How to Change a Forgotten iMac Passwordby Elle Smith ; Updated February 10, 2017
Setting a password on an iMac computer is important to protect the computer's contents from unauthorized access. When setting up an iMac computer, a master password can be assigned to the iMac administrator account, and sub-user accounts can also be password-protected. If sub-user passwords are forgotten, they are easily changed; but changing the iMac administrator's account takes a bit more work.
Boot up the computer and log in to the administrator's user account.
From the Apple menu, select "System Preferences."
When the System preferences window opens, look in the "System" pane, and choose "Accounts."
Click on the lock icon if it is locked, and enter the original iMac administrator's password.
In the Account Pane, click on the user account of the password you wish to change. In Mac OS X v10.3 and v10.4, click the "Reset Password" button. In Mac OS X v10.5 and later, click the "Change Password" button.
iMac Administrator Password
Insert the Mac OS X installation disc into the optical drive and restart the iMac, holding down the "C" key while it starts. Release the "C" key when you hear the startup tone.
Alternatively, insert the Mac OS X installation disc into the drive and go to the Apple menu. Select "System Preferences," then "Startup Disc" to select the disc you just inserted to start up your iMac.
When the "Installer" screen appears, select the appropriate language, then click the button to continue.
Select "Reset Password" from the Installer Menu for Mac OS X v10.3, or "Reset Password" from the "Utilities" Menu for Mac OS X v10.4 or 10.5.
Choose the Macintosh HD volume by highlighting it. Select the original administrator's user name. Enter your new password, and click "Save." Quit the Mac OS X installer and restart your iMac.
Don't forget to enter the login password you just changed in "Keychain Access."
Keep your original Mac OS X install discs in a secure place--using the discs, anyone can access and change your iMac's password.
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