23.12.  Upgrading an Existing System

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The following sections only apply to upgrading Red Hat Enterprise Linux between minor versions, for example, upgrading Red Hat Enterprise Linux 6.4 to Red Hat Enterprise Linux 6.5 or higher. This approach is not supported for upgrades between major versions, for example, upgrading Red Hat Enterprise Linux 6 to Red Hat Enterprise Linux 7.
In-place upgrades between major versions of Red Hat Enterprise Linux can be done, with certain limitations, using the Red Hat Upgrade Tool and Preupgrade Assistant tools. See Chapter 37, Upgrading Your Current System for more information.
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.


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.

23.12.1.  Upgrading Using the Installer


In general, Red Hat recommends that you keep user data on a separate /home partition and perform a fresh installation. For more information on partitions and how to set them up, refer to Section 9.13, “Disk Partitioning Setup”.
If you choose to upgrade your system using the installation program, any software not provided by Red Hat Enterprise Linux that conflicts with Red Hat Enterprise Linux software is overwritten. Before you begin an upgrade this way, make a list of your system's current packages for later reference:
rpm -qa --qf '%{NAME} %{VERSION}-%{RELEASE} %{ARCH}\n' > ~/old-pkglist.txt
After installation, consult this list to discover which packages you may need to rebuild or retrieve from sources other than Red Hat.
Next, make a backup of any system configuration data:
su -c 'tar czf /tmp/etc-`date +%F`.tar.gz /etc' 
su -c 'mv /tmp/etc-*.tar.gz /home'
Make a complete backup of any important data before performing an upgrade. Important data may include the contents of your entire /home directory as well as content from services such as an Apache, FTP, or SQL server, or a source code management system. Although upgrades are not destructive, if you perform one improperly there is a small possibility of data loss.


Note that the above examples store backup materials in a /home directory. If your /home directory is not a separate partition, you should not follow these examples verbatim! Store your backups on another device such as CD or DVD discs or an external hard disk.
For more information on completing the upgrade process later, refer to Section 35.2, “Finishing an Upgrade”.
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