Updated: 11 October 2026 · Applies to: AlmaLinux 9, Rocky Linux 9, Ubuntu 24.04 and Debian 12
The OOM (out of memory) killer is part of the Linux kernel. When the system runs out of memory and swap, it stops a process, usually the one using the most memory, to keep the server alive.
See what it did
dmesg -T | grep -i -E "out of memory|killed process" journalctl -k | grep -i oom
Prevent it
- Find what uses memory:
ps aux --sort=-%mem | head. - Tune memory-hungry services (for example database buffers or PHP-FPM children).
- Add swap as a safety net, or add RAM.
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