How to Kill a Process on Linux

Finding Processes to Kill

Before you can kill a process, you need its PID (Process ID). There are several ways to find it:

ps aux | grep firefox       # list all processes, filter by name
pgrep firefox               # print PIDs of matching processes
pidof nginx                 # print PID of a named program
top                         # interactive process list (q to quit)
htop                        # better interactive list (install: sudo apt install htop)

kill — Send a Signal by PID

The kill command sends a signal to a process. The default signal is SIGTERM (15), which asks the process to shut down gracefully:

kill 1234               # graceful shutdown (SIGTERM)
kill -9 1234            # force kill (SIGKILL) — no cleanup
kill -15 1234           # explicit SIGTERM

Always try kill PID first. Only use kill -9 if the process ignores the graceful signal — SIGKILL cannot be caught or ignored by the process.

killall — Kill by Name

killall kills all processes matching a name, saving you from finding PIDs:

killall firefox
killall -9 chrome         # force kill all Chrome processes
killall -u alice          # kill all processes owned by user alice

pkill — Kill by Pattern

pkill is like killall but matches against a pattern and supports more options:

pkill firefox
pkill -9 java
pkill -u bob              # kill all of bob's processes
pkill -f "python script.py"   # match against the full command line

Signals Explained

• SIGTERM (15) — politely ask the process to stop. Default signal.
• SIGKILL (9) — immediately terminate. Cannot be caught or ignored.
• SIGHUP (1) — reload config (many daemons respond to this)
• SIGINT (2) — same as pressing Ctrl+C in the terminal

Kill a Process Using the Most Port

Find what's listening on a port and kill it:

sudo lsof -i :3000          # find process on port 3000
sudo ss -tlnp | grep 3000   # alternative
# then kill the PID shown
kill 5678

Using top or htop

In top, press k, enter the PID, then choose a signal. In htop, select a process with arrow keys and press F9 to choose a signal, or F10 to quit.