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How to get our assigned and free port number in Ubuntu

Asked by R.Lakshmi Narasimhan

I am trying to do some communication work for establishing a connection between systems through internet using C.For this i need to know the port addresses of my system which are free and which are assigned to processes.Please tell me whether there are any methods to find both of these categories.Also tell me is there any way to make the assigned user-defined port as free.

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R.Lakshmi Narasimhan (rlaknar) said : 		#1

Also please tell me is it possible to trace the port number of service providers of ip.

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fab-furnari (fab-furnari) said : 		#2

Try with netstat -lnp to see the used port on your machine and the apps using them.

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R.Lakshmi Narasimhan (rlaknar) said : 		#3

pl tell me any special commands available in Linux to find it

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R.Lakshmi Narasimhan (rlaknar) said : 		#4

can u tell me for make the user-defined used ports as free.

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fab-furnari (fab-furnari) said : 		#5

Sorry but I don't understand your proposal...try with a more exaustive explanation

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R.Lakshmi Narasimhan (rlaknar) said : 		#6

1) For my work i have used some user-defined ports in my program. I need to make it unassigned. How to do.Is it any way using commands?
2) How to get the port number of my service provider?
3)I cant understand the output of netstat -lnp command to find the port number.Is there any other way to find it?

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fab-furnari (fab-furnari) said : 		#7

1) The simplest way to reuse a port used by another program (if is this the question) is to kill the process using that port or set port not assigned by the IANA board (see http://www.iana.org/assignments/port-numbers)

2) If you want to know the port used by a service just see in netstat -lnp the field "PID/Program name".

3) try to nmap yourself :-D

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