Memory, swap and the OOM killer

Not running Starting usually ~20 s

Step 9 of 9 · summary · 2 min

Summary

In free -h, free is memory used for nothing; available is how much can be given to processes, counting the cache the kernel will drop.
Reading files grows buff/cache and barely changes available.
Without swap, process data lives only in RAM; when it runs out, the OOM killer ends a process with SIGKILL.
MemoryMax= is a service's memory ceiling: when the service hits it, journalctl -k has a Memory cgroup out of memory line, and the service gets Result=oom-kill.
Your own unit settings go into a drop-in in /etc/systemd/system/<unit>.d/ plus systemctl daemon-reload.
The preview service from the start of the lesson restarted in a loop: the panorama and its copy did not fit into its 64 MiB ceiling, although the machine had about 300 MiB available.

Ubuntu 24.04