how to enable repo with yum-config-manager --enable<repo> - yum

Question

During the try to install yum-utils, I ran into the problem that there seems to be no enabled repos. How can I enable yum-config-manager, when I seem to need him to do so.
[root#spectrumscale ~]# yum install yum-utils
Failed to set locale, defaulting to C
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
There are no enabled repos.
Run "yum repolist all" to see the repos you have.
You can enable repos with yum-config-manager --enable <repo>

Answer 1

To install specific package from specific repo you can use
yum install --enablerepo=name-of-repo name-of-package
Say there can be conflict between version, consider example of installing mariadb 5.5.66, in my case I got 2 repo mariadb-5 and mariadb-10, suppose if I wish to install from mariadb-5 repo then I use
yum install --disablerepo=mariadb-10 --enablerepo=mariadb-5 MariaDB-server MariaDB-client
To enable enable specific repo, you can use
yum-config-manager --enable name-of-repo
Here is example on Centos 7.7
[root#localhost server-setup]# cat /etc/redhat-release
CentOS Linux release 7.7.1908 (Core)
[root#localhost server-setup]# yum repolist
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
* base: mirrors.piconets.webwerks.in
* epel: mirror.poliwangi.ac.id
* extras: mirrors.piconets.webwerks.in
* remi-safe: mirror.innosol.asia
* updates: mirrors.piconets.webwerks.in
repo id repo name status
CodeIT/x86_64 CodeIT repo 369
base/7/x86_64 CentOS-7 - Base 10,097
epel/x86_64 Extra Packages for Enterprise Linux 7 - x86_64 13,453
extras/7/x86_64 CentOS-7 - Extras 305
ius/x86_64 IUS for Enterprise Linux 7 - x86_64 641
mariadb-10 MariaDB 94
mariadb-5 MariaDB 39
remi-safe Safe Remi's RPM repository for Enterprise Linux 7 - x86_64 3,621
updates/7/x86_64 CentOS-7 - Updates 711
repolist: 29,330
To Disable
[root#localhost server-setup]# yum-config-manager --disable mariadb-5
After Disabling
[root#localhost server-setup]# yum repolist
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
* base: mirrors.piconets.webwerks.in
* epel: mirror.poliwangi.ac.id
* extras: mirrors.piconets.webwerks.in
* remi-safe: mirror.innosol.asia
* updates: mirrors.piconets.webwerks.in
repo id repo name status
CodeIT/x86_64 CodeIT repo 369
base/7/x86_64 CentOS-7 - Base 10,097
epel/x86_64 Extra Packages for Enterprise Linux 7 - x86_64 13,453
extras/7/x86_64 CentOS-7 - Extras 305
ius/x86_64 IUS for Enterprise Linux 7 - x86_64 641
mariadb-10 MariaDB 94
remi-safe Safe Remi's RPM repository for Enterprise Linux 7 - x86_64 3,621
updates/7/x86_64 CentOS-7 - Updates 711
repolist: 29,291
What it actually does ???
I got MariaDB.repo file at /etc/yum.repos.d/, when you use --enable <repo-name> or --disable <repo-name>, it will change the value of enabled = to 0 or 1, based on this, yum repolist will show you repositories.
[root#localhost server-setup]# cat /etc/yum.repos.d/MariaDB.repo
[mariadb-10]
name = MariaDB
baseurl = http://yum.mariadb.org/10.4.10/centos7-amd64
gpgkey=https://yum.mariadb.org/RPM-GPG-KEY-MariaDB
gpgcheck=1
[mariadb-5]
name = MariaDB
baseurl = http://yum.mariadb.org/5.5.66/centos7-amd64
gpgkey=https://yum.mariadb.org/RPM-GPG-KEY-MariaDB
gpgcheck=1
enabled = 1