Limiting CPU and Memory on User Login Sessions with Systemd

On multiuser Linux systems you may need to limit the memory and CPU use of interactive users so that one user cannot hog or crash the box. There’s several ways to do this, but I find the systemd approach to be the cleanest. On older systems like RHEL 7 you can still use cgroups with the cgred approach, and on really old systems there is still ulimit

This approach uses a template for the systemd slice that a user’s login session is added to on login. This allows you to use standard systemd resource controls as defined in the systemd documentation

At /etc/systemd/system/user-.slice.d/50-userlimits.conf create the following (adjust values to taste):

[Slice]
MemoryMax=50G
CPUQuota=400%

For a given user UID, you can then check some stats, including memory usage, on their slice using systemctl - for example:

systemctl status user-12345.slice

Tested on RHEL 8 and 9.