How to Kill Process on Linux Server by their Port Number

 

Identifying and terminating a process running on a specific port is a common task for system administrators and anyone working with Linux systems. This process can be crucial for troubleshooting issues, freeing up ports for other applications, or managing resources effectively. While the operating system manages some listening ports, others are initiated and controlled manually. This article provides a comprehensive guide on identifying and terminating processes running on specific ports using various command-line tools in Linux.

Understanding the Need to Terminate Processes

Imagine you have an Apache server running on your Linux system, utilizing ports 80 (HTTP) and 443 (HTTPS) for web traffic. If you want to launch another web server, such as Nginx, that also uses these common ports, you need to stop the Apache server to free up the ports. This is where the ability to identify and terminate processes becomes essential.

Popular Command-Line Tools for Identifying and Terminating Processes

The Linux command line offers several powerful tools to address this task. Here's a breakdown of the most commonly used methods:

1. Killport: A Streamlined Approach

Killport is a simple and effective CLI tool designed specifically for terminating processes associated with specific ports. It simplifies the process, eliminating the need to know the service name or process ID. You only need to specify the port number.

To use Killport, you'll first need to install it on your system. Instructions for installing Killport can be found in its documentation. Once installed, you can use the following command to stop a process running on port 80 (assuming you have an Apache server running on that port):

      sudo killport 80
    

This command will terminate the process listening on port 80.

2. Fuser: Versatile for Identifying and Terminating Processes

Fuser is a versatile tool used to identify processes that are utilizing specific files, file systems, or network sockets. It's particularly helpful for identifying processes running on specific ports, but it can also be used for troubleshooting file locking, process management, and system resource issues.

Fuser is often pre-installed on popular Linux distributions like Ubuntu, Fedora, and Manjaro. If it's not available on your system, you can install it by installing the "psmisc" package, which includes Fuser and other command-line utilities.

Here's how to install "psmisc" on various Linux distributions:

• Debian, Ubuntu, Kali Linux, Linux Mint, Zorin OS, Pop!_OS:

        sudo apt install psmisc
      

  
  

• Red Hat, Fedora, CentOS, Rocky Linux, AlmaLinux:

        sudo dnf install psmisc
      

  
  

• Arch Linux, Manjaro, BlackArch, Garuda:

        sudo pacman -S psmisc
      

  
  

• OpenSUSE:

        sudo zypper install psmisc
      

  
  

To identify the process running on a specific port, use the following command, specifying the port number and the protocol (TCP or UDP):

      sudo fuser 80/tcp
    

This will display the process ID of the process handling the specified port. To terminate the process directly, use the -k option:

      sudo fuser -k 80/tcp
    

Keep in mind that Fuser may introduce a 60-second delay before the process completely shuts down as a security measure to prevent data corruption. If you need to immediately stop the process, you can use the sudo kill -9 <PID> command, replacing <PID> with the actual process ID.

3. Lsof: Powerful for Identifying Process Resources

Lsof (List Open Files) is another powerful tool that provides information about open files, directories, network sockets, and other system resources used by processes on your system. It is generally pre-installed on most Linux distributions.

To identify the process name and ID associated with a specific port, use the following command:

      sudo lsof -i :80
    

This will display output with multiple columns, but you'll primarily focus on the "COMMAND" and "PID" columns. Once you have the process ID, use the kill command to terminate the process:

      sudo kill -9 <PID>
    

You can use -9 for a forceful termination, -1 to hang up the process, or -15 (the default) for a gentler termination.

4. Netstat and Ss: Network Status Tools

Netstat and Ss are valuable tools for system administrators to quickly identify processes associated with specific ports. While Netstat is considered deprecated, it is still available on some systems and requires installation of the "net-tools" package. Ss is generally available on most systems as a more modern and improved alternative to Netstat.

Both tools utilize similar command syntax. The -tnlp option is commonly used to identify the listening port's process name and process ID.

Here's how to use netstat and ss to find the process name and ID for port 80:

sudo netstat -tnlp | grep -i :80
sudo ss -tnlp | grep -i :80
    

You can also use the service name instead of the port number in the grep command to identify the process ID and listening port:

sudo netstat -tnlp | grep -i apache
sudo ss -tnlp | grep -i apache
    

To kill the process, use the kill command with the process ID:

      sudo kill -9 <PID>
    

Important Considerations

When using these tools to terminate processes, remember that forcefully terminating a process can lead to data corruption or loss if the service is actively being used. It's important to understand the implications of terminating a process and to use caution to avoid unintended consequences.

Conclusion

Identifying and terminating processes running on specific ports is a fundamental task for system administrators and Linux users. This guide provides a detailed overview of the most common command-line tools used for this purpose, offering a comprehensive approach to managing processes and ensuring smooth operation of your Linux system.