There are two ways to add a repository to YUM.

• Add a .repo file to the /etc/yum.repos.d/ directory (preferred)
• Add a [repository] block to /etc/yum.conf

Let's say you want to add the EPEL repository. Typically, this would be done by issuing the following command.

yum install epel-release

If using an Amazon EC2 instance, you might need to go with this command.

sudo amazon-linux-extras install epel

This command will create the epel.repo file in the /etc/yum.repos.d directory.

~]$ ll /etc/yum.repos.d/
-rw-r--r--. 1 root root 1664 Apr  7  2020 CentOS-Base.repo
-rw-r--r--. 1 root root 1309 Apr  7  2020 CentOS-CR.repo
-rw-r--r--. 1 root root  649 Apr  7  2020 CentOS-Debuginfo.repo
-rw-r--r--. 1 root root  314 Apr  7  2020 CentOS-fasttrack.repo
-rw-r--r--. 1 root root  630 Apr  7  2020 CentOS-Media.repo
-rw-r--r--. 1 root root 1331 Apr  7  2020 CentOS-Sources.repo
-rw-r--r--. 1 root root 7577 Apr  7  2020 CentOS-Vault.repo
-rw-r--r--. 1 root root  616 Apr  7  2020 CentOS-x86_64-kernel.repo
-rw-r--r--  1 root root 1050 Oct 31  2020 epel.repo
-rw-r--r--  1 root root 1149 Oct 31  2020 epel-testing.repo

Alternatively, you could manually create a repo file, such as foo.repo.

touch /etc/yum.repos.d/foo.repo

And then add something like this to the repo file.

[foo]
name=foo repository
baseurl=http://www.example.com/foo
enabled=1
gpgcheck=0