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To resolve a cgroups issue where a process is being placed in the wrong cgroup, I'm being advised to take regular snapshots of the /proc/process-id/cgroups files over a period of time when the process is running. The idea being to identify the process and check if it's allocated cgroup is correct and/or changes over time.

Does anyone know of any tools which can capture this kind of information? I'm aware that simply 'tar'ing /proc isn't an option due to its nature.

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Even if it's virtual, it's just a text file:

grep . /proc/[0-9]*/cgroup | sort -V > snapshot.txt

This won't include process names (only PIDs) but that might be enough if you're trying to watch a long-running process, and it would be easy enough to get the command from /proc/…/exe or /proc/…/cmdline. You could possibly even 'tar' /proc if you carefully specified what to include.


Alternatively, if you want a tree output (with process names and everything):

systemd-cgls

(Best on cgroup v2 systems. On cgroup v1, systemd-cgls only captures 'name=systemd', not the other controllers.)

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