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System 26 errors

Linux & System Errors

Disk space, systemd units, file descriptors, OOM killer and scheduled jobs.

Understanding System errors

System-level errors are usually a resource limit being hit: disk, inodes, file descriptors, memory or process count. Two traps recur. "No space left on device" can mean inodes are exhausted while df -h shows free space. And a process that vanished without an error in its own log was almost certainly killed by the OOM killer, which logs to the kernel ring buffer rather than to the application.

How to debug System errors

  1. Check both space and inodes: df -h and df -i. Millions of tiny files exhaust inodes long before bytes.
  2. For processes that disappear, search the kernel log: dmesg -T | grep -i -E 'oom|killed process' or journalctl -k.
  3. For systemd units, systemctl status unit then journalctl -u unit -n 200 --no-pager. The status output truncates the useful part.
  4. For "too many open files", check both the limit and the usage: ulimit -n, cat /proc/<pid>/limits, and ls /proc/<pid>/fd | wc -l. systemd services need LimitNOFILE, not a shell ulimit.
  5. For cron jobs that work manually but not scheduled, remember cron has a minimal environment and no PATH. Use absolute paths and log stdout and stderr to a file.

Tools worth reaching for

  • df -h / df -i
  • dmesg -T
  • journalctl -u
  • lsof / ss
  • systemd-analyze blame
  • ncdu

All 26 System errors

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