Resetting / By passing OS X login password

Resetting / By passing OS X login password
1. Reboot
2. Hold apple + s down after you hear the chime.
3. When you get text prompt enter in these terminal commands to create a brand new admin account (hitting return after each line):
* mount -uw /
* rm /var/db/.AppleSetupDone
* shutdown -h now
4. After rebooting you should have a brand new admin account. When you login as the new admin you can simply delete the old one and you’re good to go again!


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If the Mac is in Read only mode:
Resetting PRAM and NVRAM
1. Shut down the computer.
2. Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in step 4.
3. Turn on the computer.
4. Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
5. Hold the keys down until the computer restarts and you hear the startup sound for the second time.
6. Release the keys.

Ref: http://illshare.wordpress.com/2008/06/01/how-to-resset-administrator-password-mac-os-x/