repo creation and epel repo creation

what is repository

A software repository, or “repo” for short, is a storage location for software packages. Often a table of contents is stored, as well as metadata. Repositories group packages.

what is sudo?

a sudo is having full execution permission as root user has. That means the user specifically having sudo means that user can do what ever root can do almost all services.

[bala@balatest ~]$ sudo mount /dev/sr0 /mnt

We trust you have received the usual lecture from the local System
Administrator. It usually boils down to these three things:

    #1) Respect the privacy of others.
    #2) Think before you type.
    #3) With great power comes great responsibility.

[sudo] password for bala:
mount: /mnt: WARNING: device write-protected, mounted read-only.

[bala@balatest ~]$ sudo cp /mnt/media.repo /etc/yum.repos.d/rhel8.repo
[root@balatest bala]# vi /etc/yum.repos.d/rhel8.repo

[InstallMedia-BaseOS]
name=Red Hat Enterprise Linux 8 - BaseOS
metadata_expire=-1
gpgcheck=1
enabled=1
baseurl=file:///mnt/BaseOS/ gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release
[InstallMedia-AppStream]
name=Red Hat Enterprise Linux 8 - AppStream
metadata_expire=-1
gpgcheck=1
enabled=1
baseurl=file:///mnt/AppStream/
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release

EPEL -Extra Packages for Enterprise Linux

is an open-source and free community-based repository project from Fedora team which provides 100% high-quality add-on software packages for Linux distribution including RHEL-Red Hat Enterprise Linux8

[bala@balatest ~]$ su
Password:

[root@balatest bala]# dnf install https://dl.fedoraproject.org/pub/epel/epel-release-latest-8.noarch.rpm

Updating Subscription Management repositories.
Unable to read consumer identity
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
Red Hat Enterprise Linux 8 - BaseOS              21 MB/s | 2.2 MB     00:00 
Red Hat Enterprise Linux 8 - AppStream           31 MB/s | 5.6 MB     00:00 
Last metadata expiration check: 0:00:01 ago on Wed 12 Feb 2020 04:30:26 PM IST.
epel-release-latest-8.noarch.rpm                 13 kB/s |  21 kB     00:01 
Dependencies resolved.
================================================================================
 Package              Architecture   Version         Repository            Size
================================================================================
Installing:
 epel-release         noarch         8-7.el8         @commandline          21 k

Transaction Summary
================================================================================
Install  1 Package

Total size: 21 k
Installed size: 30 k
Is this ok [y/N]: y
Downloading Packages:
Running transaction check
Transaction check succeeded.
Running transaction test
Transaction test succeeded.
Running transaction
  Preparing        :                                                        1/1
  Installing       : epel-release-8-7.el8.noarch                            1/1
  Running scriptlet: epel-release-8-7.el8.noarch                            1/1
  Verifying        : epel-release-8-7.el8.noarch                            1/1
Installed products updated.

Installed:
  epel-release-8-7.el8.noarch                                                 

Complete!

[root@balatest bala]# sudo dnf repolist -v

Loaded plugins: builddep, changelog, config-manager, copr, debug, debuginfo-install, download, generate_completion_cache, needs-restarting, playground, product-id, repoclosure, repodiff, repograph, repomanage, reposync, subscription-manager, uploadprofile
Updating Subscription Management repositories.
Unable to read consumer identity
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
DNF version: 4.2.7
cachedir: /var/cache/dnf
repo: downloading from remote: epel
Extra Packages for Enterprise Linux 8 - x86_64  1.4 MB/s | 5.6 MB     00:04 
epel: using metadata from Mon 10 Feb 2020 05:40:19 AM IST.
repo: using cache for: InstallMedia-BaseOS
InstallMedia-BaseOS: using metadata from Tue 15 Oct 2019 06:57:47 PM IST.
repo: using cache for: InstallMedia-AppStream
InstallMedia-AppStream: using metadata from Tue 15 Oct 2019 06:57:36 PM IST.
Last metadata expiration check: 0:00:03 ago on Wed 12 Feb 2020 04:33:08 PM IST.
Completion plugin: Generating completion cache...

Repo-id      : InstallMedia-AppStream
Repo-name    : Red Hat Enterprise Linux 8 - AppStream
Repo-revision: 1571146056
Repo-updated : Tue 15 Oct 2019 06:57:36 PM IST
Repo-pkgs    : 4,820
Repo-size    : 5.6 G
Repo-baseurl : file:///mnt/AppStream/
Repo-expire  : Never (last: Wed 12 Feb 2020 04:30:37 PM IST)
Repo-filename: /etc/yum.repos.d/rhel8.repo

Repo-id      : InstallMedia-BaseOS
Repo-name    : Red Hat Enterprise Linux 8 - BaseOS
Repo-revision: 1571146067
Repo-updated : Tue 15 Oct 2019 06:57:47 PM IST
Repo-pkgs    : 1,661
Repo-size    : 961 M
Repo-baseurl : file:///mnt/BaseOS/
Repo-expire  : Never (last: Wed 12 Feb 2020 04:30:37 PM IST)
Repo-filename: /etc/yum.repos.d/rhel8.repo

Repo-id      : epel
Repo-name    : Extra Packages for Enterprise Linux 8 - x86_64
Repo-revision: 1581293287
Repo-updated : Mon 10 Feb 2020 05:40:19 AM IST
Repo-pkgs    : 4,712
Repo-size    : 5.4 G
Repo-metalink: https://mirrors.fedoraproject.org/metalink?repo=epel-8&arch=x86_6
4&infra=$infra&content=$contentdir
  Updated    : Wed 12 Feb 2020 04:33:08 PM IST
Repo-baseurl : http://mirrors.piconets.webwerks.in/fedora-mirror/epel/8/Everythi
ng/x86_64/
             : (58 more)
Repo-expire  : 172,800 second(s) (last: Wed 12 Feb 2020 04:33:08 PM IST)
Repo-filename: /etc/yum.repos.d/epel.repo
Total packages: 11,193

DNF or Dandified YUM is the next-generation version of the Yellowdog Updater, Modified, a package manager for .rpm-based distributions.
DNF was introduced in Fedora 18 in 2013, it has been the default package manager since Fedora 22 in 2015 and Red Hat Enterprise Linux 8.