Re: Switching the default startup method
On Mon, Aug 24, 2009 at 07:54:04PM +0200, Luk Claes wrote:
> Wouter Verhelst wrote:
> > On Mon, Aug 24, 2009 at 03:34:51PM +0200, Raphael Hertzog wrote:
> >> Well, both are deterministic but they do not decide of the ordering in the
> >> same way and it's just easier for our brains to represent a number-based
> >> sequence.
> > Sorry, but dependency-based boot systems are *not* deterministic.
> > Let's assume the following:
> > - initscript a depends on b
> > - initscript c declares that it wants a to be started first if it is
> > installed, but that it is not a problem if it isn't installed.
> > Now we may have either of the following situations, depending on whether
> > the user does or does not install recommendations:
> > - b is started first, then a, then c
> > - b is started, and c too. The order depends on coincidence, since there
> > is no relationship between the two
> > If initscript c should actually declare a dependency on initscript b,
> > then you have a bug that the maintainer may find himself hard-pressed to
> > reproduce, simply because he does have the package containing initscript
> > a installed.
> If there is a bug in the dependencies of c, then there is indeed a
> problem that should get fixed. I don't see what you try to prove with
> that though?
That the system is not deterministic ;-)
I'm not saying this kind of bug will occur; indeed, given that Petter
has been working on this for a long time, I would be surprised if there
were many such bugs in Debian.
However, we cannot be sure whether this is or is not the case until
we've tried; and in cases where the system does break, people should be
able to disable it, at the very least until the bug is found and fixed
and their system can be made usable again with the new option enabled.
The biometric identification system at the gates of the CIA headquarters
works because there's a guard with a large gun making sure no one is
trying to fool the system.