1.2 About ULN Channels

ULN provides more than 100 unique channels, which support the i386, x86_64, IA64, and the 64-bit Arm architectures, for releases of Oracle Linux 4 update 6 and later and Oracle VM 2.1 and later.

You can choose that your system remain at a specific OS revision, or you can allow the system to be updated with packages from later revisions.

You should subscribe to the channel that corresponds to the architecture of your system and the update level at which you want to maintain it. Patches and errata are available for specific revisions of Oracle Linux, but you do not need to upgrade from a given revision level to install these fixes. ULN channels also exist for MySQL, Oracle VM, Oracle Ksplice, OCFS2, RDS, and productivity applications.

The following table describes the main channels that are available.

Channel	Description
`_latest`	Provides all the latest versions of the packages in a distribution, including any errata that are also provided in the patch channel. If no vulnerabilities have been found in a package, the package version might be the same as that included in the original distribution. For other packages, the version is the same as that provided in the patch channel for the highest update level. For example, the `ol6_``arch``_latest` channel for Oracle Linux 6 Update 3 contains a combination of the `ol6_u3_``arch``_base` and `ol6_u3_``arch``_patch` channels.
`_archive`	Provides older versions of packages that are added to a parent channel. The `_archive` suffix is usually added to the channel that it hosts archive packages for. For example, the `_latest` channels have equivalent `_latest_archive` channels to host older versions of packages that have been updated in the `_latest` channels. Packages are moved to an archive channel when newer versions of the same packages are added to the parent channel. This helps to keep the metadata for the parent channel manageable and also keeps the overall size of the channel down to a minimum. If you require an earlier version of a package, you can subscribe to the equivalent `_archive` channel to obtain it. When performing an installation or downgrade, you must specify the version of the package that you wish to install. Installing packages from an `_archive` channel may result in your system running software that has since been patched for security related issues. This could open your system up to vulnerabilities that could be exploited for malicious purposes.
`_base`	Provides the packages for each major version and minor update of Oracle Linux and Oracle VM. This channel corresponds to the released ISO media image. For example, there is a base channel for each of the update level of an Oracle Linux release . Oracle does not publish security errata and bug fixes on these channels.
`_patch`	Provides only those packages that have changed since the initial release of a major or minor version of Oracle Linux or Oracle VM. The patch channel always provides the most recent version of a package, including all fixes that have been provided since the initial version was released.
`_addons`	Provides packages that are not included in the base distribution, such as the package that you can use to create a local yum repository on Oracle Linux.
`_oracle`	Provides freely downloadable RPMs from Oracle that you can install on Oracle Linux, such as ASMLib and Oracle Instant Client.
`_optional`	Provides optional packages for Oracle Linux 7 that have been sourced from upstream. This channel includes most development packages (`*-devel`).
`_developer`	Provides packages that can be used to set up test and development environments for Oracle Linux. Packages released in this channel include tools that can be useful for developers and test engineers when setting up an environment.
`_preview`	Provides packages that are still under development at Oracle and are made available as technical previews for developer and test engineer usage. These packages are not for use in a production environment and are not supported by Oracle.
`_developer_EPEL`	Provides a mirror of the packages that are available on the EPEL (Extra Packages for Enterprise Linux) repository. The packages hosted in this channel are available for Oracle Linux users but are unsupported by Oracle.

Other channels may also be available, such as _beta channels for the beta versions of packages.

As each new, major version or minor update of Oracle Linux becomes available, Oracle creates new base and patch channels for each supported architecture to distribute new packages. The existing base and patch channels for the previous versions or updates remain available and do not include the new packages. The _latest channel distributes the latest possible version of any package, and tracks the top of the development tree independently of the update level.

Caution

You can choose to maintain your system at a specific update level of Oracle Linux and selectively apply errata to that level by subscribing the system to the _base and _patch channels and unsubscribing it from the _latest channel. However, patches are not added to the _patch channel for previous updates of Oracle Linux after a new update has been released. For example, after the release of Oracle Linux 7 Update 1, no further errata will be released on the ol7_x86_64_u0_patch channel.

Oracle recommends that you keep you system subscribed to the _latest channel. If you unsubscribe from the _latest channel, your system will become vulnerable to security-related issues when a new update is released.

For more information about the channels available for any system that you have registered with ULN, see Section 4.1, “ULN Channel Subscription Management”.