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Old 01-23-2002, 12:33 AM   #1
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...
albockiole is offline   Reply With Quote
Old 01-23-2002, 01:35 AM   #2
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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:

$ netstat -anf inet
tcp        0      0         *.*                    LISTEN
so I want to know who's listening on port 1033, I'd use lsof:

$ 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).
blb is offline   Reply With Quote
Old 01-23-2002, 05:13 AM   #3
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...
% lsof -i -n -P
Gives a very complete overview of all your networkconnections.

Good Luck

OS X= Beauty with Brains!
Gwyrrdin is offline   Reply With Quote
Old 01-25-2002, 12:35 PM   #4
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.

albockiole is offline   Reply With Quote

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