What does the -tulpn option mean for netstat?

Question

For finding out which ports of the machine are being opening by which services, I used:

netstat -tulpn

I checked the man page for netstat command, but I found nothing about this option. What's the meaning of the -tulpn option?

Answer 1

As answered in https://serverfault.com/questions/387935/whats-the-difference-betwen-the-single-dash-and-double-dash-flags-on-shell-comm, in a Linux command line;

A single hyphen can be followed by multiple single-character flags.

A double hyphen prefixes a single multi-character option.

If you look at netstat man page, you will see that (Note that, netstat -tulpn is equivalent to netstat -t -u -l -p -n):

--tcp|-t

--udp|-u

-l, --listening
   Show only listening sockets.  (These are omitted by default.)

-p, --program
   Show the PID and name of the program to which each socket belongs.

--numeric, -n
   Show numerical addresses instead of trying to determine symbolic host, port or user names.

So, your command is equivalent to the following long form also:

netstat --tcp --udp --listening --program --numeric

Answer 2

In addition to man netstat you can type info netstat to get a shorter summary and longer explanation:

NETSTAT(8)                      Linux Programmer's Manual                      NETSTAT(8)

NAME
       netstat  -  Print  network connections, routing tables, interface statistics, mas‐
       querade connections, and multicast memberships

SYNOPSIS
       netstat [address_family_options] [--tcp|-t] [--udp|-u] [--raw|-w] [--listening|-l]
       [--all|-a]  [--numeric|-n]  [--numeric-hosts]  [--numeric-ports] [--numeric-users]
       [--symbolic|-N] [--extend|-e[--extend|-e]]  [--timers|-o]  [--program|-p]  [--ver‐
       bose|-v] [--continuous|-c]

For -t -u -l -p -n above you see --tcp, --udp, --listen, --program and --numeric without having to scroll.

Scrolling down you can see verbose explanations.

Answer 3

Looks like you were looking for the man page for netstat(8).

Linux.die.net has man pages for seemingly all Linux tools. See below the man page for netstat(8) which should answer your question.

https://linux.die.net/man/8/netstat