How can I unlock single-user mode?

I stupidly forgot the password to my MacbookPro. I have locked single user mode 2 weeks ago (for security reasons). How can I unlock single-user mode to get my password back?

3 Answers

Here's something you can try from hackmac.org's article "Access Single-User Mode When Locked":

Procedure

1) Change the Amount of RAM

Change the amount of RAM inside the computer. It doesn’t matter if you add RAM or remove RAM, but the amount of RAM has to be different than the amount present when the computer was last turned off.

Be careful when handling RAM. It is very sensitive to static electricity.

2) Reset the PRAM and NVRAM

Once you have successfully changed the amount of RAM, and preferably closed the case back up, turn the computer on. Once you hear the chime signaling that the computer is turning on hold CMD+Option+P+R. Hold them down until the computer restarts and you hear the chime for a second time. Immediately after you hear this second chime release the keys, then quickly press them again. Wait until it restarts and you hear a third chime. Then repeat for a fourth time. (Note: This is resetting your computer’s PRAM and NVRAM)

3) Boot into Single-User Mode

Once you have heard the fourth chime hold CMD+S. This will boot you into single-user mode. From here you can perform whatever actions you want to do, but be careful not to change anything vital to the running of the computer.

4) Replace/Remove RAM

Turn the computer off and put the original amount of RAM back inside. This step isn’t necessary but is highly recommended.You should try to leave the computer as close to its original state as possible.

Again remember that opening up a Mac does void its warranty.

This should work on both EFI (Intel) and OFI (PPC) based Macs. This is a hardware based hack, proceed with caution! We are not responsible for anything that may go wrong in the process. Essentially you are removing the system RAM and reinstalling it. Here are the steps for a MacBook:

1. Shut down your computer
2. Remove the battery
3. Remove the three Phillips head screws that are on the L-bracket
4. Remove the L-bracket
5. Slide one of the levers (it doesn't matter which one) to the left; this will release the RAM
6. Gently wiggle the RAM card out and put it aside, you will put it back later (do not touch the gold bars on the front, you could break it)
7. Replace the L-bracket and put the battery back in
8. Boot up the computer while holding Command+Option+P+R (this resets the parameter RAM)
9. Wait for the startup chime to sound 3 times
10. Release the keys and shutdown the machine once you reach the login screen
11. Remove the battery and L-bracket, replace the RAM module and slide the lever back while pushing it in until it does not wiggle anymore
12. Replace the battery and L-bracket
13. Now if you boot up the machine you should bypass the Mac firmware password.

You can now use the machine as usual, boot from an external drive, or whatever else.

There are several reasons why your Mac may not boot into Single User Mode. If any of the following are true, you will need to reset the specific settings and / or modify your hardware usage accordingly before you can boot into SUM.

1. You have FileVault enabled - disable file vault
2. You have a firmware password set - remove the firmware password
3. You are using a wireless / bluetooth keyboard to attempt to boot into SUM - the bluetooth driver only activates after the startup chime sounds. Use keyboard on laptop or plug in a wired keyboard.
4. You have Hard Drive / Partition Errors - correct the disk errors and boot into SUM.

Summarized from CNET