How do I disable the systemd OOM process killer in Ubuntu 22.04?

Ubuntu 22.04 comes with the systemd-oomd service enabled by default, which has been "helpfully" killing my IDE and / or terminals whenever I try to compile an application using an abundance of threads / memory.

What is the right way to either turn this off, or configure the service to not shoot random processes in the face while I'm using them?

I'm aware that I can mitigate this behavior in a few ways; e.g. by increasing the size of the swap space, but this is still not a panacea since:

• The OOM daemon kills the entire process tree, so even the terminal hosting the processes that were killed will suddenly vanish;

• The OOM daemon kills the process tree without providing any notification to the user, so all the user knows is that their terminal / IDE / application hosting memory-hungry processes has suddenly vanished.

A user could find out what happened post-hoc via journalctl or something similar if they knew what to look for, but I don't think the average Ubuntu desktop user would think to do this.

As an example, normally when a process crashes via a deadly signal or similar, a crash reporter will tell the user that something went wrong. Shouldn't there be a similar facility for processes killed by the OOM daemon?

Edited to add requested output re: swap space; as far as I know these are just the defaults that were set when Ubuntu 22.04 was installed.

$ free -h total used free shared buff/cache available
Mem: 31Gi 5.2Gi 3.1Gi 210Mi 23Gi 25Gi
Swap: 2.0Gi 0.0Ki 2.0Gi
$ sysctl vm.swappiness
vm.swappiness = 60
$ swapon -s
Filename Type Size Used Priority
/swapfile file 2097148 792 -2

2 Answers

Most systemd services can be managed via the systemctl utility. In this case, we want to disable the systemd-oomd service. This can be done with:

$ systemctl disable --now systemd-oomd

You should see something like (depending on your OS):

$ systemctl disable --now systemd-oomd
Removed /etc/systemd/system/
Removed /etc/systemd/system/dbus-org.freedesktop.oom1.service.

You can then verify that the service is disabled, with:

$ systemctl is-enabled systemd-oomd

And you should then see:

$ systemctl is-enabled systemd-oomd
disabled

It is possible, however, that other services might attempt to restart the systemd-oomd service. To prevent this, you can 'mask' the service. For example:

$ systemctl mask systemd-oomd
Created symlink /etc/systemd/system/systemd-oomd.service → /dev/null.

And then systemctl is-enabled should now report:

$ systemctl is-enabled systemd-oomd
masked

See man systemctl for more details; in particular, note the caveats regarding masking of systemd services.

With 32G RAM, the default 2G /swapfile would normally be enough. However if you're running some large memory-hungry apps, or have large data-sets, it may need to swap more, so we'll increase it from 2G to 4G and see if that helps. Don't disable OOM.

Note: Incorrect use of the rm and dd commands can cause data loss. Suggest copy/paste.

In the terminal...

sudo swapoff -a # turn off swap
sudo rm -i /swapfile # remove old /swapfile
sudo dd if=/dev/zero of=/swapfile bs=1M count=4096
sudo chmod 600 /swapfile # set proper file protections
sudo mkswap /swapfile # init /swapfile
sudo swapon /swapfile # turn on swap
free -h # confirm 32G RAM and 4G swap

Edit /etc/fstab, using sudo -H gedit /etc/fstab or sudo pico /etc/fstab.

Confirm this /swapfile line in /etc/fstab... and confirm no other “swap” lines... use SPACES in this line... confirm NO TABS...

/swapfile none swap sw 0 0

reboot # reboot and verify operation