Notes about open source software, computers, other stuff.

Script to tunnel RDP connections through stepping stone server using SSH

In order to connect to the servers at work we need to connect through a stepping stone host (via SSH). Since some of the servers are MS Windows machines which can be managed via the Remote Desktop Protocol (RDP), this traffic needs to be tunneled over SSH as well.
I wrote the following bash script to automate setting up the tunnel. It sets some default variables and then looks for an available port between 1234 and 1254 (chosen completely arbitrarily) and uses it for the tunnel. Then it uses the rdesktop program to start the RDP connection.

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#!/bin/bash
#
# This script makes an ssh tunnel to a stepping stone server
# and uses it to start an rdesktop connection to the machine 
# given as the first argument of the script. 
#
# (C) L.C. Karssen
# $Id: winremote.sh,v 1.14 2010/02/10 13:03:08 lennart Exp $
#
 
# User-configurable variables
ssh_username=your_steppingstone_username_here
steppingstone=steppingstone.your_company.com
rdesktop_username=your_windows_username_here
rdesktop_domain=your_windows_domain_here
rdesktop_opts="-z -g 1024x768 -a 16"
rdesktop_port=3389 # This is the standard MS rdesktop port
 
 
# For ordinary users it should not be necessary to change anything below this line. 
# Some functions:
usage()
{
    cat <<EOF
Usage:
    $program [options] rdesktop_hostname 
 
Make a remote desktop connection through an SSH tunnel.
 
Options: 
    -h, --help                                   print this help message
    -s, --steppingstone steppingstone_hostname   set other stepping stone host
                                                   (default: $steppingstone)
    -t, --timeout sec                            set timeout (default: 1)
    -v, --verbose                                verbose output
     --version                                   print version
 
Note that some customisations need to be made in the first few lines of this 
script (e.g. user names and other defaults)
EOF
}
 
program=`basename $0`
 
# Command line option parsing. Shift all options 
verbose=
timeout=1
 
while [ $# -gt 0 ]
do 
    case $1 in
	-v | --verbose | -d | --debug ) 
	    verbose=true
	    ;;
	--version )
	    echo '$Revision: 1.14 $'
	    exit 0
	    ;;
	-t | --timeout ) 
	    shift
	    timeout="$1"
	   if [ $timeout -lt 1 ]; then
	       timeout=1
	   fi
	   if [ $verbose ]; then
	       echo "Timeout set to $timeout"
	   fi
	   ;;
	-s | --steppingstone ) 
	   shift
	   steppingstone="$1"
	   if [ $verbose ]; then
	       echo "Steppingstone server is $steppingstone"
	   fi
	   ;;
	-h | --help ) 
	   usage
	   exit 0
	   ;;
	-*) 
	   echo "$0: invalid option $1" >&2
 	   usage
	   exit 1
	   ;;
	*) 
	   break
	   ;;
    esac
    shift
done
 
# Server name (as seen on the steppingstone) that we want to connect to:
rdesktop_server=$1 
 
################### Config done, let's get to work ########################
 
# Simple usage description
if [ "$rdesktop_server" == "" ]; then
    echo "Error: No rdesktop host given" >&2
    usage
    exit 1
fi
 
# Find a free port on the local machine that we can use to connect through
min_port=1234
max_port=1254
used_ports=(`netstat -tan | awk '{print $4}' | grep 127.0.0.1 | awk -F: '{print $2}' | sort -g`)
if [ $verbose ]; then
    echo "Used ports are: ${used_ports[@]}"
fi
 
# In the next line we first print the $used_ports as an array, but with 
# each port on a single line. This is then piped to an awk script that 
# puts all the values in an array and subsequently walks through all ports 
# from $min_port to $max_port in order to find the first port that is not 
# in the array. This port is printed.
local_port=`printf "%i\n" ${used_ports[@]} | \
    awk -v minp=$min_port -v maxp=$max_port \
    '{ array[$1]=1 } END { for (i=minp; i<=maxp; i++) { if (i in array) continue; else { print i; break } } }'`
if [ "$local_port" == "" ]; then
    echo "Error: No ports free! Exiting..." >&2
    exit 2
fi
if [ $verbose ]; then
    echo "Selected port was: $local_port"
fi
 
# Create tunnel:
if [ $verbose ]; then
    echo "Creating SSH tunnel..."
fi
ssh_opts="-f -N -L"
ssh $ssh_opts $local_port:$rdesktop_server:$rdesktop_port \
    $ssh_username@$steppingstone 
 
# Allow the ssh tunnel to be established
sleep $timeout
 
# Abort if tunnel has not been established
pidof_ssh=`pgrep -f "ssh $ssh_opts $local_port"`
if [ "$pidof_ssh" == "" ]; then
    echo "Error: Timeout while establishing tunnel" >&2
    echo "Exiting..."
    exit 3
fi
 
# Make rdesktop connection
if [ $verbose ]; then
    echo "Opening Remote desktop connection to $rdesktop_server..."
fi
rdesktop $rdesktop_opts -u $rdesktop_username -p - \
    -d $rdesktop_domain localhost:$local_port
 
# Clean up tunnel
if [ $verbose ]; then
    echo "Cleaning up SSH tunnel with pid $pidof_ssh and local port $local_port"
fi
kill $pidof_ssh

3 Comments

  1. webugz

    It’s helpful. Thanks for the work.

  2. Prasad

    Is there an example where I want to run Word, Excel and Power Point files in a sequence and close each one and then start them back in a loop. I need to remote desktop to a remote server to accomplish this, appreciate your help if u can provide me a script for the same.

    I am not a scripting guru

    • LCK

      Hi Prasad,

      Looking at the command line options of rdesktop there doesn’t seem to be way to tell the remote machine to start a certain program after connecting. Maybe you could try to write a script (a batch file or something in Powershell) that runs when you login (maybe in the Startup folder in your Start menu) and opens the MS Office files for you.

      Good luck!

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