Table of Contents

The kill command sends a signal to one or more process IDs (PIDs).

Despite the name, it is not only for terminating processes. It can also request reloads, interrupt jobs, or trigger custom signal handlers.

Overview

Common signal usage:

  • SIGTERM (15): graceful stop request (default)
  • SIGKILL (9): immediate forced termination
  • SIGHUP (1): often used to reload configuration
  • SIGINT (2): interrupt signal (like Ctrl+C)

Syntax

kill [options] pid...

Command Quick Reference

Command Purpose
kill <pid> Send default signal (TERM)
kill -TERM <pid> Graceful terminate
kill -KILL <pid> Force terminate
kill -HUP <pid> Request reload behavior
kill -l List available signals

Core Workflows

Graceful Termination (Preferred)

kill 12345
kill -TERM 12345

Force Termination (Last Resort)

kill -KILL 12345

Use only when the process does not respond to TERM.

Signal Multiple Processes

kill -TERM 1234 5678 9012

View Signal Names

kill -l

Useful Options

Option Meaning
-s <signal> Specify signal by name
-SIGNAL Specify signal by shorthand
-l List signal names

Examples

kill -TERM 12345
kill -HUP 2211
kill -KILL 4242

Troubleshooting

Operation Not Permitted

You can only signal processes you own unless using elevated privileges.

sudo kill -TERM <pid>

No Such Process

The PID may have exited already or changed. Re-check with:

ps -fp <pid>

Best Practices

  1. Try TERM before KILL.
  2. Confirm target PID carefully to avoid affecting the wrong process.
  3. Use pgrep to locate PIDs reliably by name.
  4. Prefer service managers (systemctl) for managed services.
  • ps: Inspect processes by PID
  • pgrep: Find matching PIDs
  • pkill: Signal by process pattern
  • systemctl: Control systemd-managed services
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