Linux Administration Cookbook

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An arguably better way of determining which process is using which port is to use the lsof command. I say arguably because it's not usually installed by default, though it is extremely handy and powerful.

If we use lsof and check for commands using port 22, we get the following list:

$ sudo lsof -i :22COMMAND  PID    USER   FD   TYPE DEVICE SIZE/OFF NODE NAMEsshd     877    root    3u  IPv4  17409      0t0  TCP *:ssh (LISTEN)sshd     877    root    4u  IPv6  17479      0t0  TCP *:ssh (LISTEN)sshd    4262    root    3u  IPv4  43232      0t0  TCP centos1:ssh->gateway:36116 (ESTABLISHED)sshd    4265 vagrant    3u  IPv4  43232      0t0  TCP centos1:ssh->gateway:36116 (ESTABLISHED)

If you don't want to print hostnames (centos1 in the above example) and port names (ssh above) you can use the following ...