Code-Memo

Signals and process control

What are signals?

Signals are async notifications sent to processes (e.g., terminate, reload, stop).

Common signals

• SIGTERM (15): graceful stop (default for kill)
• SIGKILL (9): immediate stop (cannot be caught)
• SIGHUP (1): hangup; often means “reload config”
• SIGINT (2): interrupt (Ctrl+C)
• SIGSTOP / SIGTSTP: stop (cannot/can be caught)
• SIGCONT: continue

Sending signals

kill -TERM 1234
kill -KILL 1234
kill -HUP 1234

By name:

pkill -TERM nginx
killall -HUP nginx

Inspect signals / process state

ps -o pid,stat,cmd -p 1234
cat /proc/1234/status | grep -E 'State|Sig'

systemd and signals

Systemd usually sends SIGTERM then waits TimeoutStopSec and escalates.

Related

• Background and foreground jobs