How to Use Kill Commands in Linux

 Kill Command in Linux – Introduction

The ‘kill’ command in Linux is a command that is used to send signals to a process. The signals are used to ask a process to terminate gracefully, force a process to terminate immediately, pause or resume a process, or trigger custom actions in a process. The ‘kill’ command takes a process ID (PID) as its argument and sends a signal to the process with the specified PID. The default signal sent by the ‘kill’ command is ‘SIGTERM’, which asks the process to terminate gracefully. However, other signals can be specified with the -s option, such as ‘SIGKILL’, which forcefully terminates the process. The ‘kill’ command is a powerful tool for managing processes on a system of Linux.

You must first collect the PID of the process you wish to manage to use the ‘kill’ command. You can accomplish this in several methods, such as by using the ps command, the top command, or the pgrep command. The ‘kill’ command can be used to manage the process after you have its PID.

Basic steps for using the ‘kill’ command

STEP 01

Open a terminal window.

STEP 02

Use the appropriate command to obtain the PID of the process you want to manage. For instance, you can display a list of all processes that are now active on your system, together with their PIDs, by using the ‘ps’ command with the ‘aux’ option:

$ ps aux

Look for the process you want to manage in the output and note its PID.

STEP 03

To signal the process with the supplied PID, use the ‘kill’ command. The “kill” command by default emits the “SIGTERM” signal, instructing the process to die gracefully. For example, to terminate a process with a PID of 1234, you can use the following command:

$ kill 1234

If the process does not terminate after a certain period, you can end it abruptly by using the “SIGKILL” signal:

$ kill -9 1234

The ‘-9’ option specifies the ‘SIGKILL’ signal.

STEP 04

Check if the process has been terminated using the appropriate command. For instance, you can check to verify if the process is still active by using the ‘ps’ command once more:

$ ps aux | grep <process_name>

If the process is no longer running, you will not see any output.

 

These are the basic steps for using the ‘kill’ command to manage processes on a Linux system. However, some many other options and signals can be used with the ‘kill’ command, as demonstrated in the examples above. It is important to use the ‘kill’ command with caution, as it can cause unintended consequences if used improperly.

Using ‘Kill’ Command Examples

1. Terminate a process

$ kill PID

This command terminates a process with the specified process ID (PID). The default signal sent is SIGTERM, which asks the process to gracefully terminate.

2. Forcefully terminate a process

$ kill -9 PID

This command forcefully terminates a process with the specified PID by sending a SIGKILL signal, which immediately terminates the process.

3. Send a signal to a process

$ kill -SIGNAL PID

This command sends the specified signal to the process with the specified PID. Replace SIGNAL with the ‘signal’ you want to send, such as ‘HUP’, ‘INT’, or ‘USR1’.

4. Signal a process with a SIGINT signal.

$ kill -SIGINT PID

This command causes the process with the provided PID to receive a SIGINT signal, interrupting the process.

5. Send a SIGTERM signal to a process

$ kill -SIGTERM PID

This command asks the process with the provided PID to gracefully terminate by sending it a SIGTERM signal.

6. Send a SIGKILL signal to all processes with a given name

$ pkill -9 process_name

This command terminates all processes with the provided name by sending a SIGKILL signal to them.

7. Signal a process group using a SIGHUP signal.

$ kill -SIGHUP -PGID

Due to the fact that it sends a SIGHUP signal to all processes in the process group with the specified PGID, this command can be useful for reloading configuration files.

8. Give a process a SIGUSR1 signal.

$ kill -SIGUSR1 PID

This command sends the process with the specified PID a SIGUSR1 signal, which can be used to start a custom action.

9. Terminate all processes with a given name

$ pkill process_name

This command terminates all processes with the specified name.

10. Send a SIGINT signal to all processes with a given name

$ pkill -SIGINT process_name

This command causes all processes with the provided name to receive a SIGINT signal, interrupting them.

11. Send a SIGTERM signal to all processes with a given name

$ pkill -SIGTERM process_name

This command requests that all processes with the provided name gracefully terminate by sending them the SIGTERM signal.

12. Alert a process group using a signal

$ kill -SIGNAL -PGID

Using the supplied PGID, this command transmits the specified signal to every process in the process group.

13. Send a SIGUSR1 signal to all processes with a given name

$ pkill -SIGUSR1 process_name

All processes with the supplied name will receive a SIGUSR1 signal from this command, which can be used to initiate custom actions in the processes.

14. Terminate a process and all of its child processes

$ kill — -PGID

This command terminates the process group with the specified PGID, which includes the specified process and all of its child processes.

15. Send a SIGSTOP signal to a process:

This command suspends the process by sending a SIGSTOP signal to the PID that is supplied. The process can later be resumed using the kill -SIGCONT command.

$ kill -SIGSTOP PID

This can be useful for temporarily pausing a process to free up system resources or to debug it.

16. Send a SIGCONT signal to a process:

This command sends a SIGCONT signal to a process with the specified PID, which resumes a process that was previously stopped using the SIGSTOP signal.

$ kill -SIGCONT PID

17. Terminate all processes with a given name:

This command terminates all processes with the specified name.

$ pkill process_name

18. Send a SIGINT signal to all processes with a given name

This command causes all processes with the provided name to receive a SIGINT signal, interrupting them.

$ pkill -SIGINT process_name

19. Send a SIGTERM signal to all processes with a given name

This command sends a SIGTERM signal to all processes with the specified name, which asks them to gracefully terminate.

$ pkill -SIGTERM process_name

20. Send a SIGUSR1 signal to all processes with a given name:

All processes with the supplied name will receive a SIGUSR1 signal from this command, which can be used to initiate custom actions in the processes.

$ pkill -SIGUSR1 process_name

 

These examples demonstrate the versatility of the kill command, which can be used to gracefully terminate or forcefully terminate processes, send signals to individual processes or entire process groups, pause and resume processes and more.

 

Final Thoughts

The kill command causes processes to stop by signaling them to do so. It is typically a built-in shell command, which means that a user’s shell is used to execute the command as opposed to an external executable application. All PID arguments receive a signal when the kill command is used in its first form. TERM signal is the default signal for the kill command (terminate an active process). When a specific SIGNAL (name or number) is supplied, the process behaves in a predetermined manner upon receiving the signal.

You can learn about linux more deeply by clicking the link below

https://linuxiron.com/what-is-linux-a-whole-introduction/

Learn about the other linux commands by clicking the links below

https://linuxiron.com/echo-command-in-linux/

https://linuxiron.com/how-to-use-nice-renice-commands-in-linux/