[ILUG] ssh cleverness?

[Justin Mason]

Ronan Cunniffe writes:
> Brendan Halpin wrote:
> 
> >I'm puzzled, and more than a little impressed.
> >
> >However, if I have firefox running locally on the laptop, an
> >invocation of firefox on the work machine will not run it remotely,
> >but will cause the laptop firefox to fetch the relevant page. Very
> >clever[1]. But how does it do it? In particular, *what* knows that
> >I have firefox running on the X-server? Is it ssh? sshd? X?
> >Firefox? The FSM? 
> >
> Of *course* the FSM knows!  Eh, what *kind* of heretic are you trying to be?
> 
> Heh.  Have a look at /usr/bin/mozilla-firefox (or wherever it hides on 
> your box).  It's a shell script, and yes, you will be impressed - Grep 
> for 'check_running', or "xfeDoCommand(openBrowser".  This had me 
> scratching my head for a while too, once upon a time, and I still don't 
> know *why* they do this.

I'm pretty sure the trick is done using a Property on the X root display
or similar -- see 'xprop -root', for example.

X11 has a pretty good messaging system in there.  That hasn't stopped
GNOME and KDE reinventing the wheel on several occasions ;)

--j.