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To terminate a process in Linux, you can use the commands kill, pkill, or killall.

1. Using kill:

• Ends a process by its Process ID (PID).
• Requires knowing the PID.
• Signals:
  • SIGTERM (default, 15): Gentle termination, allows the process to close properly.
  • SIGKILL (9): Immediate and forceful termination, the process cannot ignore this signal.

# find the PID of the process
ps aux | grep <process_name>

# send SIGTERM signal (default)
kill <PID>

# send SIGKILL signal
kill -9 <PID>

2. Using pkill:

• Ends processes by name or other attributes.
• Does not require knowing the PID.
• Supports patterns.

# terminate all processes named 'nginx'
pkill nginx

# terminate all processes containing 'myapp' in their name (case-sensitive)
pkill -i myapp

# send SIGKILL to processes named 'firefox'
pkill -9 firefox

3. Using killall:

• Ends processes only by their exact name.
• Does not support complex patterns, unlike pkill.

# terminate all processes with the exact name 'apache2'
killall apache2

# send SIGKILL to processes with the exact name 'mysqld'
killall -9 mysqld

Choice of command:

Command	Method of termination	Requires PID	Pattern support
kill	By PID	Yes	No
pkill	By name/attributes	No	Yes
killall	By exact name	No	No

In most cases, it is recommended to first try to terminate the process using SIGTERM (kill <PID>, pkill <name>), giving it the chance to save data and close properly. SIGKILL (kill -9, pkill -9, killall -9) should only be used as a last resort when the process does not respond to other signals.