To add an extra repository, place a definition file in the /etc/yum.repos.d/ directory on your system. Package providers make the definition files for their repositories available on their web sites.

	Definition File Extension
	The names of repository definition files end with .repo.

You must have root access to add a file to the definitions directory. To copy the definition file example.repo, type this command:

su -c 'cp example.repo /etc/yum.repos.d/'

At the prompt, enter the password for the root account.

The configuration file for each repository should include a gpgkey setting. This setting specifies the location of a public key that verifies the packages provided by that repository. This public key is automatically imported the first time that you install software from the repository. If the configuration file provided does not include this setting, refer to Section 7.2, “Manually Authorizing Package Sources”.

	Repositories and up2date Channels
	Starting with CentOS 3, and continuing in CentOS 4, the default yum repositories are automatically used as up2date channels. If you want to add other channels for up2date, you must manually configure up2date to use these channels. To do so, edit the /etc/sysconfig/rhn/sources file.

To manually add a public key to your rpm keyring, use the import feature of the rpm utility. To import the file GPG-PUB-KEY.asc, type the following command:

su -c 'rpm --import GPG-PUB-KEY.asc'

At the prompt, enter the password for the root account.

You may also import public keys directly from a web site. For example, to import the file GPG-PUB-KEY.asc on the web site www.therepository.com use this command:

su -c 'rpm --import http://www.therepository.com/GPG-PUB-KEY.asc'

At the prompt, enter the root password.

	Importing the CentOS Key on CentOS 3 and CentOS 4
	To add the CentOS public key to the rpm keyring on CentOS 3 systems, run the command: su -c 'rpm --import http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-3' For CentOS 4 systems use the command: su -c 'rpm --import http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-4'

Third-party packages should be compatible with these CentOS Project packages, unless the provider specifically states otherwise.

Always read the web site of the repository for information on package compatibility before you add it as a package source. Separate repository providers may offer different and incompatible versions of the same software. Third-party repositories may also provide alternative packages for software that is included in CentOS repositories.

Alternative packages may contain versions of the software that function differently from the version in the CentOS Project packages. Determine the benefits and potential incompatibilities before replacing CentOS Project packages with alternative versions.

	Incompatible Repositories
	If you configure your system to use incompatible repositories yum operations may fail.

Packages built for one version of CentOS are usually not compatible with other versions of CentOS. The web site of the provider should specifically state which versions of CentOS they support.

Old Versions of yum and Current Repositories

The data format for repository indexes changed with version 2.1 of yum. This was the version supplied with CentOS 4. Repository providers should specify the versions of CentOS that they support. To confirm that an unlabeled repository is compatible with CentOS 4 versions of yum, check that it has a sub-directory called repodata/. For CentOS 3 versions of yum, you are looking for the directory called headers/.

	CentOS compatible yum Repositories
	There are several repositories out there that are compatible with CentOS 3 and CentOS 4, but there are a couple that stand out as excellent in their compatability. The CentOS project highly recommends the repositories: Karanbir Singh's kbs-centos-extras Repository Dag Wieers' Repository Dries' Repository