CentOS Continuous Release

The CentOS Continuous Release repository (“CR”) was first introduced for CentOS 5.6, and currently exists for both CentOS 5 and CentOS 6. The CR repo is intended to provide package updates which have been released for the next point release upstream (from RHEL) which has not yet been officially released by CentOS yet due to delays around building, testing, and seeding mirrors for a new point release. For example, this means that once RedHat releases RHEL 5.8, CentOS will include package updates from 5.8 base and updates in CentOS 5.7 CR repo until the time that CentOS is able to complete the release of CentOS 5.8. For admins, this means less time without important security updates and the ability to be on the latest packages released in the latest RHEL point release.

Details on the CR Repo

What’s included in CR and how might it affect your current CentOS installs? At this point, the CR repo is used only for package updates which are part of the next upstream point release. For example, for CentOS 5.7, once Red Hat releases RHEL 5.8, the CR repo will contain updates from upstream base and updates repos. When a new update for RHEL 5.8 is released, it will be built in the CentOS build system, go through a relatively minimal amount of QA by the CentOS QA team, and then will be pushed to the CentOS 5.7 CR repo. This process will continue until the time that CentOS releases its own 5.8 release. Once CentOS releases 5.8, the CR repo will be cleared out until the time that RedHat releases the next (5.9) point release.

The CR repo is not enabled by default, so it is up to a system administrator to enable it if desired. That means, by default, you won’t see packages added to the CR repo. Installing the repo is very easy as it’s now part of the CentOS extras repository which is enabled by default. To enable CR, you simply have to:

yum install centos-release-cr

If you don’t have CentOS Extras enabled, you can browse into the extras/ directory for the release of CentOS you’re currently running and download and install the centos-release-cr package by hand, or manually create a centos-cr.repo in /etc/yum.repos.d/

In my opinion, unless you have an internal process for testing/pushing updates, you should absolutely be using the CR repo. Even if you do have your own local processes for updates, I would consider the CR repo to be part of CentOS updates for all intents and purposes, and pull your updates from there for testing/release. The packages in the CR repo can fix known security issues which without the CR repo you won’t have access to until the next CentOS point release -- and that can sometimes take longer than we’d like!

A New Proposal: Include CR by Default

In a recent post to the CentOS Developers list, Karanbir Singh proposed moving the CR repo into the main release for 6.x. What this would mean is for CentOS 6.x and onward, we would see the base OS and ISO directories be updated for each point release, but in general, updates would be pushed to a central 6/ directory, basically incorporating CR into what is currently considered updates/.

This proposal is different from the current CR setup in that it incorporates CR into the release by default, and puts less reliance on the old point release model. This will help ensure that people are always running the latest security updates as well as take a bit of pressure off of CentOS developers and QA team when trying to build, test, and release the next point release. If the package updates are already released and in use, point releases become less important (though still useful for new installs).

Incorporating CR more into the main release doesn’t mean that point releases will go away completely. They will still include updated base packages and ISO images, typically with installer bug fixes and/or new and updated drivers. In general, I see this as a good move: it means more people will be getting security updates by default instead of waiting during the time lapse between upstream RHEL releases and the time it takes for CentOS to rebuild, test, and release that point release. Having those packages available by default is great, especially for those admins who don’t pay close attention and wouldn’t otherwise enable the CR repo. It should be noted that at this point, the incorporation of CR into the main release is only being discussed for CentOS 6.x onward and won’t change anything in the 5.x releases where people will still need to manually opt-in to the CR packages.

References:
http://wiki.centos.org/AdditionalResources/Repositories/CR
http://lists.centos.org/mailman/listinfo/centos-cr-announce
http://lists.centos.org/pipermail/centos-devel/2011-November/008268.html

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