kill: Sending Signals

Kill is misnamed

kill doesn't always kill — it sends a signal. Different signals tell the process different things; the default is SIGTERM ("please shut down"). Programs that handle signals can clean up. The nuclear option, SIGKILL, can't be caught.

The signals you'll use

• kill PID — same as kill -TERM. Default. Polite shutdown.
• kill -INT PID — SIGINT. Same as Ctrl+C.
• kill -HUP PID — SIGHUP. Many daemons treat this as "reload your config" without restarting.
• kill -USR1 PID — application-defined. nginx uses it for log rotation, for example.
• kill -KILL PID or kill -9 PID — SIGKILL. Force kill, no cleanup. Last resort.
• kill -STOP PID / -CONT — pause and resume (like Ctrl+Z then fg).

kill by name

pkill firefox
pkill -f 'python myscript.py'        # match full command
killall Slack                          # macOS GUI apps

The escalation ladder

1. kill PID — politely.
2. Wait 5–10 seconds. Most well-behaved programs exit by now.
3. kill -KILL PID — only if SIGTERM was ignored.

Reaching for -9 immediately is a bad habit; the program can't flush buffers, close files, or release locks. Save it for wedged-process emergencies.