Network Port Querying Script

Hey there,

The script I've put together here was originally written to meet a certain demand. That demand was actually my own, but that's beside the point ;)

This script should come in useful for you if you ever need to query a port and find out what's going on with it (like who's using it and/or what process id is associated with it). It's simple to invoke (taking only the port number as its argument) and produces information that can be a great aid in troubleshooting network connection issues.

If you refer back to this previous post you can check out a small walkthrough regarding how to query a port using lsof and/or the proc commands. This script uses lsof also, but combines it with netstat to produce output in an easy to read format, while grabbing a little more information in the process. Assuming we call it portquery, it can be invoked like this:

host # ./portquery 22 <--- Let's just see what's going on with SSH

and it will produce output for you like the following. Note that it produces a formatted output block for every single process connected to a port. On a high-traffic machine, checking SSH might produce a few pages of output. This is what it looks like when it's run:

Port 22 Information :
        Service = sshd
        PID = 469
        User = root
        Protocol = TCP
        Status = LISTEN
Port 22 Information :
        Service = sshd
        PID = 469
        User = jimmy88
        Protocol = TCP
        Status = LISTEN

...and the list goes on to print out information blocks for every PID attached to that port. This script has been a great help for me not only in that it makes a manual process automatic, but also in that it's easy for other non-admins to read.

Here's hoping you have some use for it :)

Best Wishes,





This work is licensed under a
Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License

#!/bin/ksh

#
# 2007 - Mike Golvach - eggi@comcast.net
# 
# Usage: portquery [port number]
#
# Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License
#

trap 'exit' 1 2 3 9 15
if [ $# -ne 1 ]
then
 echo "Usage: $0 portNumber"
 exit 1
fi

portnumber=$1

/bin/netstat -a |grep -w "$portnumber" >/dev/null 2>&1

if [ $? -ne 0 ]
then
 echo "Nothing's listening on - or using - port $portnumber"
 exit 1
fi

/usr/local/bin/lsof 2>&1|grep -v "^lsof:"|grep -w $portnumber 2>&1|while read x
do
 portinfo=`echo $x|awk '{print $1 " " $2 " " $3 " " $4 " " $5 " " $6 " " $7 " " $8 " " $9 " " $10}'`
 echo "Port $portnumber Information :"
 echo " Service = `echo $portinfo|awk '{print $1}'`"
 echo " PID = `echo $portinfo|awk '{print $2}'`"
 echo " User = `echo $portinfo|awk '{print $3}'`"
 echo " Protocol = `echo $portinfo|awk '{print $8}'`"
 echo " Status = `echo $portinfo|awk '{print $10}'|sed 's/(//'|sed 's/)//'`"
done

, Mike

linux unix internet technology