Set enable=0 in a definition file to prevent yum from using that repository. The yum utility ignores any definition file with this setting.

To completely remove access to a repository:

By default, yum retains the packages and package data files that it downloads, so that they may be reused in future operations without being downloaded again. To purge the package data files, use this command:

su -c 'yum clean headers'

Run this command to remove all of the packages held in the caches:

su -c 'yum clean packages'

For CentOS-4 users, to clean the metadata files use this command:

su -c 'yum clean metadata'

When using these commands, at the prompt, enter the password for the root account.

Purging cached files causes those files to downloaded again the next time that they are required. This increases the amount of time required to complete the operation.

Yum functionality in version 2.4.x on CentOS 4 can now be extended through the use of yum plugins.

Enabling yum plugins: In order to use any plugins with yum, you must first edit the file /etc/yum.conf and add the following line:

plugins=1

Once plugins are enabled in yum.conf, you may install yum plugins and use them.

Some yum plugins are available as seperate rpm packages. Currently in CentOS-4 those are protectbase and fastestmirror. These plugins are highly recommended for CentOS-4 users who are using the default update method.

fastestmirror

The fastest mirror plugin is designed for use in repository configurations where you have more than 1 mirror in a repo configuration. It makes a connection to each mirror, timing the connection and then sorts the mirrors by fastest to slowest for use by yum.

If you are using the default CentOS configuration, and if you are not behind a proxy server, fastestmirror is highly recommended.

To install fastestmirror use this command:

su -c 'yum install yum-plugin-fastestmirror'

After fastestmirror is installed, make sure that it is enabled. Edit the file /etc/yum/pluginconf.d/fastestmirror.conf and ensure that it contains the following:

[main]
verbose = 0
socket_timeout = 3
enabled = 1
hostfilepath = /var/cache/yum/timedhosts.txt
maxhostfileage = 1

protectbase

The purpose of the protectbase plugin is to protect certian repositories from updates from other repositories. Repositories that are to be protected will not be updated by newer files from non protected repositories. This plugin is recommended for anyone who routinely enables 3rd party repositories, as these non-CentOS repositories may update certian system files, potentially causing your CentOS installation to become unstable.

To install the protectbase plugin, ensure that the CentOS extras repository is enabled (it is enabled by default) and issue this command:

su -c 'yum install yum-plugin-protectbase'

After the plugin is installed, make sure that it is enabled. Edit the file /etc/yum/pluginconf.d/protectbase.conf and ensure that it contains the following:

[main]
enabled = 1

Next you need to edit all .repo files in /etc/yum.repos.d/ and add either:

protect = 1

or

protect = 0

for each repository. Here is an example of protecting only the [base] and [update] repositories in the CentOS-Base.repo file:

[base]
name=CentOS-$releasever - Base
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os
#baseurl=http://mirror.centos.org/centos/$releasever/os/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos4
protect=1

#released updates 
[update]
name=CentOS-$releasever - Updates
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=updates
#baseurl=http://mirror.centos.org/centos/$releasever/updates/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos4
protect=1 

#packages used/produced in the build but not released
[addons]
name=CentOS-$releasever - Addons
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=addons
#baseurl=http://mirror.centos.org/centos/$releasever/addons/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos4
protect=0 

#additional packages that may be useful
[extras]
name=CentOS-$releasever - Extras
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=extras
#baseurl=http://mirror.centos.org/centos/$releasever/extras/$basearch/
gpgcheck=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos4
protect=0 

#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever - Plus
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=centosplus
#baseurl=http://mirror.centos.org/centos/$releasever/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos4
protect=0 

#contrib - packages by Centos Users
[contrib]
name=CentOS-$releasever - Contrib
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=contrib
#baseurl=http://mirror.centos.org/centos/$releasever/contrib/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos4
protect=0

	Adding protect= to all repositories
	You MUST add protect=0 to all repos in all .repo files in /etc/yum.repos.d/ or any repos that you have in /etc/yum.conf if you want them unprotected, otherwise they belong to the protect=1 group. As a general rule add either protect=0 or protect=1 to each and every repo.

When doing updates after editing your files, only repositories that have protect=1 group can update other protect=1 repositories. In our example, yum will only update the [base] or [update] directories with RPMs from [base] or [update]. If there were updated RPMs in the [addons] directory for packages in [base], they would not be updated.

With both the protectbase and fastestmirror yum plugins installed, you should get the fastest updates with maximum protection from accidental damage from 3rd party repositories.

yum-utils plugins

Please review those plugins and if you would like to install them for use, copy the plugin_name.conf file to /etc/yum/pluginconf.d/ and the plugin_name.py file to /usr/lib/yum-plugins/ to enable that specific plugin.