linux · medium

Processes & Signals — ps, kill, jobs, systemctl

Process & signal basics: ps -ef vs ps aux (and Z=zombie); SIGTERM (clean, catchable) vs SIGKILL (uncatchable, skips cleanup) plus HUP/USR1; and systemctl + journalctl for real services instead of nohup.

🔑 Key line

ps -ef (PPID) / ps aux (%CPU,STAT; Z=zombie). Signals: TERM(15) clean+catchable, KILL(9) uncatchable last-resort, HUP reload, USR1 app-defined. Real services: systemctl + journalctl -u -f.

The code

ps -ef        # every process + parent PID (PPID)
ps aux        # %CPU %MEM RSS STAT

kill -TERM 1234   # 15: polite, catchable -> clean shutdown (default)
kill -HUP  1234   #  1: reload config (by convention)
kill -USR1 1234   # 10: app-defined (e.g. bump log level)
kill -KILL 1234   #  9: uncatchable last resort -- NO cleanup

systemctl restart myapp ; journalctl -u myapp -f

What this lesson walks through

01List processes — and spot a zombie
02The signals that matter
03Real services use systemd

ps aux / ps -ef list processes; STAT 'Z' (zombie) means the child exited but the parent never wait()ed for it.

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