OOM killer event
also: OOM killer, Out-Of-Memory killer, memory pressure event
The Linux kernel's automatic process termination mechanism that frees memory by killing non-essential processes when the system runs critically low on available RAM.
When a Linux system exhausts available memory (RAM), the kernel's Out-Of-Memory (OOM) killer activates automatically to prevent a complete system crash. It selects and forcefully terminates one or more running processes to reclaim memory space.
The kernel uses a scoring algorithm (based on memory usage, priority, and other factors) to choose which process to kill. Processes with higher OOM scores are killed first. This is a last-resort mechanism—a running process receives no warning and cannot catch the termination signal.
You can monitor OOM killer events by checking kernel logs: dmesg | grep -i 'out of memory' or journalctl -p err. Production systems should be configured with sufficient memory or swap space to prevent OOM events, as they can cause unexpected data loss and service interruptions.
The OOM killer's behavior can be tuned via /proc filesystem parameters, and specific processes can be protected or prioritized for killing using the oom_score_adj setting.