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Linux ENOMEM (errno 12) — Cannot Allocate Memory (Deep Dive)

Criticalerrno

Overview

Deep dive into Linux ENOMEM covering OOM killer behavior, overcommit settings, memory cgroups, swap exhaustion, and kernel memory allocation failures.

Key Details

  • ENOMEM can come from user-space malloc failure or kernel-space allocation failure
  • Linux overcommit memory by default (vm.overcommit_memory=0), so ENOMEM is rare until truly out
  • When physical RAM + swap is exhausted, OOM killer selects a process to kill
  • OOM killer logs in dmesg: 'Out of memory: Kill process [PID] (name) score [N]'
  • Memory cgroups can impose per-container or per-service memory limits triggering ENOMEM earlier

Common Causes

  • Physical RAM + swap completely exhausted (system-wide OOM)
  • Memory cgroup limit reached (container/service-level OOM)
  • Memory leak in application consuming ever-increasing memory
  • Kernel memory (slab, page tables) exhausted despite user-space memory available
  • vm.overcommit_memory=2 (no overcommit) and commit limit reached

Steps

  1. 1Check memory usage: free -h to see RAM and swap status
  2. 2Check OOM killer activity: dmesg | grep -i 'out of memory' or 'oom-killer'
  3. 3Find memory hogs: ps aux --sort=-%mem | head -20
  4. 4Add swap space temporarily: sudo fallocate -l 4G /swapfile && sudo chmod 600 /swapfile && sudo mkswap /swapfile && sudo swapon /swapfile
  5. 5Check cgroup limits: cat /sys/fs/cgroup/memory/memory.limit_in_bytes (cgroup v1) or memory.max (v2)

Tags

linuxenomemerrno-12oom-killermemory

More in Errno

linux-errno-1-epermLinux errno 1 (EPERM) — Operation Not Permitted
Warning
linux-errno-2-enoentLinux errno 2 (ENOENT) — No Such File or Directory
Warning
linux-errno-5-eioLinux errno 5 (EIO) — Input/Output Error
Error
linux-errno-11-eagainLinux errno 11 (EAGAIN) — Resource Temporarily Unavailable
Informational
linux-errno-12-enomemLinux errno 12 (ENOMEM) — Out of Memory
Critical
linux-errno-13-eaccesLinux errno 13 (EACCES) — Permission Denied
Warning

Frequently Asked Questions

Linux overcommits memory. The OOM killer kills processes when memory is truly exhausted, rather than returning ENOMEM at allocation time.