In this post I am going to explain how to enable GUI root access on Debian 8. Instructions for Debian 9 a similar and can be found here. At this point I should warn you that using the root account is dangerous as you can ruin your whole system.  Try to follow this guide exactly.

1. First open a terminal and type su then your root password that you created when installing your Debian 8.
2. Install Leafpad text editor which allows you to edit text files. Type: “apt-get install leafpad”
3. Stay in root terminal and type “leafpad /etc/gdm3/daemon.conf”. This command opens the file “daemon.conf” in leafpad. Under security type “AllowRoot=true”. So your security section in the file should look like this:[security]
   AllowRoot=trueOnce it looks like this save the file then exit the window.
4. Stay in root terminal and type “leafpad /etc/pam.d/gdm-password”. This command opens the file “gdm-password” in leafpad. Within this file you have comment out the line containing “auth required pam_succeed_if.so user != root quiet_success” so that it looks like this
   #auth required pam_succeed_if.so user != root quiet_successSave the file and exit.
5. Now you should be able to login as root in you GUI Debian 8.

Check out this post, if you are looking for instructions on how to enable GUI root access on Debian 9 – KDE5 Plasma.