Kill Process in Linux: The Ultimate 2026 Guide

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kill process in linux

Kill Process in Linux Eventually, all types of Linux users ā€” from the desktop fanatics to the enterprise sysadmins ā€” are going to come across an application that has become unresponsive or a rogue task that is impacting performance on your machine.

When your computer is running very slowly, one of the fastest methods of regaining control is learning how to kill process in linux.

Kill process in linux is not only a method of stopping applications, but it is really a way of managing system resources, preserving data integrity and understanding how the linux kernel communicates with running applications.

This article will explore every method available to the average user for kill a process in linux; from basic terminal commands to advanced signal management to graphical user interfaces. When you finish reading this article, you will know how to safely handle any “unresponsive” situation.

Table of Contents

1. The Fundamentals: What is a Linux Process?

In Linux, a “process” is an instance of a program that is currently running. Each process has its own unique ID number assigned by the kernel called the Process ID (PID).

All processes have a lifecycle. A parent process starts the lifecycle of a process and can generate child, or offspring, processes that will eventually end the same way the parent did when it’s finished running.

When you try to kill a process in Linux, you are requesting the kernel to terminate its lifecycle and retrieve the resources it has been consuming (memory, CPU cycles).

2. Identifying the Target: ps, pgrep, and pidof

In order to kill a process in Linux you must know the PID of the process that you want to kill or be able to shoot in the dark at an unknown PID. Therefore, killing with a random PID will create instability in the system.

Using the ps command is the traditional way to view processes, but if you wish to see detailed information on each running process on the operating system, you can do this using the following command:

ps aux | grep [process_name]

This command will return detailed information about the running process including who owns the process, how much memory is currently in use by the process and the PID of the process being requested.

An even faster way to find a process is to use the pgrep command, which can be executed once you know the name of a running application. The pgrep command searches through the process table and only returns the PID:

pgrep firefox

3. kill a process in linux: Syntax and Basic Usage

Although Named after the word ā€œkillā€, kill sends a signal to the specified PID to perform some action on it instead of simply killing it. The syntax to kill/terminate in Linux is:

kill [signal] [PID]

For example, just issuing the command kill 1024 with no signal specified will result in the system sending SIGTERM(15) as the default signal.

This is a ā€œcleanā€ termination signal meaning the application being terminated will be given the opportunity to make sure it saves its current state, deletes any temporary files created by the application and closes any TCP/IP network connections properly before terminating itself.

4. Understanding Linux Signals (15 vs. 9)

To successfully execute a command that kill process in Linux OS it’s essential to know about the various types of termination signals. There are more than sixty different signals available, but here are the most significant ones:

  • SIGTERM (15): The polite way of asking a process to terminate. This should always be your first attempt to kill a process in linux.
  • SIGKILL (9): The ‘forceful kill’ of a process. Use only when absolutely necessary i.e., when a process is completely unresponsive.
  • SIGINT (2): The keyboard interrupt. Usually caused when you press Ctrl+C to stop a executing program.
  • SIGSTOP (19): A signal which will pause a executing program without terminating it.

Note: Understanding the difference between these signals is key to maintaining a stable system without data loss.

5. Terminating by Name: killall and pkill

If you want to know the process id (PID) for a program, such as a web browser, and there are twenty running instances of that program running, manually finding each one (PID) can be time-consuming.. To stop a process on a Linux machine by name, you would use the command “killall” or “pkill”.

For example:

killall chrome

By using the command above, the computer finds every instance of the process “chrome” and sends them SIGTERM, or terminate, to each one.

Conversely, “pkill” can be much more flexible, because it allows you to match part of a name (i.e. “python”) and filter by user id. In this case, the user id is “bob”.

pkill -u bob python

6. How to Kill Process in Linux by Port (fuser & lsof)

You might not always be able to identify which specific program is taking controlā€”what process is running on your computer; however, you at least know that the program blocking that port (80 or 8080) is often found in web development.

To locate and delete a process that is using up a port on Linux, run fuser:

sudo fuser -k 8080/tcp

-Via the -k flag, the utility will terminate any processes it can find using that port right away.

7. Interactive Management: top, htop, and btop

Terminal-based systems are the best option if you prefer a graphical user interface. For professional users, htop is often a preferred tool as you can view process information sorted by CPU usage, search for processes by name, and interactively terminate processes in Linux using the F9 key.

Note: Using interactive tools like htop provides a visual “Task Manager” experience within the terminal, making it easier to identify and manage resource-heavy applications.

8. Deep Dive: Process States

Not all processes immediately respond to the kill command. To better understand how processes will respond, take note of the “State” column in ps or top:

  • S (Interruptible Sleep): The process is waiting for a user to perform an action or issue a signal. The process may be easily killed.
  • D (Uninterruptible Sleep): This is usually waiting for Disk I/O and will often not respond to kill -9 until hardware returns an answer.
  • Z (Zombie): The process is dead but still has a PID. You cannot kill a zombie; you must kill its parent.

9. Managing Services with Systemd (systemctl)

Background tasks in modern distributions, whether powered by Ubuntu or RHEL are “Service Managers” which manage “background tasks” or services in Linux. You may try to kill a process in linux that’s managed by systemd through a kill command; however, it may restart again automatically.

In order to stop them properly, you should use:Ā 

sudo systemctl stop [service_name]

10. Troubleshooting: What to do when kill -9 fails

Many people think that using a kill -9 command will always be able to kill a process. However, if a process is hanging in a D state (indicated by the system waiting for an I/O to complete) there are cases where the kernel cannot kill it.

In these situations your only options are to either wait for the I/O to time-out or reboot your system.

11. Expert Best Practices for Process Termination

  • Follow the Escalation Path: Use kill -15 to start with, and wait 5-10 seconds for that to take effect. If that fails, use kill -9.
  • Check Permissions: Only you can kill a process in linux if you are the owner of the process. If you want to kill a system process, you will need to use sudo.
  • Use xkill for GUIs: If you are on a desktop, xkill is the easiest way to kill a frozen program. If you run xkill, you can click on the frozen window to kill it.

12. 20 Frequently Asked Questions (FAQ)

  1. What is the command to kill process in linux? The primary command is kill [PID].
  2. What does kill -9 do? It sends the SIGKILL signal, which forces a process to terminate immediately.
  3. How do I kill all processes of a user? Use pkill -u [username].
  4. Can I kill multiple PIDs at once? Yes, kill PID1 PID2 PID3.
  5. How do I find the PID of the last run command? Use echo $!.
  6. What is a zombie process? A process that has finished but stays in the process table.
  7. How to kill a zombie process? Kill its parent process using kill -9 [PPID].
  8. What is SIGTERM? Signal 15, the default termination signal for graceful shutdowns.
  9. How to kill process in linux by name? Use killall [name] or pkill [name].
  10. What happens if I kill the init process (PID 1)? The system will crash or reboot immediately.
  11. How to stop a process without killing it? Use kill -STOP [PID].
  12. How do I resume a stopped process? Use kill -CONT [PID].
  13. What is SIGHUP? Signal 1, used to tell a process to reload its configuration.
  14. How to kill a process on port 80? Use sudo fuser -k 80/tcp.
  15. Can a non-root user kill a root process? No, you must use sudo.
  16. Why is kill -9 dangerous? It can cause data loss or corrupt databases.
  17. How do I see a live list of processes? Use the top or htop command.
  18. What is the signal for Ctrl+C? SIGINT (Signal 2).
  19. How to find the parent of a process? Use ps -o ppid= -p [PID].
  20. Is there a way to undo a kill process in linux? No, once killed, the process must be manually restarted.

Conclusion: Learning how to kill process in linux is an indispensable skill. Whether you use the surgical precision of the kill command or the broad strokes of killall, always prioritize graceful termination (SIGTERM) to keep your data safe. Master these tools, and you will ensure your Linux system remains fast, stable, and responsive.

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