I can login to my Ubuntu 16.04 server no problem with my usual password but when I try to give admin privleges through terminal sudo -s, the password doesn't work. Strange because it always worked. I get the following error:
"Username is not in the sudoers file etc ...."
I did a search and it seems like a common error and recommend that go into recovery mode from grub.
But then there is no Recovery Menu that shows up (DOS window) from the grub recovery mode.