All you experienced is exactly how it is supposed to be.
Yum-priorities does the following:
ALLWAYS use version of package from repo with lesser priority number.
For all OTHER packages, use version of package with lesser priority number.
I use it like this:
Priority plugin is active always. If I hit dependency problem like you
did, there are two things you can do:
a) do not install package with unresolved dependency
b) run install with "--disableplugin=*prior*" and IGNORE that external
repo will mess with your system, replacing packages yum-priorities is
installed to protect. For smaller insignificant packages I would select
b), but very carefully.
Ljubomir
Nick wrote:
Hello,
I'm a relatively new user of CentOS 5.5. The CentOS wiki advises the use of yum
priorities if you use more than the base repositories, specifically with RPMForge:
http://wiki.centos.org/AdditionalResources/Repositories/RPMForge
(I have yum-3.2.22-26.el5.centos and yum-priorities-1.1.16-14.el5.centos.1)
As I gather has been stated before on the centos list [1], it also implies that
yum-priorities isn't a great solution (quoting Seth Vidal), but stops
short of outlining what exactly is wrong with yum-priorities (YP) and why it's
still recommended. In fact it goes on to say:
as of yet, no real world problems have been reported with regard to the
'yum-priorities' plugin
So, I experienced a real-world problem (more details in [2]):
- set CentOS base with priority 1
- set RPMForge with priority 2
- yum check-update was ok
- yum update seemed ok, prompted to proceed, then aborted half way.
It aborted because of an unresolvable dependency from an RPMForge package, where
the package which satisfies it hidden by an older version in the base repo.
Specifically:
perl-Module-Install-0.92-1.el5.rf needed perl-Archive-Tar >= 1.44
At first I thought RPMForge must be broken, because there seemed to be nothing
which would satisfy the dependency, just this:
$ yum list --showduplicates perl-Archive-Tar
perl-Archive-Tar 1.30 centos-base
RPMForge appears to have nothing at all. Later I inferred yum-priorities was
hiding it from view, because with --noplugins, yum would admit that indeed the
required perl-Archive-Tar-1.44 did exist in RPMForge:
$ yum list --showduplicates --noplugins perl-Archive-Tar
perl-Archive-Tar 1.30 centos-base
perl-Archive-Tar 1.44 rpmforge
So RPMForge was not broken, I just have an pathological case of yum-priorities.
Of course, I know this is what yum-priorities is designed to do, and that it
isn't perfect. I have two suggestions, however - but they seem a bit obvious,
so before I file them on the yum issue tracker I'd like to check I've not missed
anything.
Firtly, the fact that yum+YP hides packages so completely they don't seem to be
present can be confusing, and it'd be nice if that could be fixed so that
--showduplicates will report the presence of packages which won't be installed
because of YP.
However, the bigger problem is that yum does *not* seem to be able to detect the
kind of unresolvable dependency problem I experienced. Therefore it happily
starts the update process, only to abort with an error half way through, leaving
my system essentially broken. Neither does yum check-update warn me about this
risk.
My choice seems to be:
- don't use yum-priorities, but get into a muddle when base OS packages get
replaced, or
- do use it, but at the risk of breaking my (possibly production) server at an
unpredictable moment entirely outside my control (as described).
Couldn't yum check-update and yum update detect the dependency problem and warn
me at a point I can still back off?
For example, in a case like the one above, couldn't yum update check the
dependencies available and refuse to proceed, telling me something like this?
perl-Module-Install-0.92-1.el5.rf needs perl-Archive-Tar >= 1.44, but
perl-Archive-Tar-1.44 from the 'rpmforge' repo cannot be used due to
the presence of perl-Archive-Tar-1.30 the higher priority repo 'centos-base'.
See [link to documentation] for possible ways to resolve this problem.
Thanks,
Nick
---
1. http://thread.gmane.org/gmane.linux.centos.general/86563
2. An example of when yum_priorities bites included here:
http://www.noodlefactory.co.uk/~nick/wu-lee/Notes/YumPrioritiesPitfalls
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