From Fedora Project Wiki


This test case tests that systemd-oomd kills the largest swap consumer when swap used is greater 90% (or whatever limit was defined by systemd-oomd-defaults).


  • This test case should be performed on either bare-metal or virtual machines.
  • Check that you are running systemd 248~rc4 or higher with systemctl --version.
  • Ensure the systemd-oomd-defaults package is installed (included with Fedora 34).
  • Boot the system and log in as a regular user.
  • Ensure no other conflicting userspace OOM killers are running. For example you may have to stop earlyoom:
sudo systemctl stop earlyoom

How to test

  • Check that systemd-oomd is running:
systemctl status systemd-oomd
  • Check that the systemd-oomd-defaults policy was applied by running oomctl and verifying that "/" is listed as a path under "Swap Monitored CGroups" along with the current swap usage.
  • Now run the test:
systemd-run --user -r --unit systoomd_swap_test tail /dev/zero
  • Make sure to reset the test unit after verifying the results:
systemctl --user reset-failed systoomd_swap_test.service

Expected Results

  • systemd-oomd will have killed the unit started above.
  • You can verify by checking for some of the relevant log lines with journalctl: "Swap used <...> is more than 90%" or "systemd-oomd killed <...> process(es)"
  • The output of systemctl --user status systoomd_swap_test should say the unit is killed. The kill can be racy so you may or may not see "systemd-oomd killed <...> process(es) in this unit". But if you see that message and also mention of "oom-kill" (which means the kernel OOM killer also kicked in) please note that in the comments/results. Otherwise, if it was a systemd-oomd only kill there will be no mention of "oom-kill".
  • Swap used should be below 90% (use free -h)