration. It runs on boot.

Failing that you (the root user) could add your own script to run during boot.

0

There is a series of articles on LWN on cgroups, see part 1, or look though the search there. Systemd includes a set of helpers to manage (processes caged by) cgroups.

2
0

In theory you should be able to run processes in transient (temporary) cgroups, e.g.

$ systemd-run --user --scope /bin/bash

but in reality, systemd is broken in many Linux distributions and that fails with something like

polkitd(authority=local)[1300]: Registered Authentication Agent for unix-process:10428:26722972 (system bus name :1.478 [/usr/bin/pkttyagent --notify-fd 5 --fallback], object path /org/freedesktop/PolicyKit1/AuthenticationAgent, locale en_DK.utf8)
systemd[2601]: run-rbe547d13ad2c41d7857ea9e660e51ab9.scope: Failed to add PIDs to scope's control group: Permission denied
systemd[2601]: run-rbe547d13ad2c41d7857ea9e660e51ab9.scope: Failed with result 'resources'.
systemd[2601]: Failed to start /bin/bash.
polkitd(authority=local)[1300]: Unregistered Authentication Agent for unix-process:10428:26722972 (system bus name :1.478, object path /org/freedesktop/PolicyKit1/AuthenticationAgent, locale en_DK.utf8) (disconnected from bus)

I don't know the exact reason for this failure but until this bug is fixed, you need root access to be able to configure control groups (cgroup).

5
  • Interesting. What distributions did this fail on? Sep 4 at 13:49
  • I'm currently running Ubuntu 18.04 LTS. I know it used to fail with older versions, too, but I haven't tested if it works in more recent version. It appears that it's missing fixes to bug github.com/systemd/systemd/issues/9512 – note that without sudo you probably don't want --scope but --pty. Sep 4 at 13:55
  • Works for me on 248, no sudo or --pty needed. I wonder why Ubuntu hasn't backported it? Did nobody open a bug in launchpad? Sep 4 at 15:26
  • It seems that the problem was the hack called snap by Canonical. It didn't support cgroupv2 until recently so Ubuntu postponed the switch until snap could work with newer API. This should work with Ubuntu 21.10 or greater according to documentation. Sep 4 at 15:29
  • If mount | grep cgroupv2 outputs something, you're running recent enough system. Sep 4 at 15:30

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