Editing Centos Repos (section)

== Known Problem Repositories ==
These repositories are known to cause issues due to large scale of replacement of base packages with little or no warning. Use extreme caution if you choose to use these repositories, and consider using an alternative above.

'''Atomic Repo''' - (See https://www.atomicorp.com/channels/) Atomicorp has commercial products as well as free repositories with later version of PHP, MySQL and many other packages. Some additional packages that may not be available elsewhere include hunspell, snort, and zabbix. They also provide Plesk.<class="lmtxt orange" style="padding:0pt;text-align:left;">

Be particularly careful about the Atomic repo as they enable their repo by default when installed, and overwrite user changes in the configuration without notice when the release package is updated. Atomic will replace many core packages as configured when installed. Many CentOS users have had problems after enabling this repo, as a forum search will reveal. Even removing packages installed from this repository may leave the system in an unusable state. You've been warned.

'''City-Fan''' - Supplies repos for various CentOS/RHEL versions and all appear to have no regard for overwriting packages from base/updates without warning. Enabled by default, contains lots of packages that overwrite base packages. That includes various system libraries including libcurl and will break yum as soon as it's installed! Do not use.

Be particularly careful about the City-Fan repo as they enable their repo by default when installed. City-Fan will replace many core packages as configured when installed and those packages often have a different structure than the CentOS ones making them difficult if not impossible to remove cleanly. Even removing packages installed from this repository may leave the system in an unusable state. You've been warned.

'''Jason Litka''' - Utter Ramblings Repository - No longer appears to be maintained.

'''RPMForge/RepoForge''' - This is a dead project. Not maintained. DO NOT USE.

'''Webtatic Repo''' - Provides updated packages with later versions of PHP, MySQL, and other packages. IUS or SCL are better alternatives.

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mostly copied from https://wiki.centos.org/AdditionalResources/Repositories