What is the OOM Killer? – cPanel

Question

What is the OOM Killer, and how do I know if it was responsible for killing a process?

Answer

Linux's OOM (Out Of Memory) killer, is a mechanism that the Linux kernel employs when the system is critically low on memory. When your system runs out of memory, it is the job of the Linux OOM killer to sacrifice one or more processes in order to free up memory for the system when all else fails.

You can determine if a process was killed by reviewing your system logs:

Using Almalinux or CloudLinux

Connect to your server using SSH as the root user.
Run the following command to search your system log for OOM killer messages:
# grep -Ei "(out of memory|oom)" /var/log/messages* -A 1 | grep -i mysql

Using Ubuntu

Connect to your server using SSH as the root user.
Run the following command to search your system log for OOM killer messages:
# grep -Ei "(out of memory|oom)" /var/log/syslog* -A 1 | grep -i mysql

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