== How I use ssh's connection sharing feature

Following on [[the basic overview SshConnectionSharing]], here's how I
use OpenSSH's connection sharing feature.

First, since I hate programs that don't exit when I want them to, I
don't let _ssh_ automatically create connection masters. Instead I
always explicitly create them myself, so that I can do so in a way that
harmlessly parks them in the background. So while I set a _ControlPath_
(to a value mentioned in the [[previous entry SshConnectionSharing]]),
I leave _ControlMaster_ set to _no_, the default.

When I want to create a master _ssh_, I have a script that boils down
to:

> _ssh -M -f -o "BatchMode yes" $HOST exec sleep 120_

You might wonder about the '_sleep 120_'.

One of the peculiarities of how I use connection sharing is that so far
I always do it to hosts that I also have persistent sessions to. These
persistent sessions pin the master _ssh_ in place whether or not the
master _ssh_ itself is still doing anything, so the _sleep_ does two
things here. First, it keeps the master _ssh_ going long enough for my
real sessions to start, and second, it means that if and when I later
tear down all of my real sessions to the host, the master _ssh_ will
also exit because the _sleep_ has long since finished.

(Ideally there would be a _ssh_ option for 'keep running N seconds after
the last session closes to see if a new subordinate shows up'.  Then I
could set that to 120 seconds or so and just use '_/bin/true_' as the
command that the master _ssh_ runs.)

In actual practice I don't create master _ssh_ instances by hand.
Instead I do it from my X startup file, which (vastly simplified)
winds up looking like:

>  ssh-master host1
>  sleep 1  # give it time to come up
>  ssh host1 x-app-1 &
>  ssh host1 x-app-2 &
>  ....

(And then anything else that I want to do on host1 later will also get
the benefits of using the existing connection.)

Among other things, this approach has the benefit that it's easy to
add. I didn't need to change anything that my X startup script was
already doing; I just inserted an additional command early on. (And then
took it out again the first time I tried it, when it turned out to cause
various problems.)