EPEL
Extra Packages for Enterprise Linux (EPEL) is a volunteer-based community effort from the Fedora project to create a repository of high-quality add-on packages for Red Hat Enterprise (RHEL) and its compatible spinoffs such as CentOS or Scientific Linux. Fedora is the upstream of RHEL and add-on packages for EPEL are sourced from the Fedora repository primarily and built against RHEL.
EPEL有很多额外的包，centos的yum库里软件和rh的一样，EPEL里面有很多有用的软件。更多详情：
http://fedoraproject.org/wiki/EPEL
安装方法：
su -c ‘rpm -Uvh http://download.fedora.redhat.com/pub/epel/5/i386/epel-release-5-3.noarch.rpm’
…
su -c ‘yum install foo’