locked out of sudo while knowing my password

Question

I have one admin account and recently I have accidentally added myself to a single group (usermod -G without -a). So, I am not in the sudoers file anymore. However, root is not loginable by default on Ubuntu. Do I reset the password for root during the boot process?

Answer 1

No need to reset root password (well, technically, Ubuntu's root does not even have a password). Do this:

• Reboot your PC
• In Grub's OS selection screen, choose "Ubuntu xxxx - recovery mode"

• Now you have a console with root privileges. Add your user back to sudo group:

  usermod -a -G sudo youruser
  

  The shell might reply that it cannot do it because the file system in mounted in read-only. To remount your fs in read-write: 'mount -o remount,rw /'

• That will be enough for sudo. But its suggested you also re-add yourself to other default administrative groups. You can reboot, logon normally and use GUI:

Menu > Administration > Users and Groups > Advanced Settings > User Privileges or Account Type (Change...) > Administrative

• Or use this command:

  sudo usermod -a -G adm,cdrom,plugdev,fuse,lpadmin,sambashare youruser
  

Note: The 'sudo' group used to be the 'admin' group prior to Precise Pangolin. If you're on anything older, replace the group 'sudo' with the group 'admin' in the above commands.