This document provides instructions for enabling the EPEL (Extra Packages for Enterprise Linux) repository on RHEL (Red Hat Enterprise Linux) systems to gain access to additional packages. It describes downloading the EPEL rpm package, installing it to enable the repository, and checking that it is functioning properly by viewing available packages and installing a library from EPEL.

1. Habilitar repositorio EPEL RHEL | Moisés Araya
[1]
Habilitar repositorio EPEL Red Hat X64
EPEL (Extra Packages for Enterprise Linux) es un grupo de paquetes adicionales para Enterprise Linux,
estos puedes ser instalados en sistemas RHEL, CentOS y Scientific Linux, normalmente se utiliza para
instalar librerías que no están disponibles en los repositorios oficiales de CentOS o RHEL.
Procedimiento
Descargar repositorio
wget http://download.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm
--2015-10-06 10:19:28-- http://download.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm
Resolving download.fedoraproject.org... 5.175.150.50, 66.35.62.162, 67.203.2.67, ...
Connecting to download.fedoraproject.org|5.175.150.50|:80... connected.
HTTP request sent, awaiting response... 302 Found
Location: http://epel.gtdinternet.com/6/x86_64/epel-release-6-8.noarch.rpm [following]
--2015-10-06 10:19:29-- http://epel.gtdinternet.com/6/x86_64/epel-release-6-8.noarch.rpm
Resolving epel.gtdinternet.com... 190.196.123.25, 2800:160:1:46::2
Connecting to epel.gtdinternet.com|190.196.123.25|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 14540 (14K) [application/x-rpm]
Saving to: “epel-release-6-8.noarch.rpm.1”
100%[===========================================================================>] 14,540 --.-K/s in 0.001s
2015-10-06 10:19:29 (14.6 MB/s) - “epel-release-6-8.noarch.rpm.1” saved [14540/14540]
Instalar repositorio
[root@centos]# rpm -ivh epel-release-6-8.noarch.rpm
warning: epel-release-6-8.noarch.rpm: Header V3 RSA/SHA256 Signature, key ID 0608b895: NOKEY
Preparing... ########################################### [100%]
1:epel-release ########################################### [100%]
Verificar repositorio
yum repolist
Loaded plugins: refresh-packagekit, rhnplugin
This system is not registered with RHN.
RHN support will be disabled.
Error: Cannot retrieve metalink for repository: epel. Please verify its path and try again
[root@LCHGENGIR01 tmp]# yum --enablerepo=epel info zabbix
Loaded plugins: refresh-packagekit, rhnplugin
This system is not registered with RHN.
RHN support will be disabled.
Error: Cannot retrieve repository metadata (repomd.xml) for repository: epel. Please verify its path and try again

2. Habilitar repositorio EPEL RHEL | Moisés Araya
[2]
Solución:
[root@centos]# sed -i "s/mirrorlist=https/mirrorlist=http/" /etc/yum.repos.d/epel.repo
[root@centos]# yum check-update
Loaded plugins: refresh-packagekit, rhnplugin
This system is not registered with RHN.
RHN support will be disabled.
epel/metalink | 3.2 kB 00:00
epel | 4.3 kB 00:00
epel/primary_db
Verificar repositorio
[root@centos]# yum repolist |grep epel
This system is not registered with RHN.
RHN support will be disabled.
epel Extra Packages for Enterprise Linux 6 - x86_64 11,762
Consultar por un paquete instalado por EPEL
[root@centos]# yum --enablerepo=epel info nss-mdns
Loaded plugins: refresh-packagekit, rhnplugin
This system is not registered with RHN.
RHN support will be disabled.
Available Packages
Name : nss-mdns
Arch : i686
Version : 0.10
Release : 8.el6
Size : 22 k
Repo : epel
Summary : glibc plugin for .local name resolution
URL : http://0pointer.de/lennart/projects/nss-mdns/
License : LGPLv2+
Description: nss-mdns is a plugin for the GNU Name Service Switch (NSS) functionality of
: the GNU C Library (glibc) providing host name resolution via Multicast DNS
: (aka Zeroconf, aka Apple Rendezvous, aka Apple Bonjour), effectively allowing
: name resolution by common Unix/Linux programs in the ad-hoc mDNS domain .local.
:
: nss-mdns provides client functionality only, which means that you have to
: run a mDNS responder daemon separately from nss-mdns if you want to register
: the local host name via mDNS (e.g. Avahi).
Name : nss-mdns
Arch : x86_64
Version : 0.10
Release : 8.el6
Size : 22 k
Repo : epel
Summary : glibc plugin for .local name resolution
URL : http://0pointer.de/lennart/projects/nss-mdns/
License : LGPLv2+
Description: nss-mdns is a plugin for the GNU Name Service Switch (NSS) functionality of
: the GNU C Library (glibc) providing host name resolution via Multicast DNS
: (aka Zeroconf, aka Apple Rendezvous, aka Apple Bonjour), effectively allowing
: name resolution by common Unix/Linux programs in the ad-hoc mDNS domain .local.
:
: nss-mdns provides client functionality only, which means that you have to
: run a mDNS responder daemon separately from nss-mdns if you want to register
: the local host name via mDNS (e.g. Avahi).

3. Habilitar repositorio EPEL RHEL | Moisés Araya
[3]
Instalar Liberia
Habilitar el repositorio solo para instalar la librería necesaria.
[root@centos]# yum --enablerepo=epel install nss-mdns
Loaded plugins: refresh-packagekit, rhnplugin
This system is not registered with RHN.
RHN support will be disabled.
Setting up Install Process
Resolving Dependencies
--> Running transaction check
---> Package nss-mdns.x86_64 0:0.10-8.el6 set to be updated
--> Finished Dependency Resolution
Dependencies Resolved
=================================================================================================================
====
Package Arch Version Repository Size
=================================================================================================================
====
Installing:
nss-mdns x86_64 0.10-8.el6 epel 22
k
Transaction Summary
=================================================================================================================
====
Install 1 Package(s)
Upgrade 0 Package(s)
Total download size: 22 k
Installed size: 71 k
Is this ok [y/N]: y
Downloading Packages:
nss-mdns-0.10-8.el6.x86_64.rpm | 22 kB 00:00
warning: rpmts_HdrFromFdno: Header V3 RSA/SHA256 Signature, key ID 0608b895: NOKEY
epel/gpgkey | 3.2 kB 00:00
...
Importing GPG key 0x0608B895 "EPEL (6) <epel@fedoraproject.org>" from /etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL-6
Is this ok [y/N]: y
Running rpm_check_debug
Running Transaction Test
Transaction Test Succeeded
Running Transaction
Warning: RPMDB altered outside of yum.
glibc-2.12-1.7.el6.i686 has missing requires of libfreebl3.so
glibc-2.12-1.7.el6.i686 has missing requires of libfreebl3.so(NSSRAWHASH_3.12.3)
glibc-utils-2.12-1.7.el6.x86_64 has missing requires of libgd.so.2()(64bit)
Installing : nss-mdns-0.10-8.el6.x86_64 1/1
Installed:
nss-mdns.x86_64 0:0.10-8.el6
Fuentes:
https://community.hpcloud.com/article/centos-63-instance-giving-cannot-retrieve-metalink-repository-epel-error
http://www.tecmint.com/how-to-enable-epel-repository-for-rhel-centos-6-5/