How do you send signals to processes with kill, killall, and pkill?

kill targets by PID, killall by exact process name, pkill by name pattern or attribute (user, terminal) — all send SIGTERM by default.

Despite the scary name, kill doesn't only kill — it sends a signal, and SIGTERM (terminate) is merely its default. The three commands differ only in how they pick the targets:

kill command:

kill PID              # Send SIGTERM (15)
kill -9 PID           # Send SIGKILL (force)
kill -l               # List all signals
kill -HUP PID         # Send SIGHUP (reload config)

killall command:

killall firefox       # Kill all firefox processes
killall -9 firefox    # Force kill all

pkill command (more flexible):

pkill firefox         # Kill by name pattern
pkill -u john         # Kill all processes by user
pkill -t pts/1        # Kill processes on terminal
pkill -9 -u john      # Force kill user's processes

Warning: Always try SIGTERM first, SIGKILL only as last resort (allows no cleanup)!