Stock Enterprise Linux packages can get pretty far out of date compared to their respective upstream projects. While Red Hat backports security fixes, new features are rarely added. This approach results in a very stable overall operating system, but can be frustrating to users when a new upstream feature is needed.

IUS stands for Inline with Upstream Stable. Our packages are fundamentally different from their stock counterparts. Our packages track the latest upstream versions of their respective software. There is an inherent risk with this approach; new upstream versions may introduce bugs that users of stock packages will never have to deal with. That said, we stand behind the quality of our packages, and work hard to find and resolve issues before packages are promoted to the stable repos. IUS users are forfeiting a small part of their system stability in order to get the new features they need. By using IUS packages, you implicitly agree to this trade off. This risk can be largely mitigated by participating in early testing using a non-production environment.

Don't Overwrite Stock Packages

IUS provides only safe replacement and parallel installable packages. Because of this, users can subscribe to IUS with no surprises; IUS packages will never overwrite stock packages. Only explictly chosen packages will be installed. You can enjoy the stability of Enterprise Linux for the majority of the system but still utilize the latest PHP, Python, MySQL, and more.

Release Policy

Updates for our existing packages are first released in the testing repositories. If no issues are reported after about two weeks, the updated packages will be promoted to the stable repositories. Please note, we reserve the right to promote package sooner if warranted.

This release policy does not not apply to new packages that have yet to be added to the stable repositories. When a new package is requested, the requester must agree to test the package. Once the requester confirms that everything works as expected, the package is eligible to be added to the stable repositories.

Naming Convention

IUS packages are typically named in the following format.


A similar format can be seen with some EPEL packages such as python34 and zabbix22. Using alternative names from stock packages has several benefits.

The only drawback to this naming format is that you can't directly upgrade from stock packages to IUS packages. Considering all the factors, we feel that the benefits far outweigh this inconvenience.

In addition to appending the major and minor version numbers, most IUS packages also have a "u" suffix. We started using that suffix in 2010 when Red Hat announced that RHEL 5.6 would be adding a package named php53 to the base repositories. This conflicted with our existing php53 package, so we knew we had to make a change. David Strauss suggested on our mailing list that we add a "u" suffix to prevent the name conflict. We liked the idea, and proceeded with implementing it. At the time, we thought it would be a one-time fix. In 2013, Red Hat released a product called Software Collections (RHSCL). Some of the packages that were offered overlapped with IUS packages. We were concerned that we would face more package name conflicts, but were relieved to hear that RHSCL would not be enabled by default. However, Red Hat later decided to add the mysql55 SCL packages to the base RHEL 5 repository. The SCL metapackage mysql55 had the same name as our existing mysql55 package. We evaluated renaming our mysql55 package to mysql55u to avoid the name conflict, but we were not able to find a solution that provided seamless upgrades. Since then, we have decided to add the "u" suffix to all our new packages to keep from getting in the same situation again.