kill

Overview

The kill command sends signals to processes. It’s primarily used to terminate processes, but can send any specified signal to a process.

Syntax

kill [options] pid...

Common Options

Option	Description
-l	List signals
-s signal	Specify signal
-n signum	Signal number
-v	Verbose mode
-w	Wait for death
-0	Check existence
-p	Print PID
-q	Quiet mode
-a	All processes
-u user	User processes

Common Signals

Signal	Number	Description
SIGHUP	1	Hangup
SIGINT	2	Interrupt
SIGQUIT	3	Quit
SIGKILL	9	Kill
SIGTERM	15	Terminate
SIGSTOP	19	Stop
SIGCONT	18	Continue
SIGUSR1	10	User defined 1
SIGUSR2	12	User defined 2
SIGTSTP	20	Terminal stop

Key Use Cases

1. Process termination
2. Process control
3. Application restart
4. Debugging
5. System management

Examples with Explanations

Example 1: Basic Kill

kill 1234

Send SIGTERM

Example 2: Force Kill

kill -9 1234

Send SIGKILL

Example 3: List Signals

kill -l

Show available signals

Common Usage Patterns

1. Graceful stop:

   kill -15 PID

2. Force stop:

   kill -KILL PID

3. Check process:

   kill -0 PID

Signal Handling

1. Default action
2. Ignore signal
3. Catch signal
4. Block signal
5. Process groups

Related Commands

• pkill - Process kill
• killall - Kill by name
• pgrep - Process grep
• ps - Process status
• top - Process viewer

Additional Resources

• Kill Manual
• Signal Guide
• System Administration

Best Practices

1. Use SIGTERM first
2. Wait for exit
3. Check status
4. Document actions
5. Verify results

Security Considerations

1. Process ownership
2. Signal permissions
3. System impact
4. Zombie processes
5. Resource cleanup

Troubleshooting

1. Process won’t die
2. Permission denied
3. Invalid PID
4. Zombie processes
5. Signal handling

Process States

1. Running
2. Sleeping
3. Stopped
4. Zombie
5. Dead