Open a Listening port on Linux

Updated: Feb 2

How to open a port on Linux is a common question when testing a firewall related problem. Today we will use nc command to open a tcp port manually on Linux and check if this port is working or not.

Use nc or ncat to open a port on Redhat/Centos Linux

Nc or ncat is delivered as part of nmap-ncat rpm in RHEL/CentOS which we can install using yum or dnf. Use --listen with --port to open a port using nc command. In the below example we open port 1234

[root@centos-8 ~]# nc --listen --source-port 1234

Open another terminal of this server and check port status

[root@centos-8 ~]# netstat -ntlp | grep 1234

tcp 0 0* LISTEN 28983/nc

tcp6 0 0 :::1234 :::* LISTEN 28983/nc

As you see port 1234 is listening for both IPv4 and IPv6. To only use IPv4 use -4 with the above command

[root@centos-8 ~]# nc --listen --source-port 1234 -4

Next on another terminal, you can check the port status for port 1234

Check the port status

[root@centos-8 ~]# netstat -ntlp | grep 1234

tcp 0 0* LISTEN 29329/nc

Use nc to open a port on Ubuntu Linux

We can use this command to get port open.

# nc -lk port number

Related Post:

Linux: 5 ways to Check a remote port is open

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