How to find the PID of the process that is using specific port ?

This tutorial guides you on how to find the PID of the process that is using specific port. As you know that a port can be used by a single application at any point of time. Sometimes we may need to find which process is listening on specific port.

Find the PID of the process that is using specific port

In my case I had installed VNC server and started many VNC server sessions. And I wanted to kill the VNC process manually using PID and free the port which need to be used by another instance. Therefore it is important to find the PID of the process that is using specific port.

In this tutorial let’s see various approaches to find the process listening on a particular port in Ubuntu Linux.

Using netstat command

The netstat command is part of net-tools package. And it is widely used for this purpose. Let’s see how to use netstat command to list all TCP listening sockets, TCP connections, UDP connections with program ID or program name as shown below.

$ netstat -ltnup

(Not all processes could be identified, non-owned process info
 will not be shown, you would have to be root to see it all.)
Active Internet connections (only servers)
Proto Recv-Q Send-Q   Local Address           Foreign Address         State       PID/Program name
tcp        0              0        0.0.0.0:35993          0.0.0.0:*                     LISTEN      -
tcp        0              0        0.0.0.0:59003          0.0.0.0:*                     LISTEN      -
tcp        0              0        0.0.0.0:2049           0.0.0.0:*                     LISTEN      -
tcp        0              0        0.0.0.0:46305          0.0.0.0:*                     LISTEN      -
tcp        0              0        0.0.0.0:5900           0.0.0.0:*                     LISTEN      -
tcp        0              0        127.0.0.1:5901         0.0.0.0:*                     LISTEN      17186/Xtigervnc
tcp        0              0        127.0.0.1:5902         0.0.0.0:*                     LISTEN      17737/Xtigervnc
tcp        0              0        0.0.0.0:111            0.0.0.0:*                     LISTEN      -
tcp        0              0        0.0.0.0:49267          0.0.0.0:*                     LISTEN      -
tcp        0              0        127.0.0.53:53          0.0.0.0:*                     LISTEN      -

--------
---------

Note, the meaning of the options that we are using in the netstat command is below.

l – List only listening sockets
t – List TCP connections
n – addresses in a numerical form
u – List UDP connections
p – List PID/Program name

You can also use grep command to filter and check the PID information for the specific port alone.

For example,

$ netstat -ltnup | grep ':59'

(Not all processes could be identified, non-owned process info
 will not be shown, you would have to be root to see it all.)
tcp        0      0 0.0.0.0:59003           0.0.0.0:*               LISTEN      -
tcp        0      0 0.0.0.0:5900            0.0.0.0:*               LISTEN      -
tcp        0      0 127.0.0.1:5901          0.0.0.0:*               LISTEN      17186/Xtigervnc
tcp        0      0 127.0.0.1:5902          0.0.0.0:*               LISTEN      17737/Xtigervnc
tcp6       0      0 :::5900                      :::*                       LISTEN      -
tcp6       0      0 ::1:5901                     :::*                      LISTEN      17186/Xtigervnc
tcp6       0      0 ::1:5902                     :::*                      LISTEN      17737/Xtigervnc

lsof Command to find PID

The lsof command can be used list all open files.

For example,

$ lsof -i :5901 -i :5902

COMMAND     PID   USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
Xtigervnc 17186 ubuntu    7u  IPv4 176047      0t0  TCP localhost:5901 (LISTEN)
Xtigervnc 17186 ubuntu    8u  IPv6 176048      0t0  TCP ip6-localhost:5901 (LISTEN)
Xtigervnc 17737 ubuntu    7u  IPv4 181502      0t0  TCP localhost:5902 (LISTEN)
Xtigervnc 17737 ubuntu    8u  IPv6 181503      0t0  TCP ip6-localhost:5902 (LISTEN)

Use ss tool to get PID information

ss is another tool that can be used to investigate sockets and process information.

For example,

$ ss -ltnup 'sport = :5901'

Netid       State        Recv-Q       Send-Q             Local Address:Port              Peer Address:Port       Process
tcp         LISTEN       0            5                      127.0.0.1:5901                   0.0.0.0:*           users:(("Xtigervnc",pid=17186,fd=7))
tcp         LISTEN       0            5                          [::1]:5901                      [::]:*           users:(("Xtigervnc",pid=17186,fd=8))

u$ ss -ltnup 'sport = :5902'

Netid       State        Recv-Q       Send-Q             Local Address:Port              Peer Address:Port       Process
tcp         LISTEN       0            5                      127.0.0.1:5902                   0.0.0.0:*           users:(("Xtigervnc",pid=17737,fd=7))
tcp         LISTEN       0            5                          [::1]:5902                      [::]:*           users:(("Xtigervnc",pid=17737,fd=8))

Using fuser

You can also use fuser to identify processes using files and sockets in Linux system.

For example,

$ fuser -v 5901/tcp

                     USER        PID ACCESS COMMAND
5901/tcp:            ubuntu    17186 F.... Xtigervnc

$ fuser -v 5902/tcp

                     USER        PID ACCESS COMMAND
5902/tcp:            ubuntu    17737 F.... Xtigervnc

That’s it. You had learnt numerous approaches to get the process information of the process that is listening on a specific port.

Hope this article is helpful 🙂

Also See:

References

ubuntu documentation