determining ports that are in use

albockiole · 01-23-2002, 12:33 AM

There was a similar post earlier about blocking a port over a LAN, but how can you find out which ports are in use, so you can block the offending port?

I seem to remember reading somewhere that there was a program you could run in the terminal that would report what ports were in use (and could also refresh at a user-defined interval), but I can't remember what that program is.

Anyone out there know how I can determine what ports are in use on my computer?

thanks in advance...

blb · 01-23-2002, 01:35 AM

netstat -nf inet will show all current connections, TCP and UDP. netstat -anf inet will add listening ports to this; basically, the LISTEN port is where a server (or daemon) is sitting, waiting for a connection.

If you want to know which process is listening to a port, use lsof. For example:

Code:

$ netstat -anf inet
...
tcp        0      0  127.0.0.1.1033         *.*                    LISTEN

so I want to know who's listening on port 1033, I'd use lsof:

Code:

$ sudo lsof -i :1033
...
netinfod    207 root    6u  inet 0x01a9cd1c      0t0  TCP localhost:1033 (LISTEN)

(the interesting one being the LISTEN state again, the others are currently connected). In this case, 1033 is the NetInfo daemon (netinfod).

Gwyrrdin · 01-23-2002, 05:13 AM

this command works great....

Read the manpage for more options...

Code:

% lsof -i -n -P

Gives a very complete overview of all your networkconnections.

Good Luck

Gwyrrdin

albockiole · 01-25-2002, 12:35 PM

Thanks for the tips everyone...

It turns out the program I wanted to block is using a random port everytime it starts up, so it's making it very difficult to do so.

Oh well, at least I know how to take care of the static ones.

Thanks...

01-23-2002, 12:33 AM	#1
albockiole Prospect Join Date: Jan 2002 Location: Boston Posts: 10	determining ports that are in use There was a similar post earlier about blocking a port over a LAN, but how can you find out which ports are in use, so you can block the offending port? I seem to remember reading somewhere that there was a program you could run in the terminal that would report what ports were in use (and could also refresh at a user-defined interval), but I can't remember what that program is. Anyone out there know how I can determine what ports are in use on my computer? thanks in advance...

01-23-2002, 01:35 AM	#2
blb All Star Join Date: Jan 2002 Location: CO, USA Posts: 908	netstat -nf inet will show all current connections, TCP and UDP. netstat -anf inet will add listening ports to this; basically, the LISTEN port is where a server (or daemon) is sitting, waiting for a connection. If you want to know which process is listening to a port, use lsof. For example: Code: $ netstat -anf inet ... tcp 0 0 127.0.0.1.1033 . LISTEN so I want to know who's listening on port 1033, I'd use lsof: Code: $ sudo lsof -i :1033 ... netinfod 207 root 6u inet 0x01a9cd1c 0t0 TCP localhost:1033 (LISTEN) (the interesting one being the LISTEN state again, the others are currently connected). In this case, 1033 is the NetInfo daemon (netinfod).

01-23-2002, 05:13 AM	#3
Gwyrrdin Prospect Join Date: Jan 2002 Location: Leeuwarden/ The Netherlands Posts: 21	this is what I use this command works great.... Read the manpage for more options... Code: % lsof -i -n -P Gives a very complete overview of all your networkconnections. Good Luck Gwyrrdin __________________ OS X= Beauty with Brains!

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01-25-2002, 12:35 PM	#4
albockiole Prospect Join Date: Jan 2002 Location: Boston Posts: 10	Thanks for the tips everyone... It turns out the program I wanted to block is using a random port everytime it starts up, so it's making it very difficult to do so. Oh well, at least I know how to take care of the static ones. Thanks...