We all face the issue of spam registrations on 
our websites. Many of the times, we want to disable user registrations on the 
website. This post details how the same can be done in Drupal. Drupal allows the 
following different settings for user registrations -
- Only site administrators can create new 
	user accounts.
- Visitors can create accounts and no 
	administrator approval is required.
- Visitors can create accounts but 
	administrator approval is required.
By default, Drupal comes with the setting 
“Visitors can create accounts and no administrator approval is required.” so 
that users can register and are auto approved. To disable user registrations, we 
need to perform the following steps (I take the site example as http://www.yoursite.com)
In case, you are more interested to make this 
change from Database level, you can use the following query on your database:
UPDATE 
variable SET 'value' =
‘s:1:”0?;' 
WHERE 'name' =
‘user_register';