do_action( 'admin_init' )
Fires as an admin screen or script is being initialized.
Note, this does not just run on user-facing admin screens. It runs on admin-ajax.php and admin-post.php as well.
This is roughly analogous to the more general ‘init’ hook, which fires earlier.
admin_init is triggered before any other hook when a user accesses the admin area.
This hook doesn’t provide any parameters, so it can only be used to callback a specified function.