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Re: When to use pre-depends?



On 8 Sep 1996, Kai Henningsen wrote:

> maor@ece.utexas.edu (Guy Maor)  wrote on 05.09.96 in <Pine.SOL.3.93.960905130431.13405E-100000@brando.ece.utexas.edu>:
> 
> > Is the essentialness of a package a sufficient condition for using
> > pre-depends?
> 
> The difference in functionality between depends and pre-depends, as I  
> understand it, are that a pre-depends guarantees that your package won't  
> even be *unpacked* unless the pre-depends is already completely installed.  
> On the other hand, a depends only guarantees that the other package will  
> be completely installed before *configuration* of your package starts.

That's correct.

Pre-depends and essentialness are different things.  The first prevents
a package from existing in an unconfigured state (when dependencies
might not be satisfied).  The second prevents a package from being
removed.

In both cases the intent is the same: there should *always* be a
working version of the package installed.  So very few packages should
have one without the other.  A quick script gives:

adduser ess but not pre-dep and has dep
at pre-dep but not ess
libc5 pre-dep but not ess
modules pre-dep but not ess
ncurses3.0 ess but not pre-dep and has dep
perl pre-dep but not ess

All but two of these should have both or neither.  The only that look
correct are perl, because base includes a stripped version, and libc5,
which requires a working ld.so, but might be removed in favor of
libc6.

Note that packages in base are *not* automatically essential.  The key
point here is that the system is unusable, not hard to use.


Guy



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