Add User to Sudoers on CentOS

You can do this in 2 methods- however, IMHO method-2 usually works great for me.

Method-1

Step 1: Verify the Wheel Group is Enabled

Your CentOS 7 installation may or may not have the wheel group enabled. Open the configuration file by entering the command:

visudo

Scroll through the configuration file until you see the following entry:

## Allows people in group wheel to run all commands
# %wheel        ALL=(ALL)       ALL

If the second line begins with the # sign, it has been disabled and marked as a comment. Just delete the # sign at the beginning of the second line so it looks like the following:

%wheel        ALL=(ALL)       ALL

Then save the file and exit the editor.

Note: If this line didn’t start with a # sign, you don’t need to make any changes. The wheel group is already enabled, and you can close the editor.

Step 2: Add User to Group

To add a user to the wheel group, use the command:

usermod –aG wheel UserName

As usual, replace UserName with the name of the user receiving sudo privileges.

Step: 3 Switch to the Sudo User

Switch to the new (or newly-elevated) user account with the su (substitute user) command:

su - UserName

Enter the password if prompted. The terminal prompt should change to include the UserName. Enter the following command to list the contents of the /root directory:

sudo ls -la /root

The terminal should request the password for UserName. Enter it, and you should see a display of the list of directories. Since listing the contents of /root requires sudo privileges, this works as a quick way to prove that UserName can use the sudo command.

Method-2

Alternative: Add User to Sudoers Configuration File

If there’s a problem with the wheel group, or administrative policy prevents you from creating or modifying groups, you can add a user directly to the sudoers configuration file to grant sudo privileges.

Step 1: Open the Sudoers File in an Editor

In the terminal, run the following command:

nano /etc/sudoers 

Step 2: Add the New User to file

Scroll down to find the following section:

## Allow root to run any commands anywhere

root ALL=(ALL) ALL

Right after this entry, add the following text:

UserName ALL=(ALL) ALL

Replace UserName with the username you created in Step 2. This section should look like the following:

## Allow root to run any commands anywhere

root ALL=(ALL) ALL
UserName ALL=(ALL) ALL

Save the file and exit.

Step 3: Test Sudo Privileges for the User Account

Switch user accounts with the su (substitute user) command:

su - UserName

Enter the password for the account, if prompted. The terminal prompt should change to include UserName. List the contents of the /root directory:

sudo ls - la /root

Enter the password for this user when prompted. The terminal should display a list of all the directories in the /root directory.

Src:
https://phoenixnap.com/kb/how-to-create-add-sudo-user-centos