Rogelio wrote:
I'm following the instructions on this URL
http://wiki.centos.org/HowTos/RT_3.4.x_On_CentOS_4.x
and came across the part that said
"WARNING: RT overwrites some packages from the base distribution, especially mod_perl"
How exactly do I "protect" the RT repository?
It links to the "ProtectBase" program
http://wiki.centos.org/PackageManagement/Yum/ProtectBase
...but what do I mod to protect this RT repository?
protectbase (or priorities) plugins are what you want to use to prevent 3rd party repositories from replacing packages in your CentOS Base repos.
Priorities is the better of the plugins.
What priorities (or protectbase) does is block installing or updating packages that are in protected repositories from non-protected repositories.
So let's assume you have one repo named Base and you add a new repo named X
Base contains a package called foo-1.0.0.i386.rpm ... and X contains 2 packages named foo-1.1.0.i386.rpm and bar-1.1.0.i386.rpm
The purpose of both the priorities and protectbase plugins is to allow you to keep foo from Base and get bar from X.
If you only have 2 repos, protectbase and priorities are equally effective.
Now, if we add repo Y ... things get a bit more tricky. Protectbase only has protect=1 and protect=0. That means there are 2 groups of repos with protectbase, protected and non-protected. All repos in a specific group are equal (not protected from each other) ... and all repos in the protected group are protected from all repos in the non-protected group.
Let's put the following packages in repo Y foo-1.2.0.i386.rpm and bar-1.2.0.i386.rpm and example-1.2.0.i386.rpm
With no plugins installed and all repos enabled if we do this:
yum install foo bar example
Then we get this installed:
foo-1.2.0.i386.rpm bar-1.2.0.i386.rpm example-1.2.0.i386.rpm
(all from repo Y because those are the LARGEST packages)
NOW ... if we have protectbase installed and Base is set to protect=1 and both X and Y are set to protect=0 ... we would get this installed:
foo-1.0.0.i386.rpm bar-1.2.0.i386.rpm example-1.2.0.i386.rpm
(because Base is protected, and if a package is in Base ... in this case foo, it is not updated by a non protected group. But since both X and Y are in the non-protected groups, bar and example both come from Y)
NOW ... if we install priorities, we get to pick a priority for each repo (and we remove protectbase plugin and no longer need protect= in the repo config file). We would use priority=N (where N is 1-99) to set a priority. Lets set Base (which contains files that we want to keep because they are stable and designed to work together) to priority=1 (the highest priority). We can set X to priority=10 and Y to priority=20 (I picked these arbitrarily, but it is good to leave space between priorities so you can add repos in between later).
In this example ... if we did the same yum install command we would get:
foo-1.0.0.i386.rpm bar-1.1.0.i386.rpm example-1.2.0.i386.rpm
This is because foo comes from the highest priority repo where it exists (Base ... priority=1) and bar comes from the highest priority repo where it exists (X ... priority=10) and example comes from the highest priority repo where it exists (Y ... priority=20).
Note that a lower number in priority means a higher priority position ... meaning that Priority=1 is the highest position and Priority=99 is the lowest priority position.
Protectbase and Priorities are redundant and you only need one or the other ... and since priorities can do everything that protectbase does and offer more groups, priorities is recommended.
Now ... for more on priorities and protectbase ... see this link: