What does the pkill command do in Linux?

The pkill command sends a signal (by default, SIGTERM) to processes based on their name or other attributes. It is similar to killall but offers more flexible pattern matching and selection criteria.

How do I kill a process using pkill?

Use 'pkill process_name' (e.g., 'pkill firefox') to send a SIGTERM signal to all processes matching 'firefox'.

What is the difference between pkill and killall?

Both pkill and killall terminate processes by name. However, pkill uses regular expressions for pattern matching by default, offering more powerful and flexible search capabilities than killall.

pkill Command

The pkill command in Linux is a command-line utility used to send signals (like termination signals) to processes based on their name or other attributes. It is a more powerful and flexible alternative to killall and is often used in scripts for efficient process management.

Syntax

pkill [OPTION]... PATTERN

Description

pkill works by searching for processes that match the provided PATTERN (which is a regular expression by default) and then sending a specified signal to them. If no signal is specified, it sends SIGTERM (signal 15), which is a request for graceful termination. It is part of the procps-ng package, along with pgrep.

Common uses include:

Terminating processes by name or partial name.
Sending specific signals to processes (e.g., SIGHUP to reload configurations).
Killing processes owned by a particular user or group.
Targeting processes based on their parent process ID.

Common Options

Option	Description
`-SIGNAL, -s SIGNAL`	Specify the signal to send (e.g., `-9` for SIGKILL, `-HUP` for SIGHUP).
`-u, --euid <user>`	Match processes whose effective user ID is <user>.
`-G, --egid <group>`	Match processes whose effective group ID is <group>.
`-f, --full`	The pattern is matched against the full command line.
`-n, --newest`	Select the newest (most recently started) of the matching processes.
`-o, --oldest`	Select the oldest (least recently started) of the matching processes.
`-x, --exact`	Only match processes whose name is exactly PATTERN.
`-P, --parent <ppid>`	Match only children of the process with specified parent PID.

Examples

Terminate a process by name

pkill firefox

Sends a SIGTERM signal to all running processes named firefox.

Forcefully kill a process

                        pkill -9 chrome
                        
                        # Or:
                        
                        pkill -s SIGKILL chrome

Sends a SIGKILL signal (signal 9) to all chrome processes, which cannot be ignored.

Send SIGHUP to a process (e.g., for graceful reload)

pkill -HUP nginx

Sends a SIGHUP signal to all nginx processes, often used to tell a daemon to reload its configuration files.

Kill processes owned by a specific user

pkill -u guest_user

Kills all processes owned by the user guest_user.

Kill processes matching a full command line

pkill -f "java -jar my_application.jar"

Kills processes whose full command line matches the specified pattern.