Linux Discovery ports

Mac
sudo lsof -iTCP -sTCP:LISTEN


Linux
List used ports 
$netstat -tulpn | grep LISTEN

tcp        0      0 127.0.0.1:5939          0.0.0.0:*               LISTEN      -                  
tcp        0      0 127.0.0.53:53           0.0.0.0:*               LISTEN      -                  
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      -                  
tcp        0      0 127.0.0.1:631           0.0.0.0:*               LISTEN      -                  
tcp6       0      0 :::80                   :::*                    LISTEN      -                  
tcp6       0      0 :::22                   :::*                    LISTEN      -                  
tcp6       0      0 ::1:631                 :::*                    LISTEN      -

List process that using port
You like to knows who is using port 80, then

$sudo lsof -i :80
apache2   965     root    4u  IPv6  26650      0t0  TCP *:http (LISTEN)
apache2 13794 www-data    4u  IPv6  26650      0t0  TCP *:http (LISTEN)
apache2 13795 www-data    4u  IPv6  26650      0t0  TCP *:http (LISTEN)
apache2 13796 www-data    4u  IPv6  26650      0t0  TCP *:http (LISTEN)
apache2 13797 www-data    4u  IPv6  26650      0t0  TCP *:http (LISTEN)
apache2 13798 www-data    4u  IPv6  26650      0t0  TCP *:http (LISTEN)


Second option

$sudo netstat -peanut | grep ":80"
tcp6       0      0 :::80                   :::*                    LISTEN      0          26650      965/apache2

Setting apache
$vi /etc/apache2/apache2.conf

#       /etc/apache2/
#       |-- apache2.conf
#       |       `--  ports.conf
#       |-- mods-enabled
#       |       |-- *.load
#       |       `-- *.conf
#       |-- conf-enabled
#       |       `-- *.conf
#       `-- sites-enabled
#               `-- *.conf