Linux find which process port

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.

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).

Check Port Using netstat Command

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.

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

Find Port Using lsof Command

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:

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.

Find Port and Process ID in Linux

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

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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Linux Find Out Which Process Is Listening Upon a Port

Linux Find Out Which Process Is Listening Upon a Port

You can the following programs to find out about port numbers and its associated process:

1. netstat command or ss command – a command-line tool that displays network connections, routing tables, and a number of network interface statistics.
2. fuser command – a command line tool to identify processes using files or sockets.
3. lsof command – a command line tool to list open files under Linux / UNIX to report a list of all open files and the processes that opened them.
4. /proc/$pid/ file system – Under Linux /proc includes a directory for each running process (including kernel processes) at /proc/PID, containing information about that process, notably including the processes name that opened port.

You must run above command(s) as the root user.

Linux netstat command find out which process is listing upon a port

Type the following command:
# netstat -tulpn
Sample outputs:

TCP port 3306 was opened by mysqld process having PID # 1138. You can verify this using /proc, enter:
# ls -l /proc/1138/exe
Sample outputs:

You can use grep command or egrep command to filter out information:
# netstat -tulpn | grep :80
Sample outputs:

A note about ss command

Some Linux distro considered the nestat command as deprecated and therefore should be phased out in favor of more modern replacements such as ss command. The syntax is:
$ sudo ss -tulpn
$ sudo ss -tulpn | grep :3306

Click to enlarge image

Video demo

fuser command

Find out the processes PID that opened tcp port 7000, enter:
# fuser 7000/tcp
Sample outputs:

Finally, find out process name associated with PID # 3813, enter:
# ls -l /proc/3813/exe
Sample outputs:

/usr/bin/transmission is a bittorrent client, enter:
# man transmission
OR
# whatis transmission
Sample outputs:

Find Out Current Working Directory Of a Process

To find out current working directory of a process called bittorrent or pid 3813, enter:
# ls -l /proc/3813/cwd
Sample outputs:

OR use pwdx command, enter:
# pwdx 3813
Sample outputs:

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Find Out Owner Of a Process on Linux

Use the following command to find out the owner of a process PID called 3813:
# ps aux | grep 3813
OR
# ps aux | grep ‘[3]813’
Sample outputs:

OR try the following ps command:
# ps -eo pid,user,group,args,etime,lstart | grep ‘[3]813’
Sample outputs:

Another option is /proc/$PID/environ, enter:
# cat /proc/3813/environ
OR
# grep —color -w -a USER /proc/3813/environ
Sample outputs (note –colour option):

Fig.01: grep output

lsof Command Example

Type the command as follows:

Now, you get more information about pid # 1607 or 1616 and so on:
# ps aux | grep ‘[1]616’
Sample outputs:
www-data 1616 0.0 0.0 35816 3880 ? S 10:20 0:00 /usr/sbin/apache2 -k start
I recommend the following command to grab info about pid # 1616:
# ps -eo pid,user,group,args,etime,lstart | grep ‘[1]616’
Sample outputs:

• 1616 : PID
• www-date : User name (owner – EUID)
• www-date : Group name (group – EGID)
• /usr/sbin/apache2 -k start : The command name and its args
• 03:16:22 : Elapsed time since the process was started, in the form [[dd-]hh:]mm:ss.
• Fri Oct 29 10:20:17 2010 : Time the command started.

Help: I Discover an Open Port Which I Don’t Recognize At All

The file /etc/services is used to map port numbers and protocols to service names. Try matching port numbers:
$ grep port /etc/services
$ grep 443 /etc/services
Sample outputs:

Check For rootkit

I strongly recommend that you find out which processes are really running, especially servers connected to the high speed Internet access. You can look for rootkit which is a program designed to take fundamental control (in Linux / UNIX terms “root” access, in Windows terms “Administrator” access) of a computer system, without authorization by the system’s owners and legitimate managers. See how to detecting / checking rootkits under Linux.

Keep an Eye On Your Bandwidth Graphs

Usually, rooted servers are used to send a large number of spam or malware or DoS style attacks on other computers.

Conlcusion

You learned various Linux commands to find information about running process and their ports. See the following man pages for more information:
$ man ps
$ man grep
$ man lsof
$ man netstat
$ man fuser

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Linux: Find Out Which Port Number a Process is Listening on

As Linux users, we sometimes need to know which port number a particular process is listening upon. All ports are associated with a process ID or service in an OS. So how do we find that port? This article presents three different methods for you to find which port number a process is listening on.

We have run the commands and procedures described in this article on an Ubuntu 18.04 LTS system.

Method 1: Using the netstat command

Netstat or the network statistics utility is used to view information related to the network connections. This includes information about interface statistics, routing tables and much more. This utility is available on most Linux systems so let us make use of it to view information about which ports certain processes are using on the system.

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

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.

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

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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 the process ID 975 corresponds to the program names 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.

Karim Buzdar

About the Author: Karim Buzdar holds a degree in telecommunication engineering and holds several sysadmin certifications. As an IT engineer and technical author, he writes for various web sites. You can reach Karim on LinkedIn

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How to check if port is in use on Linux or Unix

H ow do I determine if a port is in use under Linux or Unix-like system? How can I verify which ports are listening on Linux server? How do I check if port is in use on Linux operating system using the CLI?

It is important you verify which ports are listening on the server’s network interfaces. You need to pay attention to open ports to detect an intrusion. Apart from an intrusion, for troubleshooting purposes, it may be necessary to check if a port is already in use by a different application on your servers. For example, you may install Apache and Nginx server on the same system. So it is necessary to know if Apache or Nginx is using TCP port # 80/443. This quick tutorial provides steps to use the netstat, nmap and lsof command to check the ports in use and view the application that is utilizing the port.

Tutorial details
Difficulty level	Easy
Root privileges	Yes
Requirements	lsof, ss, and netstat on Linux
Est. reading time	3 minutes

How to check if port is in use in

To check the listening ports and applications on Linux:

1. Open a terminal application i.e. shell prompt.
2. Run any one of the following command on Linux to see open ports:
   sudo lsof -i -P -n | grep LISTEN
   sudo netstat -tulpn | grep LISTEN
   sudo ss -tulpn | grep LISTEN
   sudo lsof -i:22 ## see a specific port such as 22 ##
   sudo nmap -sTU -O IP-address-Here
3. For the latest version of Linux use the ss command. For example, ss -tulw

Let us see commands and its output in details.

Option #1: lsof command

The syntax is:
$ sudo lsof -i -P -n
$ sudo lsof -i -P -n | grep LISTEN
$ doas lsof -i -P -n | grep LISTEN ### [OpenBSD] ###
Sample outputs:

Fig.01: Check the listening ports and applications with lsof command

Option #2: netstat command

You can check the listening ports and applications with netstat as follows.

Linux netstat syntax

Run netstat command along with grep command to filter out port in LISTEN state:
$ netstat -tulpn | grep LISTEN
The netstat command deprecated for some time on Linux. Therefore, you need to use the ss command as follows:
sudo ss -tulw
sudo ss -tulwn
sudo ss -tulwn | grep LISTEN

Where, ss command options are as follows:

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• -t : Show only TCP sockets on Linux
• -u : Display only UDP sockets on Linux
• -l : Show listening sockets. For example, TCP port 22 is opened by SSHD server.
• -p : List process name that opened sockets
• -n : Don’t resolve service names i.e. don’t use DNS

FreeBSD/MacOS X netstat syntax

$ netstat -anp tcp | grep LISTEN
$ netstat -anp udp | grep LISTEN

OpenBSD netstat syntax

$ netstat -na -f inet | grep LISTEN
$ netstat -nat | grep LISTEN

Option #3: nmap command

The syntax is:
$ sudo nmap -sT -O localhost
$ sudo nmap -sU -O 192.168.2.13 ##[ list open UDP ports ]##
$ sudo nmap -sT -O 192.168.2.13 ##[ list open TCP ports ]##
Sample outputs:

Fig.02: Determines which ports are listening for TCP connections using nmap

A note about Windows users

You can check port usage from Windows operating system using following command:
netstat -bano | more
netstat -bano | grep LISTENING
netstat -bano | findstr /R /C:»[LISTEING]»

Conclusion

This page explained command to determining if a port is in use on Linux or Unix-like server. For more information see the nmap command and lsof command page online here

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