If you want to see what processes are listening on what ports these you can use the linux command lsof and netstat. Below are a few good examples. You need to be root or use sudo to see processes that you don’t own.
Show what processes are using port 80
lsof -i TCP:80
Output
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
apache2 3369 www-data 4u IPv6 410048 0t0 TCP *:http (LISTEN)
apache2 3370 www-data 4u IPv6 410048 0t0 TCP *:http (LISTEN)
apache2 3372 www-data 4u IPv6 410048 0t0 TCP *:http (LISTEN)
apache2 12140 root 4u IPv6 410048 0t0 TCP *:http (LISTEN)
apache2 27614 www-data 4u IPv6 410048 0t0 TCP *:http (LISTEN)
apache2 27615 www-data 4u IPv6 410048 0t0 TCP *:http (LISTEN)
apache2 27654 www-data 4u IPv6 410048 0t0 TCP *:http (LISTEN)
apache2 27792 www-data 4u IPv6 410048 0t0 TCP *:http (LISTEN)
apache2 30098 www-data 4u IPv6 410048 0t0 TCP *:http (LISTEN)
apache2 30099 www-data 4u IPv6 410048 0t0 TCP *:http (LISTEN)
apache2 30100 www-data 4u IPv6 410048 0t0 TCP *:http (LISTEN)
root@util:~#
Listing processes on a MAC (port 22)
lsof -i4TCP:22
Output
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
Cyberduck 3887 mike 132u IPv6 0x9c24bd554cfdc3e3 0t0 TCP 10.10.0.14:53962->dev.com:ssh (ESTABLISHED)
Cyberduck 3887 mike 144u IPv6 0x9c24bd555473fea3 0t0 TCP 10.11.0.10:53770->dev.com:ssh (ESTABLISHED)
Cyberduck 3887 mike 145u IPv6 0x9c24bd5549389923 0t0 TCP 10.10.0.14:53977->dev.com:ssh (ESTABLISHED)
Cyberduck 3887 mike 146u IPv6 0x9c24bd5559a803e3 0t0 TCP 10.10.0.14:58802->10.3.8.1:ssh (ESTABLISHED)
ssh 16962 mike 3u IPv4 0x9c24bd553fc5a82b 0t0 TCP 10.10.0.14:55981->dev:ssh (ESTABLISHED)
ssh 17375 mike 3u IPv4 0x9c24bd553a95363b 0t0 TCP 10.10.0.14:60429->dev:ssh (ESTABLISHED)
list of port numbers that are listening and what application it is
netstat -plnt
Output
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 0.0.0.0:3306 0.0.0.0:* LISTEN 2840/mysqld
tcp 0 0 0.0.0.0:54321 0.0.0.0:* LISTEN 1409/sshd
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 1409/sshd
tcp 0 0 0.0.0.0:25 0.0.0.0:* LISTEN 2146/master
tcp6 0 0 :::80 :::* LISTEN 3369/apache2
tcp6 0 0 :::54321 :::* LISTEN 1409/sshd
tcp6 0 0 :::22 :::* LISTEN 1409/sshd