Upstart

[Patrick Goetz]

Scott James Remnant wrote:
> You might have forgotten to plug your USB
> mouse in this boot; or maybe your cat has chewed the ethernet cable
> overnight and it won't come up, etc.
>

Actually, it was my gerbil that frequently chewed through the ethernet 
cable, but then the cat ate the gerbil, so that bug has been resolved, 
so to speak.


> D-Bus is used to communicate with the init daemon, and one of the method
> calls you may make is to emit an event.  The event name is simply a
> string, and the arguments an array of strings.  There's no need to
> configure Upstart to accept certain events, you just make them up as you
> go along.
> 

Thanks for the detailed response, this is all starting to make sense. 
So if service Z can't start until services A,B, and C have already 
started the /etc/init/Z.conf file would contain the line:

   start on (A started and B started and C started)
?

And if D alternatively replaces A and C, then this becomes

   start on ((A started and B started and C started) or
             (B started and D started))
?


One last question. I'm curious about the technical details of how this 
is implemented; i.e. what blocks Z until A,B, and C have started?  Does 
upstart or some process simply make a list of /\/etc\/init\/(.+)\.conf/ 
and then poll through the list in a loop looking to see if the 'start 
on' conditions have already been met => send a startup $1 signal to 
init, remove $1 from the list whenever it does?