When you install software packages on a CentOS Linux system with yum, the utility will query repositories, which are sources for software packages, to find the package you wish to install. There are some packages, such as Iperf and fail2ban, which aren't in the default repositories for CentOS, but which can be found in the Extra Packages for Enterprise Linux (EPEL) repository. EPEL is a "community approved" repository, which is listed on the CentOS wiki under Available Repositories for Linux, which notes that though community repositories are not associated with the CentOS project, that "These repositories are frequently recommended by the community, are usually well maintained, and provide a substantial number of additional packages to CentOS." The wiki also notes:
Extra Packages for Enterprise Linux (EPEL) - (See http://fedoraproject.org/wiki/EPEL) provides rebuilds of Fedora packages for EL5, EL6 and EL7. Packages should not replace base, although there have been issues around point releases in the past. You can install EPEL by running yum install epel-release. The epel-release package is included in the CentOS Extras repository that is enabled by default. Support available on Freenode in #epel, on mailing lists, and its issue tracker.
If the epel-release package is already installed, an RPM query will show it is present.
# rpm -qi epel-release Name : epel-release Version : 7 Release : 5 Architecture: noarch Install Date: Sun 04 Jan 2015 12:48:24 PM EST Group : System Environment/Base Size : 24914 License : GPLv2 Signature : RSA/SHA256, Tue 25 Nov 2014 01:06:15 PM EST, Key ID 6a2faea2352c64e5 Source RPM : epel-release-7-5.src.rpm Build Date : Tue 25 Nov 2014 11:26:18 AM EST Build Host : buildvm-21.phx2.fedoraproject.org Relocations : (not relocatable) Packager : Fedora Project Vendor : Fedora Project URL : http://download.fedoraproject.org/pub/epel Summary : Extra Packages for Enterprise Linux repository configuration Description : This package contains the Extra Packages for Enterprise Linux (EPEL) repository GPG key as well as configuration for yum.
If the system is already configured to use that repository, you should see
it listed if you issue the yum repolist command.
$ yum repolist Loaded plugins: fastestmirror, langpacks Determining fastest mirrors * base: mirror.cs.pitt.edu * epel: mirror.us.leaseweb.net * extras: mirror.lug.udel.edu * updates: centos.mirror.lstn.net repo id repo name status base/7/x86_64 CentOS-7 - Base 9,007 epel/x86_64 Extra Packages for Enterprise Linux 7 - x86_64 9,710 extras/7/x86_64 CentOS-7 - Extras 264 updates/7/x86_64 CentOS-7 - Updates 1,213 repolist: 20,194 $
If EPEL support isn't installed, issue the command yum install
epel-release to install it. Once it is installed, you will see the
repository listed in /etc/yum.repos.d.
$ ls -l /etc/yum.repos.d total 32 -rw-r--r--. 1 root root 1664 Mar 31 2015 CentOS-Base.repo -rw-r--r--. 1 root root 1309 Mar 31 2015 CentOS-CR.repo -rw-r--r--. 1 root root 649 Mar 31 2015 CentOS-Debuginfo.repo -rw-r--r--. 1 root root 290 Mar 31 2015 CentOS-fasttrack.repo -rw-r--r--. 1 root root 1331 Mar 31 2015 CentOS-Sources.repo -rw-r--r--. 1 root root 1002 Mar 31 2015 CentOS-Vault.repo -rw-r--r--. 1 root root 957 Nov 25 2014 epel.repo -rw-r--r--. 1 root root 1056 Nov 25 2014 epel-testing.repo