Bash Terminate Process

Sending Signals with kill

Despite the name, kill does not inherently destroy a process — it sends it a signal, and what happens next depends on that process's own signal handling. Run without any flag, kill sends signal 15 (SIGTERM), a polite request that well-behaved programs can catch and use to shut down cleanly, saving state or closing connections first.

$ ps aux | grep worker
alice     4521  0.4  0.3  98200 21400 pts/1    S    09:40   0:05 python3 worker.py
$ kill 4521
$ ps aux | grep worker
alice     4602  0.0  0.0   9032   980 pts/1    S+   09:44   0:00 grep worker

Common Signal Numbers

Linux defines dozens of signals, but a handful come up constantly in day-to-day shell work. Each has both a name and a number, and both forms are accepted by kill interchangeably.

kill -9: The Last Resort

kill -9 sends SIGKILL, which the kernel enforces directly without ever notifying the target process, so it cannot be caught, blocked, or ignored. That makes it effective against a genuinely frozen process, but it also skips any cleanup code the program would normally run, which can leave temporary files, lock files, or half-written database records behind.

$ kill -9 4521
$ ps -p 4521
PID TTY      TIME CMD

killall and pkill by Name

Looking up a PID first isn't always necessary. killall sends a signal to every process matching an exact program name, and pkill matches against a pattern, both accepting the same signal flags as kill.

$ killall -15 node
$ pkill -9 -f "worker.py --queue=default"