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Recover/Reset root password under linux(Ubuntu/RHEL/CentOS)

Postby chandranjoy » Wed Jan 05, 2011 3:39 pm

How-To: Recover root password under linux(Ubuntu) with single user mode:

It happens sometime that you can't remember root password. On Linux, recovering 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 and finally how to change root password.

During normal usage, a Linux OS runs under runlevels between 2 and 5 which corresponds to various multi-user modes. Booting Linux under runlevel 1 will allow one to enter into a specific mode, single user mode. Under such a level, you directly get a root prompt. From there, changing root password is a piece of cake.

1. Entering runlevel 1
Some Linux distribution, such as Ubuntu for instance, offer a specific boot menu entry where it is stated "Recovery Mode" or "Single-User Mode". If this is your case, selecting this menu entry will boot your machine into single user mode, you can carry on with the next part. If not, you might want to read this part.

Using GRUB, you can manually edit the proposed menu entry at boot time. To do so, when GRUB is presenting the menu list (you might need to press ESC first), follow those instructions:
* use the arrows to select the boot entry you want to modify.
* press e to edit the entry
* use the arrows to go to kernel line
* press e to edit this entry
* at the end of the line add the word single
* press ESC to go back to the parent menu
* press b to boot this kernel


The kernel should be booting as usual (except for the graphical splash screen you might be used to), and you will finally get a root prompt (sh#).

Here we are, we have gained root access to the filesystem, let's finally change the password.

2. Changing root password
As root, changing password does not ask for your old password, therefore running the command:
# passwd


will prompt you for your new password and will ask you to confirm it to make sure there is no typo.

That's it, you can now reboot your box and gain root access again.


For Debian/Ubuntu:

If you forgot you password for your ubuntu system you can recover using the following steps

Turn your computer on.

Press ESC at the grub prompt.

Press e for edit.

Highlight the line that begins kernel ………, press e

Go to the very end of the line, add rw init=/bin/bash

press enter, then press b to boot your system.

Your system will boot up to a passwordless root shell.

Type in passwd root

Set your password.

Type in reboot


Cheers :)
chandranjoy
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