It happens sometime that you can’t remember root password. On Linux, resetting root password can be done by booting Linux under a specific mode: single user mode. This tutorial will show how to boot Linux in single user mode when using GRUB or LILO and finally how to change forgotten root password.

If your boot loader is GRUB, follow the procedure below to reset your lost root password:

1. Select the kernel.
2. Press the e key to edit the entry.
3. Select second line (the line starting with the word kernel).
4. Press the e key to edit kernel entry so that you can append single user mode.
5. Append the letter S (or word Single) to the end of the (kernel) line.
6. Press ENTER key.
7. Now press the b key to boot the Linux kernel into single user mode.
8. At prompt type passwd command to reset password.

You need to mount at least / and other partitions:
# mount -t proc proc /proc
# mount -o remount,rw /

Change the root password, enter:
# passwd

Finally reboot system:
# sync
# reboot

If your boot loader is LILO:
At LILO boot loader type linux single and press [ENTER] key:
Boot: linux single

When you get the # prompt you will need to type passwd root to reset password:
# passwd

Reboot system:
# sync
# reboot

If you need to reset forgotten Windows admin/user password, please refer to this software: Reset Windows Password.