The Linux repositories are a fundamental part in the stability and smooth operation of systems and applications, they are responsible for keeping up to date with the latest updates required for our system and applications.
A Linux repository is a storage location from which your system retrieves and installs updates and applications from the operating system. Each repository is a set of software hosted on a remote server in order to be used to install and update software packages on Linux systems.

YUM is a command-line package management utility for Linux systems based on RPM and with GNU General Public License. Yum is useful for RPMs that contain dependencies. Yum searches all dependencies of any RPM in all available repositories.

The list below contains the main yum repositories (RPMFusin, EPEL, REMI, ELRepo, Webtatic) for RHEL-based systems with installation links, which we need to keep our system updated with the latest packages. These repositories have the majority of the RPM needed for the servers.

RPMFusin repository
The RPM Fusion repository provides packages that are not sent with Fedora or Red Hat. You can add the RPMFusion yum repository by running the following commands depending on the version of the system operating system.

CentOS/RHEL 7
sudo yum localinstall --nogpgcheck https://download1.rpmfusion.org/free/el/rpmfusion-free-release-7.noarch.rpm
sudo yum localinstall --nogpgcheck https://download1.rpmfusion.org/nonfree/el/rpmfusion-nonfree-release-7.noarch.rpm

CentOS/RHEL 6
sudo yum localinstall --nogpgcheck https://download1.rpmfusion.org/free/el/rpmfusion-free-release-6.noarch.rpm
sudo yum localinstall --nogpgcheck https://download1.rpmfusion.org/nonfree/el/rpmfusion-nonfree-release-6.noarch.rpm

Fedora 28/27/26/25/24
sudo dnf install https://download1.rpmfusion.org/free/fedora/rpmfusion-free-release-$(rpm -E %fedora).noarch.rpm
sudo dnf install https://download1.rpmfusion.org/nonfree/fedora/rpmfusion-nonfree-release-$(rpm -E %fedora).noarch.rpm

EPEL Repository
Additional packages for Enterprise Linux (EPEL) is a group that keeps the latest packages in its repository. It also contains the necessary additional packages for Red Hat Enterprise Linux (RHEL), CentOS, Scientific Linux (SL) and Oracle Linux (OL).

We can use the following commands to install the EPEL yum repository on your CentOS / RHEL 7/6/5 systems.

CentOS/RHEL 7
sudo yum localinstall --nogpgcheck http://dl.fedoraproject.org/pub/epel/7/x86_64/Packages/e/epel-release-7-11.noarch.rpm

CentOS/RHEL 6
sudo yum localinstall --nogpgcheck http://dl.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm

REMI Repository
REMI is also a useful yum repository contains updated packages for Enterprise Linux systems. Use the following commands to install REMI yum repository on your CentOS/RHEL 7/6 and Fedora 28/27/26/25/24 systems.

CentOS/RHEL 7
sudo yum localinstall --nogpgcheck http://rpms.famillecollet.com/enterprise/remi-release-7.rpm

CentOS/RHEL 6
sudo yum localinstall --nogpgcheck http://rpms.famillecollet.com/enterprise/remi-release-6.rpm

Fedora 28/27/26/25/24
sudo dnf install http://rpms.famillecollet.com/fedora/remi-release-$(rpm -E %fedora).rpm

ELRepo Repository
ELRepo is an RPM repository for Enterprise Linux packages. It supports Red Hat Enterprise Linux (RHEL) and its derivatives like CentOS, Scientific Linux etc. This Project focuses on hardware related packages to enhance your experience with Enterprise Linux. This includes filesystem drivers, graphics drivers, network drivers, sound drivers, webcam and video drivers.

CentOS/RHEL 7
sudo rpm --import https://www.elrepo.org/RPM-GPG-KEY-elrepo.org
sudo rpm -Uvh http://www.elrepo.org/elrepo-release-7.0-3.el7.elrepo.noarch.rpm

CentOS/RHEL 6
sudo rpm --import https://www.elrepo.org/RPM-GPG-KEY-elrepo.org
sudo rpm -Uvh http://www.elrepo.org/elrepo-release-6-8.el6.elrepo.noarch.rpm

Webtatic Repository
Webtatic is a yum repository generally deals with the web hosting related packages, which is not included with CentOS/RHEL repositories. Execute one of the following commands to install REMI yum repository on your CentOS/RHEL 7/6/5 systems.

CentOS/RHEL 7
sudo yum localinstall --nogpgcheck http://repo.webtatic.com/yum/el7/webtatic-release.rpm

CentOS/RHEL 6
sudo yum localinstall --nogpgcheck http://repo.webtatic.com/yum/el6/latest.rpm

CentOS/RHEL 5
sudo yum localinstall --nogpgcheck http://repo.webtatic.com/yum/el5/latest.rpm