Linux: What is Using Port [Port Number]? Find Out with This Command!
In the world of Linux, ports play a crucial role in establishing network connections. Each port is assigned a unique number, and different processes on a system can use these ports to communicate with other devices or services. However, there may be instances where you need to find out which process is using a specific port. This could be due to troubleshooting network issues, identifying potential security risks, or simply gaining a better understanding of your system’s network activity.
In this article, we will explore various methods to find out what process is using a specific port on a Linux system. We will cover command-line tools such as netstat, lsof, ss, fuser, and sockstat, each offering its own approach to retrieving this information. By the end of this article, you will have a comprehensive understanding of how to identify the process associated with a particular port.
Introduction
When a process on a Linux system wants to communicate with another device or service over a network, it needs to use a specific port. Ports are numbered from 0 to 65535, with well-known ports ranging from 0 to 1023. These well-known ports are reserved for specific services such as HTTP (port 80) or SSH (port 22).
However, there may be instances where you encounter issues with a specific port or want to investigate which process is using it. This could be due to network connectivity problems, security concerns, or simply out of curiosity. Fortunately, Linux provides several command-line tools that allow you to find out what process is using a specific port.
Why do you need to find out what process is using a specific port?
There are several reasons why you might need to find out what process is using a specific port on your Linux system:
- Troubleshooting network issues: If you’re experiencing connectivity problems with a particular port, identifying the process using it can help you pinpoint the cause of the issue.
- Identifying potential security risks: By knowing which process is using a specific port, you can ensure that only authorized services are running and detect any suspicious activity.
- Optimizing resource allocation: If you’re running multiple services on your system, identifying the processes associated with specific ports can help you allocate resources more efficiently.
- Understanding network activity: By knowing which processes are using which ports, you can gain a better understanding of your system’s network activity and how different services interact with each other.
Methods to find out what process is using a specific port
There are several methods you can use to find out what process is using a specific port on your Linux system. Let’s explore each method in detail:
Method 1: Using netstat and grep
The netstat command is a versatile tool for monitoring network connections on a Linux system. By combining it with the grep command, you can filter the output to display only the information related to a specific port.
To find out what process is using a specific port using netstat and grep, follow these steps:
- Open a terminal on your Linux system.
- Run the following command, replacing <port> with the port number you want to investigate:
netstat -tuln | grep <port>
The output will display the process ID (PID) and the corresponding process name or service associated with the specified port.
Method 2: Using lsof
The lsof command (short for “list open files”) provides detailed information about files and processes on a Linux system. It can also be used to find out what process is using a specific port.
To find out what process is using a specific port using lsof, follow these steps:
- Open a terminal on your Linux system.
- Run the following command, replacing <port> with the port number you want to investigate:
lsof -i :<port>
The output will display the process ID (PID), the user running the process, the process name or service, and other relevant information associated with the specified port.
Method 3: Using ss and grep
The ss command is another powerful tool for displaying detailed information about network connections on a Linux system. Similar to netstat, you can combine ss with grep to filter the output and find out what process is using a specific port.
To find out what process is using a specific port using ss and grep, follow these steps:
- Open a terminal on your Linux system.
- Run the following command, replacing <port> with the port number you want to investigate:
ss -tuln | grep <port>
The output will display the process ID (PID) and the corresponding process name or service associated with the specified port.
Method 4: Using fuser
The fuser command is specifically designed to identify processes using specific files or sockets on a Linux system. It can also be used to find out what process is using a specific port.
To find out what process is using a specific port using fuser, follow these steps:
- Open a terminal on your Linux system.
- Run the following command, replacing <port> with the port number you want to investigate:
fuser <port>/tcp
The output will display the process ID (PID) and the corresponding process name or service associated with the specified port.
Method 5: Using sockstat and grep
The sockstat command is a FreeBSD utility that can also be used on Linux systems to display information about open sockets. By combining sockstat with grep, you can filter the output and find out what process is using a specific port.
To find out what process is using a specific port using sockstat and grep, follow these steps:
- Open a terminal on your Linux system.
- Run the following command, replacing <port> with the port number you want to investigate:
sockstat -l | grep <port>
The output will display the process ID (PID) and the corresponding process name or service associated with the specified port.
Method 6: Using lsof, netstat, and grep
In some cases, combining multiple commands can provide more comprehensive results. By using lsof, netstat, and grep together, you can find out what process is using a specific port with additional details.
To find out what process is using a specific port using lsof, netstat, and grep, follow these steps:
- Open a terminal on your Linux system.
- Run the following command, replacing <port> with the port number you want to investigate:
sudo lsof -i -P -n | grep LISTEN | grep <port>
The output will display the process ID (PID), the user running the process, the process name or service, and other relevant information associated with the specified port.
Method 7: Using ss, netstat, and grep
Similar to the previous method, combining ss, netstat, and grep can provide more comprehensive results when finding out what process is using a specific port.
To find out what process is using a specific port using ss, netstat, and grep, follow these steps:
- Open a terminal on your Linux system.
- Run the following command, replacing <port> with the port number you want to investigate:
sudo ss -tulpn | grep <port>
The output will display the process ID (PID), the user running the process, the process name or service, and other relevant information associated with the specified port.
Method 8: Using fuser and redirecting error output
By redirecting the error output of the fuser command, you can suppress any error messages and only display the process information associated with the specified port.
To find out what process is using a specific port using fuser and redirecting error output, follow these steps:
- Open a terminal on your Linux system.
- Run the following command, replacing <port> with the port number you want to investigate:
fuser <port>/tcp 2>/dev/null
The output will display the process ID (PID) and the corresponding process name or service associated with the specified port.
Method 9: Using sockstat and awk
By combining sockstat with awk, you can filter the output and display only the process information associated with the specified port.
To find out what process is using a specific port using sockstat and awk, follow these steps:
- Open a terminal on your Linux system.
- Run the following command, replacing <port> with the port number you want to investigate:
sockstat -l | awk -v port=<port> '$0 ~ port'
The output will display the process ID (PID) and the corresponding process name or service associated with the specified port.
Conclusion
Identifying the process using a specific port on a Linux system is essential for troubleshooting network issues, ensuring security, optimizing resource allocation, and understanding network activity. In this article, we explored nine different methods to find out what process is using a specific port, using command-line tools such as netstat, lsof, ss, fuser, and sockstat.
By following the step-by-step instructions for each method, you can easily retrieve the process information associated with a particular port. Whether you prefer using netstat and grep, lsof, ss and grep, fuser, sockstat and grep, or a combination of these tools, you now have a comprehensive set of techniques to investigate port usage on your Linux system.
FAQs
1. Can I find out what process is using a specific port on remote Linux systems?
Yes, you can find out what process is using a specific port on remote Linux systems by using SSH to connect to the remote system and running the appropriate command. Make sure you have the necessary permissions and access to the remote system.
2. What should I do if I find an unauthorized process using a specific port?
If you find an unauthorized process using a specific port, it could indicate a security breach or a misconfiguration. In such cases, it is recommended to investigate further, terminate the unauthorized process if necessary, and take appropriate measures to secure your system.
3. Are there graphical tools available to find out what process is using a specific port?
Yes, there are graphical tools available for finding out what process is using a specific port on Linux systems. Some popular graphical tools include System Monitor, NetHogs, and Wireshark. These tools provide a user-friendly interface to monitor network activity and identify processes associated with specific ports.
