How to check whether the port is occupied in centos

How to check whether a port is occupied in centos: 1. Use the netstat command to check the occupancy of all ports, the syntax is "netstat -tunlp"; 2. Use the lsof command to check the occupancy of the specified port, the syntax is " lsof -i:port number".

The operating environment of this article: centos 7 system, Dell G3 computer.

How to check whether the port is occupied in centos

1. Use the netstat command

The Linux netstat command is used to display the network status.

Using the netstat command allows you to know the network status of the entire Linux system.

Use the command:

netstat -tunlp

will display all ports and all corresponding programs, and use the grep pipeline to filter out the desired key fields.

Programs related to port 22 occupation:

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

2. Use the lsof command

lsof(list open files) is a tool that lists open files on the current system. In the Linux environment, everything exists in the form of files. Through files, you can access not only regular data, but also network connections and hardware. Therefore, such as Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) sockets, the system allocates a file descriptor to the application in the background. Regardless of the nature of the file, the file descriptor is the application Provides a common interface for interaction with the underlying operating system.

Check the occupancy of a certain port:

lsof -i:端口号

Code example:

[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)

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

Recommended tutorial: "centos tutorial"

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