CentOS 7

cd /usr/src
rpm -Uvh https://dl.fedoraproject.org/pub/epel/7/x86_64/Packages/e/epel-release-7-11.noarch.rpm

CentOS 6

rpm -Uvh https://dl.fedoraproject.org/pub/epel/6/x86_64/Packages/e/epel-release-6-8.noarch.rpm