yum install realmd
realm discover –verbose example.com
That will tell you what software you need to install (samba-common doesn’t show up, but it will if you try to join a domain and it’s not installed).
yum install sssd oddjob oddjob-mkhomedir adcli samba-common
realm join –client-software=sssd example.com -U mydomainadmin
That should prompt for a password, and if successful, absolutely nothing will be displayed on STDOUT.
To test if you have successfully joined the domain, use
getent passwd EXAMPLE\\mydomainuser
and you should get a long passwd line.

Now, if you want to only allow certain users to log in, you can run the next two commands:
realm deny –all
realm permit [email protected]