LINUX COMMANDS

netstat [options] [delay]

TCP/IP command. Show network status. Print information on active sockets, routing tables, interfaces, masquerade connections,
or multicast memberships. By default, netstat lists open sockets. When a delay is specified, netstat will print new information every
delay seconds.

Linux Commad Options:
The first five options (-g, -i, -M, -r, and -s) determine what kind of information netstat should display.
-g, --groups
Show multicast group memberships.
-i, --interface[=name]
Show all network interfaces, or just the interface specified by name.
-M, --masquerade
Show masqueraded connections

-r, --route
Show kernel routing tables.
-s, --statistics
Show statistics for each protocol.
-a, --all
Show all entries.
-A family, --protocol=family
Show connections only for the specified address family. Accepted values are inet, unix, ipx, ax25, netrom, and ddp. Specify multiple families in a comma-separated list.
-c, --continuous
Display information continuously, refreshing once every second.
-C Print routing information from the route cache.
-e, --extend
Increase level of detail in reports. Use twice for maximum detail.
-F Print routing information from the forward information database (FIB). This is the default.
-l, --listening
Show only listening sockets.
-n, --numeric
Show network addresses, ports, and users as numbers.
--numeric-hosts
Show host addresses as numbers, but resolve others.
--numeric-ports
Show ports as numbers, but resolve others.
--numeric-users
Show user ID numbers for users, but resolve others.
-N, --symbolic
Where possible, print symbolic host, port, or usernames instead of numerical representations. This is the default behavior.
-o, --timers
Include information on network timers.
-p, --program
Show the process ID and name of the program owning the socket.
-t, --tcp
Limit report to information on TCP sockets.
-u, --udp
Limit report to information on UDP sockets.
-v, --verbose
Verbose mode.
-w, --raw
Limit report to information on raw sockets.

Examples:

netstat -tup    List active connections to/from system

netstat -tupl    List internet services on a system