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How to check which process is using a TCP or UDP port

lsof [root@arlsmail1 conf.d]# lsof -i :110 COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME dovecot 1453 root 24u IPv4 22310 0t0 TCP *:pop3 (LISTEN) dovecot 1453 root 25u IPv6 22311 0t0 TCP *:pop3 (LISTEN) netstat # netstat -planet | grep :110 tcp 0 0 0.0.0.0:110 0.0.0.0:* LISTEN 0 22310 1453/dovecot tcp6 0 0 :::110 :::* LISTEN 0 22311 1453/dovecot