Tuesday, 6 March 2012

How to reset lost user password on a Linux Machine

First you’ll want to make sure to choose the regular boot kernel that you use (typically just the default one), and then use the “e” key to choose to edit that boot option.

Now just hit the down arrow key over to the “kernel” option, and then use the “e” key to switch to edit mode for the kernel option.

Note: if the grub menu does not show up try hitting the Shift or the Space keys right after the bios screen.

You’ll want to remove the “ro quiet splash” part with the backspace key, and then add this onto the end:
rw init=/bin/bash
Press F10 or ctrl+x to boot with that option.

At this point the system should boot up very quickly to a command prompt.

Now you can use the passwd command to change the password.
passwd username
where username is the username you want to reset.
After changing your password, use the following commands to reboot your system. (The sync command makes sure to write out data to the disk before rebooting)
reboot –f
I found that the –f parameter was necessary to get the reboot command to work for some reason. You could always hardware reset instead, but make sure to use the sync command first.

NOTE for VMWare users:

Probably you wont ever see the boot menu on a VM because it will boot to fast, to work around this you can set up the vm to delay the bios for a few seconds:
bios.bootDelay = "15000"
This causes the bios to delay for 15 seconds so you can press keys, you can set it in the VM .vmx file or using vSphere under the vm settings, on the options tab, boot options.

Then just start the VM and press esc on the grub loading message and follow the steps described above.

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