how to check whether the ssh tunnel is up

[Damien Miller]

On Sat, 27 Apr 2013, Vincent Lin wrote:

> Hi damien,
> 
> Thanks for your reply. ExitOnForwardFailure=yes will exit the process if SSH
> tunnel failed to create. But what if it's OK?  Is there a way to know when
> it will be OK? I mean maybe it will cost some time, and when the tunnel is
> up, I can know it, or I can get the status all the time on the SSH client
> side, if it's possible. And what's the difference with or without -f, since
> I already create a  SSH daemon. Do I have to fork another process again?

The fork will happen once the tunnel is ready, so you can do something
like:

ssh -nNfoExitOnForwardFailure=yes \
    -oControlMaster=yes -oControlPath=~/.ssh/fwd%l-%r-%h-%p \
     -L1234:10.11.12.13:1234 user at host
if test $? -ne 0 ; then
	echo failed 2>&1
	exit 1
fi

# ... later, to clean up:
ssh -O exit -oControlPath=~/.ssh/fwd%l-%r-%h-%p user at host

These use the multiplexing socket to cleanly terminate the forwarding ssh
client. Have a look at the sections on '-f' in ssh(1) and the various
options in ssh_config(5) to see how they work together.

-d