Reset lost root password and more using Knoppix (Linux live CD)

Whew….It’s been a while since I’ve weblogged something. Grades have gone up and down, exams have come and go (and they’re still coming btw).

What happened was I needed to replicate a setup (my thesis actually) on an all-in-one-PC (very similar to this one though with only 512 MB of RAM). I installed Arch Linux (for reasons I hope I’ll be able to weblog about sometime soon) and I forgot the root password after I installed it. It was a careless move and I should have backed the root password up after setting it (by sending an e-mail to myself for example).
Here’s how I reset the root password:
Firstly, there are a number of different ways to do this, but what I’ll be using is a live Linux CD. You can select a number of them here, but I personally prefer Knoppix, which I also think is the best all-around Linux live CD. I’m currently using the 5.1 version of Knoppix, though I think this will work even if you use the 3.x versions.
Secondly, we proceed to the resetting proper.
1) reboot the PC and boot from the Knoppix CD.
2) Usually, the default language of Knoppix is US-English, but if you boot it and it doesn’t appear to be so, enter this at the boot prompt:

knoppix lang=us

then hit enter
3) you can actually not boot a GUI (such as KDE or fluxbox) but in case you do, this will still work nonetheless.
4) open a terminal/console and type

su

so you can get root access
5) create a dummy directory which we’ll use to mount the partition where you installed the Linux OS which you want to reset the password to. In this case I enter

 mkdir testdir

6) enter

 mount /dev/hdaX testdir

if your hard drive was scanned as an IDE hard drive or

 mount /dev/sdaX testdir

if it was scanned as a SCSI drive. X represents the partition number of the drive where the root password, and hence, the

 /root

is installed. This assumes that sdaX or hdaX includes the file you want to edit, in this case the file which contains the root password you want to remove/change.

7) change to the

/etc

directory by entering

 cd testdir/etc

8 ) use a text editor such as

vi

or

vim

to open the

shadow

file.
9) Once you open the file

shadow

go to the line entry with

root

in it. It should look something like this

root:dsfDSDF!s:12581:0:99999:7:::

10) Delete everything in between the first and second colons, so that the entry will look like this

root::12581:0:99999:7:::

11) save and exit your editor
12) change to your home directory, for example enter

 cd

13) unmount the partition:

umount testdir

14) enter

reboot

to reboot the system and remove the Knoppix live CD.
Now you can login to your system as root without any password to begin with! Make sure to do

passwd

asap to change the root password!

Using the same principle, you can verily see how easy it is to edit other system files when something happens to your machine, be it a Linux or a Windows machine. You can edit (in Linux) your resolv.conf, fstab, and a lot more using this technique. That’s why I always keep a live Linux CD around! (^)__(^)