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[edlug] yum_priorities on RHEL



Hello,


Anyone who's used RPMForge on CentOS might have come across this page, with its
somewhat ambiguous endorsement of yum_priorities but lacking a clear alternative:

 http://wiki.centos.org/AdditionalResources/Repositories/RPMForge

The other week I ran into one of the pitfalls of using more than one repository
with yum_priorities...  and more recently I hit yet another.


First problem: say you're using CentOS5.3, with yum_priorities installed, and
the CentOS repositories set at a higher priority to RPMForge's.

If a upgrade package appears in RPMForge (say perl-Module-Install-0.92-1.el5.rf)
with a new dependency on another (say perl-Archive-Tar >= 1.44), but that
package already exists in CentOS base at an insufficient version (say v1.30),
your upgrade will break, telling you that there is an unsatisfied dependency -
yum doesn't even seem to be able to tell there *is* an RPMForge version unless
you use the --noplugins option.

The conclusions for use of 3rd party yum repositories seem to be:

 - avoid, where possible
 - if not, stick to one, preferably the biggest
 - when absolutely necessary, punch holes in higher priority repositories with
   exclude=<pkgname>

The pgdg repository for postgres suggests this last tactic, and all its
non-postgres RPMs seems to be mirroring the CentOS base repository. See:

 https://public.commandprompt.com/projects/pgcore/wiki/Howto

It doesn't seem ideal, however, since dependencies can change, meaning your
exclude list is going to have to be fixed at unpredictable intervals.



Second problem: if you manage both CentOS and RHEL machines, a strategy like the
above which uses yum_priorities cannot be used uniformly across them both, as
you might think.

 From http://article.gmane.org/gmane.linux.rpm.rpmforge.user/1270

> Because of the way the yum-rhn-plugin works, priorities can't be used with 
> Red Hat systems. They do provide the yum-protectbase package which isn't as 
> flexible as priorities, but the Red Hat repos are protected, so any repo that
> is not protected can't overwrite packages from a protected repo.

This doesn't quite work in the case I'm trying to support: we have our
self-built rpms repo, plus base, rpmforge, and pgdg for postgres.  This to work
on CentOS, but now we need to install on RHEL...


I wondered if anyone here had encountered these issues, and if there was a way
to avoid them? (Besides the obvious "don't use so many repositories.")

Specifically, I wonder if there is something better than protectbase which works
on RHEL?

Cheers,

N
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