mjhjmtu

I found someone keeps a SSH session alive by

ssh -f -D $port $SSH_HOST "
 if [ -f ~/.tunnel ]; then
 rm ~/.tunnel;
 fi;
 while [ ! -f ~/.tunnel ]; do
 echo > /dev/null;
 done
" &

and terminates a SSH session by

ssh $SSH_HOST "touch ~/.tunnel" 

1. Is the way of using a file the same way as a pid file? Can the way be used for more or general cases?




2. Do we really need to use the way of using a file to keep a SSH session alive and terminate it? Is there a better way to do that?

Thanks.

Simple Improvements

The technique allows you to kill a connection from the remote machine. I would suggest a couple of changes

• Add a sleep in the while loop, there's no point throwing CPU time on waiting


• Invert the process. Touch the file at the start and delete it to kill the session. This does give you an option to include a PID in the file if you want.

Do you need this?

If you only want to kill the session I would avoid the method in your question and use:

SSH -N -D $port $SSH_HOST &

This will set up a connection without a shell as a background task (-N disables the shell and & makes it a background task).

You can get the (local) PID for this with $! and kill it with kill

Eg:

SSH -N -D $port $SSH_HOST &
TUNNEL_PID=$!

# Do some other stuff

kill $TUNNEL_PID

Besides what @PhilipCouling has written, there exists an odd but effective little utility, Spinner, useful when an interactive terminal session is to be kept open. You run it on the remote host. It doesn't do much, but sends a dummy data packet back to the local client every N seconds (I use N = 120, for example). The dummy keeps the connection alive.

Not sure that this is the sort of thing you wanted, but there it is.