Managing Processes (kill)

The kill command sends signals to processes, allowing you to stop, pause, or control running programs.

Basic Usage

kill PID
kill -9 PID

Understanding Signals

Signals are messages sent to processes:

Signal	Number	Name	Effect
SIGTERM	15	Terminate	Graceful shutdown
SIGKILL	9	Kill	Forced shutdown
SIGHUP	1	Hangup	Restart/reload
SIGSTOP	19	Stop	Pause process
SIGCONT	18	Continue	Resume process

Common kill Commands

kill PID              # Graceful (SIGTERM)
kill -9 PID           # Force kill (SIGKILL)
kill -HUP PID         # Restart/reload
kill -STOP PID        # Pause
kill -CONT PID        # Resume

Finding the PID

Before killing, find the process ID:

ps aux | grep process_name
pgrep process_name
pidof program

Exercise: Find and Signal Process

View a process and understand how to send signals:

killall - Kill by Name

Kill processes by name instead of PID:

killall firefox
killall -9 chrome
killall -u username     # All processes by user

pkill - Pattern-Based Kill

More flexible than killall:

pkill firefox           # Match process name
pkill -f "python app"   # Match full command
pkill -u www-data       # By user

Graceful vs Force Kill

SIGTERM (default, signal 15)

• Allows cleanup
• Process can save data
• May be ignored

kill PID
kill -15 PID
kill -TERM PID

SIGKILL (signal 9)

• Cannot be ignored
• No cleanup opportunity
• Last resort

kill -9 PID
kill -KILL PID

Common Scenarios

Stop Unresponsive Program

# Try graceful first
kill PID

# If still running, force kill
kill -9 PID

Restart Service

kill -HUP $(pidof nginx)
# nginx reloads config

Kill All User Processes

pkill -u username

Kill Process on Port

kill $(lsof -t -i:8080)

Safety Tips

1. Check before killing: Verify PID is correct
2. Try graceful first: Use SIGTERM before SIGKILL
3. Don't kill PID 1: That's init/systemd (system will crash)
4. Be careful with killall: Make sure name is specific

Alternatives

On Modern Systems

systemctl stop service     # Stop a service
systemctl restart service  # Restart a service

GUI Method

Use your desktop's system monitor or task manager.

Related Commands

Command	Purpose
kill	Send signal to PID
killall	Kill by exact name
pkill	Kill by pattern
xkill	Kill by clicking window
htop	Interactive process manager

Key Takeaways

• kill PID sends SIGTERM (graceful stop)
• kill -9 PID forces immediate termination
• Find PID first with ps aux | grep or pgrep
• Always try graceful termination first
• Use killall or pkill to kill by name