How to check if a port is occupied in CentOS

The following column centos tutorial will introduce to you how to check whether the port is occupied in CentOS. I hope it will be helpful to friends in need!

CentOSCheck whether a port is occupied
This article introduces the method of checking whether a port is occupied in Linux, and the use of netstat command Tips, interested friends can refer to it.

Use the command:

netstat -tunlp

will display all ports and all corresponding programs. Use the grep pipe to filter out the desired key fields.

Programs related to port 22 occupancy:

Code example:

[root@leiwan tmp]# netstat -tunlp |grep 22 
tcp        0      0 0.0.0.0:42957               0.0.0.0:*                   LISTEN      2230/rpc.statd 
tcp        0      0 0.0.0.0:22                  0.0.0.0:*                   LISTEN      2443/sshd 
tcp        0      0 127.0.0.1:631               0.0.0.0:*                   LISTEN      2292/cupsd 
tcp        0      0 :::22                       :::*                        LISTEN      2443/sshd 
tcp        0      0 ::1:631                     :::*                        LISTEN      2292/cupsd 
tcp        0      0 :::57609                    :::*                        LISTEN      2230/rpc.statd 
udp        0      0 0.0.0.0:5353                0.0.0.0:*                               2211/avahi-daemon 
udp        0      0 0.0.0.0:631                 0.0.0.0:*                               2292/cupsd 
udp        0      0 0.0.0.0:37167               0.0.0.0:*                               2230/rpc.statd 
udp        0      0 0.0.0.0:52291               0.0.0.0:*                               2211/avahi-daemon 
udp        0      0 0.0.0.0:68                  0.0.0.0:*                               2207/dhclient 
udp        0      0 0.0.0.0:710                 0.0.0.0:*                               2230/rpc.statd 
udp        0      0 :::39834                    :::*                                    2230/rpc.statd

Check the occupancy of a certain port: lsof -i:port number

Code example:

1  [root@www ~]# lsof -i:21 
3  COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME 
4  pure-ftpd 2651 root 4u IPv4 7047 TCP *:ftp (LISTEN) 
5  pure-ftpd 2651 root 5u IPv6 7048 TCP *:ftp (LISTEN)

This shows that port 21 is being used by pure-ftpd and the status is listen.

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