16.13. Upgrading an Existing System
Although anaconda provides an option for upgrading from earlier major versions of Red Hat Enterprise Linux to Red Hat Enterprise Linux 6, Red Hat does not currently support this. More generally, Red Hat does not support in-place upgrades between any major versions of Red Hat Enterprise Linux. (A major version is denoted by a whole number version change. For example, Red Hat Enteprise Linux 4 and Red Hat Enterprise Linux 5 are both major versions of Red Hat Enterprise Linux.)
In-place upgrades across major releases do not preserve all system settings, services or custom configurations. Consequently, Red Hat strongly recommends fresh installations when upgrading from one major version to another.
The installation system automatically detects any existing installation of Red Hat Enterprise Linux. The upgrade process updates the existing system software with new versions, but does not remove any data from users' home directories. The existing partition structure on your hard drives does not change. Your system configuration changes only if a package upgrade demands it. Most package upgrades do not change system configuration, but rather install an additional configuration file for you to examine later.
Note that the installation medium that you are using might not contain all the software packages that you need to upgrade your computer.
16.13.1. The Upgrade Dialog
If your system contains a Red Hat Enterprise Linux installation, a dialog appears asking whether you want to upgrade that installation. To perform an upgrade of an existing system, choose the appropriate installation from the drop-down list and select
Figure 16.24. The Upgrade Dialog
Software you have installed manually on your existing Red Hat Enterprise Linux system may behave differently after an upgrade. You may need to manually reinstall or recompile this software after an upgrade to ensure it performs correctly on the updated system.