Upgrading a Red Hat or CentOS system isn’t difficult. Just type yum update, it’s easy. So easy, in fact, that is quite possible to upgrade a system you didn’t intend to, or to upgrade a system further than was wanted, which is the subject of this post.

Point Upgrades

Yum update, used on a system which has not been updated for months or years, will cause hundreds of packages to be upgraded. It will also result in a point release upgrade. For example, a system running Red Hat/CentOS 6.2 might change to 6.5 after the update, or even to 6.7 or 6.9.

Although Red Hat maintains a strong compatibility between different versions of the same major release, the minor numbers are still important. They are quoted in compatibility matrices, and are a handy way to confirm patch levels. Knowing about the point change in advance would be useful. To check it, proceed as follows.

Example

Here is an example from a Red Hat 6.1 system I recently updated. How would the update change the version number ? The answer is: it would change to 6.9. Do a “yum list” on the “redhat-release-server” package and look at the installed and available versions.

# yum list redhat-release-server
Loaded plugins: product-id, rhnplugin
Installed Packages
redhat-release-server.x86_64                   6Server-6.1.0.2.el6                   @anaconda-RedHatEnterpriseLinux-201105101844.x86_64/6.1
Available Packages
redhat-release-server.x86_64                   6Server-6.9.0.4.el6                   rhel-x86_64-server-6

The installed version is confirmed as 6.1, while the proposed, ie. “available” version is clearly 6.9. When the yum update was later performed, over 500 packages were updated, and the Red Hat version did indeed change to Red Hat 6.9.