Linux check who use port

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Often we need to find out a process or a service running on some port. This is because we have to start a new instance of the same or different service on that port but we cannot until the current process is terminated.
Thus, it is required to find out the PID of a process using its port so that the process can be terminated.
There are many different ways in which a process can be checked using its port and this article will discuss them in detail with example.

Method 1 : Using lsof command
lsof stands for List of open files and can be used to retrieve details of open files on linux. Since a process running on linux is also a file, this command can be used to get the information about a process.
lsof has an -i flag which lists out all the files that are opened by network connections or listening on different ports and returns the name of process, its PID, user who started the process and port number on which the process is running along with other details.
This flag should be followed by a colon and the port number for which you want the process details.
Thus, for finding a process running on port 9090, use the below command

Notice that there should be no space between -i , : and 9090.
It displays the below output

COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
app 26549 root 4u IPv6 2427316 0t0 TCP *:9090 (LISTEN)

If lsof is not already installed on your system, then install it using apt or yum as shown below

# use apt
sudo apt install lsof

# or use yum
sudo yum install lsof

Method 2 : Using netstat command
netstat stands for Network Statistics and is a utility for displaying information about network and related details over TCP/IP protocol. This utility is available in Windows, Linux and Mac operating systems.
In order to view a process running on a particular port, use this command with -l and -p flags along with grep command to filter out unwanted port details.
Here -l flag is used to list out all Listening ports and -p is required for displaying the PID of the process. If you do not want the PID of the processes then omit the -p flag.
Thus, to list out the process details running on port 9090, use the following command

netstat -lp | grep 9090

which prints the below result

where 26549 is the PID of the process running on port 9090.
If you omit the -p flag, the modified output will be

Note that now there is no PID.
If netstat is not already installed on your system, then install it using apt or yum as shown below

# use apt
sudo apt install net-tools

# or use yum
sudo apt install net-tools

Method 3 : Using fuser command
fuser command is used to display details of a process that is using a particular file, folder or socket. As stated earlier, a process in linux is also a file and if you know anything about that process such as its port number(or socket), then fuser can be used to display its details.
To display the details of a process running on port 9090, use the below command.

sudo fuser -v 9090/tcp

where tcp is the protocol on which the process is running and -v flag stands for verbose and it is used to display a detailed output.
Thus, above command will output

If used without -v flag, fuser will only display the PID of the process as shown below

This command also has a -k flag which can be directly used to kill the process that is returned by the command output. Thus, you do not need to explicitly use kill for terminating a process as with other methods stated above.
If fuser is not already installed on your system, then install it using apt or yum as shown below

# use apt
sudo apt install psmisc

# or use yum
sudo yum install psmisc

Method 4 : Using ss command
ss command can also be used to display details about a process. To find out details of a process running on a port, pipe its pipe its output to grep command to show the results of a specific port.
Below command will display the processes listening on a specific port.

sudo ss -ltp | grep 9090

where -l will display listening processes, -t will show only tcp processes and -p will also display the PID of the processes. Output of above command will be

Remember that if you are logged in with root user, then you do not need to add sudo before the command.
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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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