A patch is an update. It incorporates changes in source code. Patches are normally applied to specific software components, such as the kernel, or a service, such as vsFTP. Patches may fix bugs, address security issues, or incorporate new features. As an administrator, you're responsible for testing the new software, making sure that it addresses any problems before your users see them on their systems. Patches can be released from developer or some 3rd parties.
It can be apply for,
1. Security Fixes
2. Service Upgrades
3. Bug Fixes
4. Kernel Patches
5. Kernel Upgrades
There are several sources for patches and upgrades. The best source is generally the upgrade repository preconfigured for your distribution. However, there is often a delay when distribution developers process updates from other sources, such as the kernel, or services, such as the Apache Web server.
Red Hat Enterprise Linux Updates :
If you want RHEL, you may have already taken the following steps:
1. Register with the Red Hat Network at https://rhn.redhat.com.
2. Examine available RHEL distributions.
3. Purchase one or more subscriptions for RHEL.
4. Activate your subscription(s).
5. Download or acquire the CDs for RHEL.
6. Install RHEL on your computers.
7. Update your system through the Red Hat Network.
The Red Hat Update Agent:
RHEL's Update Agent, also known as up2date, provides a complete system for updating the RPM packages installed on your RHEL computers. It allows you to register with and monitor appropriate Red Hat repositories for updates.