I was able to to do it on 17.04, but i guess the display manager has changed
I know it is not recommended. But it eases a lot of things for me.
This link points it out for Debian, but instead of daemon.conf
just edit custom.conf
. Everything else is the same.
In a nutshell, first run
sudo vim /etc/gdm3/custom.conf
Under [security]
type AllowRoot=true
so that it looks like
[security]
AllowRoot=true
Save and exit. Then run
sudo vim /etc/pam.d/gdm-password
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_success
Save the file and exit and reboot.
gdm3
.