systemd

Five stages, and which one you are stuck in tells you what to fix. A machine that reaches a GRUB prompt has a different problem from one that hangs waiting on a filesystem that no longer exists.

Most hand-written units boot in dev and die in production. The gap is Type selection, restart policy, and the drop-in workflow vendors expect you to respect.

Everyone knows ulimit -n. The interview question is which process inherits which value, why limits.conf did nothing for your service, and how you size the ceiling honestly.

Volatile by default on many distros, size-capped by silent policy, binary on disk. Know the storage modes, the vacuum knobs, and how journald feeds central logging.

Absolute caps versus latency-target protection, systemd IO attributes versus raw io.max, and why ionice lies to you. The staff-level answer assigns the job its own slice with intent.

Pod-level SIGTERM handling and node-level shutdown coordination are different mechanisms, and conflating them is the trap. The kubelet can only drain pods on power-off if it participates in systemd's shutdown sequence.

Emergency mode after a storage change is usually one line in fstab. The order of operations is what decides the outcome here, along with whether the recovery preserves data-mount dependencies rather than booting past them.

Everyone reaches for reinstall. The disciplined path is one journal file, four failure signatures, and an explicit decision about whether this host deserves surgery at all.

This one separates people who read journals from people who restart harder. The exit code and signal systemd already recorded usually name the disease.

The kill was not random and it was not fair. Learn the scoring function the kernel actually uses, then bend it with oom_score_adj before your monitoring dies during the next leak.