#!/bin/bash
TPORT="5001"
/usr/bin/nohup /root/tunnel/tunnel.sh root my_host_here $TPORT 22 &> $HOME/tunnel/rssh.out &

#!/bin/bash

user=$1
rip=$2
rport=$3
lport=$4

while [[ 1 ]]; do
   if [ -e $HOME/tunnel/$lport.pid ]; then
      pid=$(cat $HOME/tunnel/$lport.pid)
   else
      pid=1
   fi

   ps | grep $lport | grep $pid | grep -v $HOME/tunnel/tunnel.sh | grep -q ssh
   if [[ $? -ne 0 ]]; then
      echo $(date) opening reverse tunnel from $rip:$rport to 127.0.0.1:$lport
      ssh -o "ExitOnForwardFailure yes" -R $rport:127.0.0.1:$lport $user@$rip -N &
      echo $! > $HOME/tunnel/$lport.pid
   fi

   sleep 60
done

ps | grep $lport | grep $pid | grep -v $HOME/tunnel/tunnel.sh | grep -q ssh

user=$1    # Assign the first command line argument to the "user" variable (remote user)
rip=$2     # Assign the second command line argument to the "rip" variable (remote IP)
rport=$3   # Assign the third command line argument to the "rport" variable (report port)
lport=$4   # Assign the fourth command line argument to the "lport" variable (local port)

# Loop forever
while [[ 1 ]]; do

   # Check for the existence of a file called $lport.pid (eg: 22.pid if you set lport to 22), located in $HOME/tunnel/
   if [ -e $HOME/tunnel/$lport.pid ]; then

      # If that file exists, read the contents into the "pid" variable
      pid=$(cat $HOME/tunnel/$lport.pid)

   else

      # If that file does not exist, just set the "pid" variable to the number 1
      pid=1
   fi


   # That $lport.pid file contains the process ID (PID) for the previously-opened reverse ssh tunnel.  What
   # we're going to do now is test that PID.  Is it still running?  Is it associated with the right process?  Etc.

   # ps returns a list of currently running processes on the system
   # "|" lets you send the output from one command to the input of another
   # grep lets you search some text for a specific string or pattern

   # So the below command means:
   # 1) "ps" - List all running processes
   # 2) "| grep $lport" - Search those processes for the local port we're opening
   # 3) "| grep $pid" - Search those matches for the PID we're interested in
   # 4) "| grep -v tunnel.sh" - "-v" inverts the search, so this gets rid of any lines that match tunnel.sh (that would be this script itself)
   # 5) "| grep -q ssh" - "-q" does a quiet match, so it doesn't print anything out, it just searches for the string "ssh" and sets the exit status to 0=success or else=failure

   # The end result is the exit status gets set to 0 if a process matching $lport, $pid, and "ssh" but NOT tunnel.sh was found, and any other number if it wasn't

   ps | grep $lport | grep $pid | grep -v $HOME/tunnel/tunnel.sh | grep -q ssh

   # If the exit status was not 0, it means the process was not found, so the tunnel must not be open, so open it back up
   if [[ $? -ne 0 ]]; then

      # Print out a comment for the log file
      echo $(date) opening reverse tunnel from $rip:$rport to 127.0.0.1:$lport

      # Open up the tunnel
      ssh -o "ExitOnForwardFailure yes" -R $rport:127.0.0.1:$lport $user@$rip -N &

      # Dump the PID of that ssh command into $lport.pid for the next iteration of the loop
      echo $! > $HOME/tunnel/$lport.pid

   fi

   # Wait a minute before repeating
   sleep 60
done