kill Command Guide

Basic Usage

The kill command sends a signal to a process. By default, it sends SIGTERM (signal 15), which asks the process to terminate gracefully.

bash

# Terminate process by PID
kill 1234

# Same as above (explicit SIGTERM)
kill -15 1234
kill -TERM 1234

Common Signals

Frequently Used Signals

SIGTERM (15)	Graceful termination (default)
SIGKILL (9)	Force kill (cannot be caught)
SIGHUP (1)	Hangup - often used to reload config
SIGINT (2)	Interrupt (like Ctrl+C)
SIGSTOP (19)	Pause process
SIGCONT (18)	Continue paused process

bash

# List all available signals
kill -l

Graceful vs Force Kill

Graceful termination (SIGTERM)

Allows the process to clean up, save data, and exit properly.

bash

kill 1234

Force kill (SIGKILL)

Immediately terminates the process. Use only when SIGTERM doesn't work.

bash

kill -9 1234
# or
kill -KILL 1234

Warning

Always try kill (SIGTERM) first. Only use kill -9 when the process is unresponsive, as it doesn't allow cleanup.

Kill by Name: pkill and killall

pkill - pattern-based killing

bash

# Kill by process name
pkill nginx

# Kill by exact name
pkill -x nginx

# Kill processes owned by user
pkill -u username

# Force kill by name
pkill -9 nginx

killall - kill by exact name

bash

# Kill all processes with exact name
killall nginx

# Force kill all
killall -9 nginx

# Interactive mode (confirm each)
killall -i nginx

Tip

pkill matches partial names by default, while killall requires exact matches. Use pgrep first to verify which processes will be affected.

Finding Process IDs

bash

# Using pgrep
pgrep nginx
pgrep -a nginx  # Show full command line

# Using ps and grep
ps aux | grep nginx

# Using pidof
pidof nginx

Practical Examples

Kill multiple processes

bash

kill 1234 5678 9012

Kill all user processes

bash

pkill -u username

Reload configuration (HUP signal)

bash

# Reload nginx config
kill -HUP $(pgrep nginx)

# Or using pkill
pkill -HUP nginx

Pause and resume a process

bash

# Pause
kill -STOP 1234

# Resume
kill -CONT 1234

Kill unresponsive terminal process

bash

# From another terminal
ps aux | grep stuck_process
kill -9 <PID>

Kill all background jobs

bash

# In current shell
kill $(jobs -p)

Kill process tree

bash

# Kill process and all its children
pkill -P 1234    # Kill children
kill 1234        # Then kill parent

Safe Termination Pattern

Follow this pattern for safe process termination:

bash

# 1. Try graceful shutdown
kill <PID>

# 2. Wait a few seconds
sleep 5

# 3. Check if process is still running
ps -p <PID>

# 4. If still running, force kill
kill -9 <PID>

Signals Reference

All Common Signals

1 (SIGHUP)	Hangup - terminal closed or reload config
2 (SIGINT)	Interrupt from keyboard (Ctrl+C)
3 (SIGQUIT)	Quit from keyboard (Ctrl+\)
9 (SIGKILL)	Kill immediately (cannot be caught)
15 (SIGTERM)	Termination request (default)
18 (SIGCONT)	Continue stopped process
19 (SIGSTOP)	Stop process (cannot be caught)
20 (SIGTSTP)	Stop from terminal (Ctrl+Z)

Summary

kill is essential for process management. Key takeaways:

Use kill PID for graceful termination
Use kill -9 PID only when necessary
Use pkill name to kill by process name
Use pgrep name to find PIDs first
Use kill -HUP to reload configs

Quick Reference

Basic

Signals

By Name

Find PID

Downloadable Image Preview

Basic Usage

Common Signals

Frequently Used Signals

Graceful vs Force Kill

Graceful termination (SIGTERM)

Force kill (SIGKILL)

Kill by Name: pkill and killall

pkill - pattern-based killing

killall - kill by exact name

Finding Process IDs

Practical Examples

Kill multiple processes

Kill all user processes

Reload configuration (HUP signal)

Pause and resume a process

Kill unresponsive terminal process

Kill all background jobs

Kill process tree

Safe Termination Pattern

Signals Reference

All Common Signals

Summary

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