Reset lost root password on Ubuntu 18.04 Bionic Beaver Linux

Boot Into GRUB menu

The first step is to reboot into the GRUB menu. If Ubuntu 18.04 Bionic Beaver is the only operating system installed you need to keep pressing SHIFT for the GRUB menu to show up.

Edit Grub Menu

Using arrows select the Ubuntu menu or the menu you use to boot your system and hit the e key. This will allow you to edit the menu:

Navigate down with the arrow-down key until you can see a line ending with:

ro quiet splash $vt_handoff

Using your keyboard replace the following keywords.

FROM: r o quiet splash $vt_handoff
TO: rw init=/bin/bash

Once you have made the change press F10 or CTRL + x to perform boot into a single mode.

Reset password

Confirm that your system partition is mounted as read/write (rw):

# mount | grep -w /

If all good, reset your root password with the passwd command:

# passwd

Reboot

Your root password is now reset. Reboot your system:

# exec /sbin/init