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My friend bought an old iMac at a garage sale. It's locked, no start up discs. The people he bought it from have moved already. We don't know where. How can we get into the computer without the usernames and passwords?

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4  
Define: locked. –  Bobby Jun 12 '12 at 7:05
    
Also, what version of OS X is on it? –  slhck Jun 12 '12 at 12:27
    
Great, sell your computer and leave user accounts and possibly personal data on it. Startup discs can be found using bittorrent or a mac geek friend will have them. –  Moab Jun 12 '12 at 14:16

2 Answers 2

If you're running OS 9, you may need another mac (though i suspect a PC with firewire and a HFS driver would do) and a firewire cable. You will need to delete preferences pertaining to keychain access and any keychains in the preferences folder in the system holder (source). The first imacs ran this so its plausible

If you're running OS X on the imac

Single user mode would do the trick unless there's open firmware password protection in place

To go into single user mode

  1. Press the power button to start the computer.
  2. Immediately press and hold the Command (Apple) key and one of the following: the "s" key for single-user mode. (Command-S) This should boot into a white screen, and iirc throw you into a command prompt

These instructions should work for older versions such as 10.4. Khafshoh S' version works for newer systems 10.5 and better - 10.7 also has yet another option for resetting the password involving the 'resetpassword' command in lion recovery.

Instructions for changing the password are based off here

You would then mount the file system as writable with

mount -uw /

then find out what the accounts on the system are with

ls /Users/

then change their passwords with

passwd username

reboot and get back into graphical mode with

reboot

Then check the accounts to work out which one is the admin account.

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You guys are awesome. I was doing pretty well following your instructions but got hung up on root # and while playing around with that came upon master password hint: Mrs. Homer. Doh! Typed in Marge, and I'm in. –  Meg Jun 15 '12 at 23:02
    
Oh, you could/should probably post that as an answer and select that then. Otherwise, the question will get bumped up every so often as unanswered. –  Journeyman Geek Jun 15 '12 at 23:54

You should choose one of these options mentioned here:

How to Hack the User Password in Mac OS X Without an OS X CD. | OSX

  • Boot into single user mode (press Command-S at power on)
  • Type fsck -fy
  • Type mount -uw /
  • Type launchctl load /System/Library/LaunchDaemons/com.apple.DirectoryServices.plist
  • Type dscl . -passwd /Users/username password, replace “username” with the targeted user and - “password” with the password you wants.
  • Reboot

or

  • Reboot
  • Hold apple + s down after you hear the chime.
  • 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
  • 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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Interesting that there's two methods to do this. The one i've suggested is similar to the standard unix way of doing things. I'm curious to what dscl is, since its not something i've come across so far. Any ideas? –  Journeyman Geek Jun 12 '12 at 12:25
1  
Don't run around begging for votes. If that's really the only reason you're here, you're in the wrong place. I would start by not copy and pasting your answers from other sites, because this is plagiarism and not encouraged. –  slhck Jun 12 '12 at 12:56

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