"minit" point of view

[Erich Schubert]

Hi Martin,
> Or if init sends on SIGCHLD signals to another process.

I mentioned that more as "if it's not a detached process, init won't notice".
meaning that you can't use pid 1 as a generic monitoring thing, but
you need to make sure the processes you want to monitor become its
children.

> Yes, the issue gets a whole lot more complicated with parallel
> execution. FWIW, I think you only need to keep track of grey state
> per execution thread. You don't need to track which service
> requested which other service.

Keeping track of execution threads can become very complicated. Try to
avoid that.
I'd have trouble actually defining what an execution thread is...

> > Note that this information is useful for rollbacks, too.
> 
> I am not quite sure I picked up what rollbacks are.

undoing an action.
e.g. service a is to be restarted. So you need to bring down other
services; after the restart you need to bring them up again.

Or consider the case that service a depends on service b, so you start
service b, too.
Now the user requests service a to be shut down - why should you keep
service b running?

> I disagree. If the web search was configured for apache, installing
> roxen will break it. apache/apache2 is a special case because they
> are related.

Often it will, and the *package* usually will work with any web server
even remote.
I don't want to force it onto the user to take care of specifying the
depencenies. Whenever possible this should be handled automatically,
assuming that he has configured the apps appropriately...

That's why I want maintainers to be able to specify a dependency like
"depends on an alive webserver", and have the system translate the
virtual "webserver" to some real service. Kind of an alternatives
system. maybe even with update-alternatives --config

> I have yet to see an application that selects whichever one is
> available at run-time, or which can use both. If an application is

It's pointless to discuss wheter you have seen that. It's technically
possible, and someone might want it. Maybe it even exists, we just
havn't recognized it yet. So we should consider supporting it.

> > Speed reasons. I just want it to be started, but I don't
> > immedeately need it. Like postfix - you might want it to depend on
> > your dns service, but they can easily start at the same time.
> 
> So what happens when the DNS service fails to start?

The magically modified postfix server won't accept incoming
connections until the dns server replies, not losing any mail.

best regards,
Erich Schubert
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