netstat -tunlp will display all ports and all corresponding programs, and the grep pipeline can filter out the desired key fields. List the programs occupied by port 22 [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 port: lsof -i: port number
| 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.
netstat -anp shows system port usage