How to Use the kill Command in Linux: Syntax and Examples

Use the kill command followed by a process ID (PID) to send signals that stop or control processes in Linux. For example, kill 1234 sends the default TERM signal to stop process 1234 safely.

Syntax

The basic syntax of the kill command is:

• kill [options] <PID> - Sends a signal to the process with the given PID.
• -s <signal> or -<signal> - Specify which signal to send (e.g., TERM, KILL).
• -l - List all available signals.

Common signals include TERM (terminate gracefully) and KILL (force stop immediately).

bash

kill [options] <PID>

# Examples:
kill 1234
kill -9 1234
kill -s KILL 1234
kill -l

Example

This example shows how to find a process ID and stop it using kill. It demonstrates sending the default TERM signal and the forceful KILL signal.

bash

# Start a background process (sleep for 100 seconds)
sleep 100 &

# Get the PID of the sleep process
PID=$!

echo "Process ID is $PID"

# Send TERM signal to stop it gracefully
kill $PID

# Check if process is still running
ps -p $PID

# If still running, force kill it
kill -9 $PID

# Check again
ps -p $PID

Output

Process ID is 12345
  PID TTY          TIME CMD

# (No output after kill -9 means process stopped)

Common Pitfalls

Common mistakes when using kill include:

• Using the wrong PID or no PID, which results in errors or killing the wrong process.
• Not using sudo when trying to kill processes owned by other users.
• Using kill -9 (SIGKILL) too often, which stops processes immediately without cleanup.
• Confusing signal names and numbers.

Always try kill without -9 first to allow graceful shutdown.

bash

## Wrong way: Killing without PID
kill

## Right way: Specify PID
kill 1234

## Wrong way: Using kill -9 immediately
kill -9 1234

## Better way: Try TERM first
kill 1234
sleep 2
kill -9 1234

Output

kill: usage: kill [-s sigspec | -n signum | -sigspec] pid | jobspec ... or kill -l [sigspec]

# No output for correct kill commands

Quick Reference

Command	Description
kill	Send TERM signal to stop process gracefully
kill -9	Send KILL signal to force stop process immediately
kill -l	List all available signals
kill -s SIGINT	Send interrupt signal to process
kill -s SIGSTOP	Pause the process
kill -s SIGCONT	Resume a paused process

Key Takeaways

Use kill with the process ID to stop or control processes in Linux.

Try the default TERM signal before using the forceful KILL signal (-9).

Always verify the PID to avoid stopping the wrong process.

Use kill -l to see all available signals you can send.

Use sudo if you need permission to kill processes owned by other users.