If you've misplaced or simply forgotten the administrator password on your Mac, you won't be able to perform necessary software updates, change certain settings or install new software. You may even be unable to log in to your computer. However, there are ways you can bypass or reset the administrator password on your Mac and take back control.
Resetting the Administrator Password
Insert the Mac OS X Install Disk ( No. 1) that came with your computer (not Mac OS X Install Disk No. 2).
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Restart your computer and hold down the "C" key on your keyboard. This will ensure your Mac boots from the install CD.
Choose your language and accept the license terms, then select "Reset Password" from the Installer menu.
Pick your hard drive (probably named Macintosh HD) and choose the name of the administrator whose password should be reset.
Select a new password. Don't forget it.
Restart your computer and log in using the administrator password you just reset.
Add a password hint to help you remember your password.
For better security, whenever possible, choose strong passwords with numbers and symbols that are not common words found in the dictionary.
If you know the password of another administrative user, you can use it to reset other administrators' passwords.
You may not be able to reset the administrator password if the firmware is also password protected. In this case, you will have to reformat the entire hard drive, resulting in catastrophic data loss.