Reset the root password in Debian or Ubuntu

In order to boot into the recovery mode on Debian or Ubuntu, hold down SHIFT key after powering on your Linux machine. You will then be presented with GRUB menu. Select “recovery menu” option by pressing down arrow key. Do not press ENTER at this point, but rather press “e” key to enter edit mode.

You will see “GRUB” edit screen where you can edit GRUB boot parameters. Move your cursor to the line starting with “linux /boot/vmlinuz-…….”, and go to the end of that line. Append “init /bin/bash” right there, as shown below.

Then press Ctrl+X to proceed. After all subsequent booting sequence is over, you will finally get a root prompt.

In the recovery mode, the root partition is mounted as read-only by default, and so you cannot change the root password as is. In order to be able to reset the root password, you need to re-mount the root partition as read-write.

First, find out what the root partition of your system is, by using “fdisk -l” command.

As shown in the screenshot above, the partition marked with “*” under “Boot” column is the root partition of your system (e.g., /dev/sda1).

Remount the root partition as read-write, and finally reset the password, using passwd command.
$ mount -o remount,rw /dev/sda1 /
$ passwd