Frequently Asked Question

What is the OOM killer and how do I tell when it strikes?

When Linux exhausts both RAM and swap and cannot satisfy a memory request, the kernel invokes the Out-Of-Memory killer rather than letting the whole system deadlock. The OOM killer walks every running process, calculates a "badness" score from its size, runtime, and a tunable oom_score_adj in /proc/<PID>/, and sends SIGKILL to whichever scores highest. The aim is to free the most memory while sacrificing the least-important process.

The kill is silent from a user's point of view, the process just vanishes, but the kernel always logs it. Run dmesg | grep -i "killed process" or journalctl -k | grep -i oom to see entries like "Out of memory: Killed process 23456 (chromium)". The fix is one of: add RAM or swap, find and cap the leaking process, or protect critical services by writing a negative value (e.g. -1000) to their oom_score_adj, which makes the killer skip them.