Map domain to subdomain

Have you spoken to your hosts about this?

No, I have a dedicated server and I can edit all files or DNS records

EDIT: When i said “all links i can click” i mean that the src tag even if i put “./about.php” render as “https://site.com/about.php” instead of “https://beta.site.com/about.php”
So i thought it was a WP configuration

Where did you install WordPress on this domain?

I have a folder /var/www/site/ where wordpress is located that points to https://site.com

Where did you install WordPress on this domain? In the root of site.com?

Yes in the root

Then you really need to look at Moving_WordPress.

Ok thanks for the link, but let me ask one more question before i continue, will this help me to Move WordPress or to Copy it ?
Because I need to access the Same WordPress content with my subdomain or domain like if it was the same.

I read many people who wanted to move indeed their installations, but I don’t want to move it, I just want to make a subdomain alias so that when I post an article via https://beta.site.com/wp-admin/post-new.php it works the same as if I was on https://site.com/wp-admin/post-new.php

Do you want 1 or 2 sites?

Just one, i just want an alias (another URL) for same website

You can only use one domain name per install, so the best you will be able to do is re-direct all calls for https://beta.site.com/foobar to https://site.com/wp-admin/foobar via .htaccess.

okay so this will work with htaccess ?
And do you know how to do it ?

Try googling on “.htaccess redirect”. And bear in mind that the final urls will always show https://site.com.foobar

I am googling right now and i will try some solutions, thanks
Also i think i will always encounter a problem when i try to log in via https://beta.site.com because wp-login.php redirects me to https://site.com instead of https://beta.site.com