Port command in linux

Linux find out which port is open using the command line

Linux find out which port is open using the command line

The procedure to list open ports in Linux is as follows:

1. Open the terminal application
2. Use command netstat -tulpn to open ports
3. Another option is to run ss -tulpn to open ports on modern Linux distros

Let us see all commands in details.

Linux find port open command

One can use the netstat command or ss command find out which process is listing upon a port:
$ sudo netstat -tulpn
$ sudo netstat -tulpn | more
$ sudo netstat -tulpn | grep ‘:port’
$ sudo netstat -tulpn | grep ‘:22’
OR
$ sudo ss -tulpn
$ sudo ss -tulpn | more
$ sudo ss -tulpn | grep ‘:port’
$ sudo ss -tulpn | grep ‘:22’

Click to enlarge image

How to find out and list of all open TCP/UDP ports in Linux

Other commands that you can use are as follows.

fuser command examples to find out which port is open

One can list the processes PID that opened tcp port 22, enter:
$ sudo fuser 22/tcp
Sample outputs:

Let us see process name associated with PID # 1462, execute:
$ sudo ls -l /proc/1462/exe
Outputs:

/usr/sbin/sshd has opened tcp port 22. But, what is sshd? Let us find out:
$ whatis sshd
Example outputs:

How to use lsof command to display open port on Linux

$ sudo lsof -i :portNumber
$ sudo lsof -i tcp:portNumber
$ sudo lsof -i udp:portNumber
$ sudo lsof -i :22
$ sudo lsof -i :22 | grep LISTEN

Click to enlarge file

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Conclusion

You just learned how to list open ports on a Linux based system. For more info see man pages.

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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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How to Find Out List of All Open Ports in Linux

In this article, we will briefly talk about ports in computer networking and move to how you can list all open ports in Linux.

In computer networking, and more definitely in software terms, a port is a logical entity which acts as a endpoint of communication to identify a given application or process on an Linux operating system. It is a 16-bit number (0 to 65535) which differentiates one application from another on end systems.

The two most popular Internet transport protocols, Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) and other less known protocols use port numbers for communication sessions (source and destination port numbers in conjunction with the source and destination IP addresses).

In addition, a combination of an IP address, port and protocol such as TCP/UDP is known as a socket, and every service must have a unique socket.

Below are the different categories of ports:

1. 0-1023 – the Well Known Ports, also referred to as System Ports.
2. 1024-49151 – the Registered Ports, also known as User Ports.
3. 49152-65535 – the Dynamic Ports, also referred to as the Private Ports.

You can view a list of different applications and port/protocol combination in /etc/services file in Linux using cat command:

To list all open ports or currently running ports including TCP and UDP in Linux, we will use netstat, is a powerful tool for monitoring network connections and statistics.

1. -l – prints only listening sockets
2. -n – shows port number
3. -t – enables listing of tcp ports
4. -u – enables listing of udp ports

You can also use ss command, a well known useful utility for examining sockets in a Linux system. Run the command below to list all your open TCP and UCP ports:

Make it a point to read through the man pages of the commands above for more usage information.

In summary, understanding the concept of ports in computer networking is very vital for system and network administrators. You can as well go through this netstat guide with simple, precise and well explained examples.

Last but not least, get in touch with us by sharing other methods for listing open ports in Linux or asking a question via the response form below.

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How to Check Open Ports in Linux

During the troubleshooting of services running on a Linux system, checking open ports is one of the tasks any user or administrator should consider performing. If a service is expected to be running but for some reason it’s not, then most likely the port associated with that service is closed and should be opened.

In this tutorial, we will demonstrate how to check open ports in a Linux from the command line.

1) Check open ports using ss command

The Linux ss command gives you detailed insights on open ports and listening sockets. It draws information from the Linux kernel and is more preferred to the netstat command which has been deprecated.

To display listening TCP connections, run the command

Sample output

l — Shows listening sockets

t — Stands for TCP port

To display listening UDP connections, issue the command

Sample output

u — Stands for UDP port

To display both tcp and udp, process name

p — List process name that opened sockets

To print out all socket connections, simply use the ss command in its default format

Sample output

2) Check open ports using netstat command

The netstat command is a powerful command tool that is used for checking open TCP and UDP ports alongside other attributes. To check open ports, issue the command:

Sample output

Let’s take a closer look at the command options:

p — Displays the Procees ID associated with a service or Program name

n — Displays the numerical number of the port running e.g 3306 for mysqld, and 22 for sshd.

l — Shows listening sockets

t — Displays TCP connections

u — Displays UDP connections

3) Check open ports using the lsof command

The lsof command is a network command tool that can also be used to check open ports in a Linux system. To display open ports, issue the command

Sample output

If you wish to display open sockets, use the lsof command and pipe the output to grep as shown:

Sample output

To view all TCP connections execute :

Sample output

To display all UDP connections run the command:

Sample output

4) Check open ports using the Nmap utility

Nmap is a free and opensource network scanning tool usually used for reconnaissance in ethical hacking for discovering open ports of remote systems. By default, Nmap does not come installed on your system. To install Nmap, issue the command

To scan for open TCP ports, run the command

Sample output

To scan for open UDP ports, run the command:

Sample output

Wrapping up

Those are the linux commands and tools used for port scanning to check open ports in a Linux system. As always, your feedback is most welcome. If you have other ideas on how to check open ports, do get in touch with us.

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