Problems Updating Packages
You may have landed here because of errors like the following:
~]# yum upgrade Loaded plugins: fastestmirror, security Determining fastest mirrors * base: mirrors.kernel.org * extras: mirror.chpc.utah.edu * updates: mirror.steadfast.net http://mirrors.kernel.org/centos/5.11/os/x86_64/repodata/repomd.xml: [Errno 14] HTTP Error 404: Not Found Trying other mirror.
This is because on March 31st, all of the EL5 derivatives are now end of life. It is time to update to EL6 or EL7.
If you are unable to update immediately, but would like to get your OS as up to date as possible, then CentOS users can update their repositories from mirror.centos.org to vault.centos.org in /etc/yum.repo.d/CentOS-*.conf . For Scientific Linux, you will want to use the following link in your repository files: http://ftp.scientificlinux.org/linux/scientific/obsolete/511/$basearch/SL/.
We have migrated many CentOS/RHEL/Scientific Linux systems and would be happy to assist if you need help!
-Eric