Linux show processes and ports

3 Ways to Find Out Which Process Listening on a Particular Port

A port is a logical entity that represents an endpoint of communication and is associated with a given process or service in an operating system. In previous articles, we explained how to find out the list of all open ports in Linux and how to check if remote ports are reachable using the Netcat command.

In this short guide, we will show different ways of finding the process/service listening on a particular port in Linux.

1. Using netstat Command

netstat (network statistics) command is used to display information concerning network connections, routing tables, interface stats, and beyond. It is available on all Unix-like operating systems including Linux and also on Windows OS.

In case you do not have it installed by default, use the following command to install it.

$ sudo apt-get install net-tools [On Debian/Ubuntu & Mint] $ sudo dnf install net-tools [On CentOS/RHEL/Fedora and Rocky Linux/AlmaLinux] $ pacman -S netstat-nat [On Arch Linux] $ emerge sys-apps/net-tools [On Gentoo] $ sudo dnf install net-tools [On Fedora] $ sudo zypper install net-tools [On openSUSE]

Once installed, you can use it with the grep command to find the process or service listening on a particular port in Linux as follows (specify the port).

In the above command, the flags.

• l – tells netstat to only show listening sockets.
• t – tells it to display tcp connections.
• n – instructs it to show numerical addresses.
• p – enables showing of the process ID and the process name.
• grep -w – shows matching of exact string (:80).

Note: The netstat command is deprecated and replaced by the modern ss command in Linux.

2. Using lsof Command

lsof command (List Open Files) is used to list all open files on a Linux system.

To install it on your system, type the command below.

$ sudo apt-get install lsof [On Debian, Ubuntu and Mint] $ sudo yum install lsof [On RHEL/CentOS/Fedora and Rocky Linux/AlmaLinux] $ sudo emerge -a sys-apps/lsof [On Gentoo Linux] $ sudo pacman -S lsof [On Arch Linux] $ sudo zypper install lsof [On OpenSUSE]

To find the process/service listening on a particular port, type (specify the port).

3. Using fuser Command

fuser command shows the PIDs of processes using the specified files or file systems in Linux.

You can install it as follows:

$ sudo apt-get install psmisc [On Debian, Ubuntu and Mint] $ sudo yum install psmisc [On RHEL/CentOS/Fedora and Rocky Linux/AlmaLinux] $ sudo emerge -a sys-apps/psmisc [On Gentoo Linux] $ sudo pacman -S psmisc [On Arch Linux] $ sudo zypper install psmisc [On OpenSUSE]

You can find the process/service listening on a particular port by running the command below (specify the port).

Then find the process name using PID number with the ps command like so.

$ ps -p 2053 -o comm= $ ps -p 2381 -o comm=

You can also check out these useful guides about processes in Linux.

You might also like:

That’s all! Do you know of any other ways of finding the process/service listening on a particular port in Linux, let us know via the comment form below.

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Check Which Process Is Using a Port on Linux

In computer networking, a port represents a logical entry and exit point for a connection. Ports are based on software and are entirely virtual. These ports on a computer are managed by the operating system.

What Will We Talk About?

This quick tutorial demonstrates the various methods to determine which Linux process or service is currently listening on a specific port. Let’s talk about ports and their purpose.

How Are Ports Analogous to Physical Ports?

Just as physical ports help to interact with various peripheral devices connected to a computer, ports help the different services to communicate with each other. These services can be on the same computer or on different computers.

A Bit About Port of a Service

To listen for incoming connection requests, a process associates itself with a port number. Most processes are set up with a default port, and they have to use that port as per their specification. They do not automatically switch to the other port unless their configuration is explicitly modified.

A few examples of protocols and their associated default ports include the Secure Shell (SSH) protocol (port22), the Apache HTTP (port80), the MySQL database server (port3306), and so forth. You may use this information to discover which default port does a service utilizes.

The config file of these services can be edited to use some other port as well.

Checking the Ports on Linux

Let’s now see how to check what port/ports a process is using on Linux. Here, we will show you the different commands for this purpose.

1. Lsof Command

The lsof utility is helpful to obtain a list of the ports which are used by your system. Let’s consider the following example to get an information about a process (processes) using the TCP port 22:

The lsof command gives more information like the user’s name and what process IDs are linked to each process. It works with both TCP and UDP ports.

2. SS Command

The ss command is another way to find out which processes are linked to a certain port. Although lsof is the more common abbreviation, some people may find ss to be more handy.

Let’s look for the processes or services that listen on port 3306:

Let’s break down this command:

1. t: It tells the ss command to display the TCP packets.

2. u: It tells the ss command to display the UDP packets.

3. n: It is used to display the port numbers instead of their translations.

4. a: It is used to display the listening as well as non-listening sockets of all types.

5. p: It is used to display the processes that utilize a socket.

The result of the previous command shows which process is utilizing which port. You may also issue the following command:

Here, sport signifies the source port.

These two approaches may help you find the IDs of the processes that are connected to different ports.

3. Netstat Command

The netstat command shows the information about your network and can be used to fix the problems or change the way that your network is set up. It can also keep a close watch on your network connections.

This command is often used to see an information about inbound and outbound connections, routing tables, port listening, and usage stats. Although it has been rendered obsolete in recent years, netstat is still a useful tool for analyzing networks.

With the grep command, netstat can determine which process or service is using a certain port (by mentioning the port):

The options used here can be classified as follows:

1. t: It only shows the TCP connection.

2. l: It is used to display the results in a list.

3. n: It displays addresses and port numbers in numerical format.

4. p: It displays the PID and program name which are associated with each socket.

4. Fuser Command

The fuser command determines the processes that utilize the files or sockets. You can use it to list the services which run on a specific port. Let’s take the example of port 3306 and see what services are running here:

This provides us with the process numbers using this port. You can use this process number to find the corresponding process names. For example, if the process number is 15809, the command to use here is as follows:

However, certain tools are required to identify the processes that utilize a non-standard port. “LSOF” is a tool for discovering what services are available on a network and what ports they use. Consider the following example. This shows how to list the UDP and TCP listening ports:

The following is a description of the options that are used here:

1. P: It suppresses the port service name lookup.

2. n: It displays the numeric network addresses.

3. i: It lists the IP sockets.

Both the ports and the associated processes are shown in the previously-mentioned result. This way is particularly useful for processes with non-default ports.

Conclusion

In this article, we talked about four possible Linux command-line tools and provided the examples on how to use them to find out which process is listening on a certain port.

About the author

Ali Imran Nagori

Ali imran is a technical writer and Linux enthusiast who loves to write about Linux system administration and related technologies. You can connect with him on LinkedIn
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Linux: Find Out Which Port Number a Process is Listening on

As Linux users, we sometimes need to know what port number a particular process is listening on. All ports are associated with a process ID or service in an operating system. So how do we find this port? In this article, we will present three different methods that you can use to find out which port a process is listening on.

We have run the commands and procedures described in this article on an Ubuntu 22.04 LTS system.

Method 1: Using the netstat command

Netstat, the network statistics utility, is used to display information about the network connections. This includes information about interface statistics, routing tables and much more. This utility is available on most Linux systems, so we use it to find out which ports certain processes on the system are using.

To use the netstat command, you must install the net-tools utility, if it is not already installed on your system, using the following command:

$ sudo apt install net-tools

Then run the following command:

The above command gives netstat information based on the following features:

• l: display only listening sockets
• t: display tcp connection
• n: display addresses in a numerical form
• p: display process ID/ Program name

For example, in the above output of the netstat command, Apache2 program with process ID 950 is running on port number 80.

You can also filter statistics for a specific port by incorporating the grep function into your command.

$ sudo netstat -ltnp | grep -w ':80'

This command will tell you specifically which process is running on port number 80.

Method 2: Using the lsof command

The lsof or the List of Open Files utility helps in listing all the open files on your Linux system. We can use this utility to view all processes open on a specific port.

For using the lsof command, you need to install the lsof utility if it is already not installed on your system through the following command:

Let us use lsof to view the service listening on a specific port.

This command will list all processes using TCP port number 80.

Method 3: Using the fuser command

The fuser command displays which process IDs are using the named files, sockets or file systems. We can use this command in order to view process IDs running on a specific TCP port.

For using the fuser command, you need to install the psmisc utility if it is already not installed on your system through the following command:

Let us view all the process IDs running on TCP port 3306 through the following command:

You can specify any port number in this command to view its listening processes.

In the above output, you can see that process ID 975 is listening on TCP 3306.

In order to view which program this process ID corresponds to, run the following command:

The output shows that process ID 975 corresponds to the program name MySDLd. Thus process ID 975 of the program MySQLd is listening on port number 3306.

Through the three methods you have learned in this article, you can easily view which TCP port a specific process on Linux is listening upon.

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