List open network ports

A few ways to list open ports

$ lsof -i

example

COMMAND    PID USER   FD   TYPE  DEVICE SIZE/OFF NODE NAME
kdeconnec 1671 john   10u  IPv6   27671      0t0  UDP *:1716 
kdeconnec 1671 john   11u  IPv6   27672      0t0  TCP *:1716 (LISTEN)
thunderbi 1712 john   36u  IPv4   28601      0t0  TCP Arach:46604->mail.com:imap2 (ESTABLISHED)
thunderbi 1712 john   50u  IPv4   25417      0t0  TCP Arach:46694->mail.com:imap2 (ESTABLISHED)
thunderbi 1712 john   51u  IPv4   25418      0t0  TCP Arach:46696->mail.com:imap2 (ESTABLISHED)
thunderbi 1712 john   65u  IPv4  871420      0t0  TCP Arach:48490->mail.com:imap2 (ESTABLISHED)
thunderbi 1712 john   80u  IPv4 1690593      0t0  TCP Arach:49032->mail.com:imap2 (ESTABLISHED)
java      2342 john   99u  IPv6   38225      0t0  TCP localhost:40834->localhost:4243 (ESTABLISHED)
firefox   3757 john   49u  IPv4 1809675      0t0  TCP Arach:58736->fra16s08-in-f206.1e100.net:https (ESTABLISHED)
firefox   3757 john   61u  IPv4 1809667      0t0  TCP Arach:35190->fra07s28-in-f238.1e100.net:https (ESTABLISHED)
firefox   3757 john   62u  IPv4 1816763      0t0  TCP Arach:43806->cache.google.com:https (ESTABLISHED)
firefox   3757 john   63u  IPv4 1809767      0t0  TCP Arach:59834->webcluster-ssl2.webpod5-cph3.one.com:https (ESTABLISHED)
firefox   3757 john   66u  IPv4 1816252      0t0  TCP Arach:35992->fra16s07-in-f10.1e100.net:https (ESTABLISHED)
firefox   3757 john   69u  IPv4 1779531      0t0  TCP Arach:55194->192.0.73.2:https (ESTABLISHED)

using netstat

$ netstat -lptu

example

Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 Arach:domain            *:*                     LISTEN      -               
tcp6       0      0 [::]:4242               [::]:*                  LISTEN      -               
tcp6       0      0 localhost:4243          [::]:*                  LISTEN      -               
tcp6       0      0 [::]:1716               [::]:*                  LISTEN      1671/kdeconnectd
udp        0      0 *:mdns                  *:*                                 -               
udp        0      0 *:56013                 *:*                                 -               
udp        0      0 Arach:domain            *:*                                 -               
udp        0      0 *:bootpc                *:*                                 -               
udp        0      0 *:ipp                   *:*                                 -               
udp6       0      0 [::]:1716               [::]:*                              1671/kdeconnectd
udp6       0      0 [::]:36429              [::]:*                              -               
udp6       0      0 [::]:mdns               [::]:*                              -

using netstat showing port numbers instead of service names

$ netstat -lptun

example

Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 127.0.1.1:53            0.0.0.0:*               LISTEN      -               
tcp6       0      0 :::4242                 :::*                    LISTEN      -               
tcp6       0      0 127.0.0.1:4243          :::*                    LISTEN      -               
tcp6       0      0 :::1716                 :::*                    LISTEN      1671/kdeconnectd
udp        0      0 0.0.0.0:5353            0.0.0.0:*                           -               
udp        0      0 0.0.0.0:56013           0.0.0.0:*                           -               
udp        0      0 127.0.1.1:53            0.0.0.0:*                           -               
udp        0      0 0.0.0.0:68              0.0.0.0:*                           -               
udp        0      0 0.0.0.0:631             0.0.0.0:*                           -               
udp6       0      0 :::1716                 :::*                                1671/kdeconnectd
udp6       0      0 :::36429                :::*                                -               
udp6       0      0 :::5353                 :::*                                -