Boot in Single User Mode in Mac OS X

5th May 2009
All posts

Single User Mode looks daunting at first if you’ve never used it, but it is a powerful tool in your mac maintenance arsenal. Boot your computer to it by holding command + s on restart till you see the black screen with white text (see photo above). This is the command line – be careful: Type the wrong thing and you can do some serious harm to your computer. Follow these steps and you’ll be okay.

[Edit: 4 December 09 – Instructions from macsage.com on how to read a usb drive while in Single User Mode]

[Edit: 14 November 09 – You can use Single User Mode to Change Mac admin password without the disk, but be warned, this is for ADVANCED users only. Users experienced with using the command-line.]

What is Single User Mode?

Before continuing, please read this apple knowledgebase article. Per Apple:

“You can use key combinations to start up the computer in either single-user mode or verbose mode. These may be used for troubleshooting or software development.”

I use Single User Mode (command + s) for more serious issues that aren’t solved by Disk Utility’s “repair permissions” feature, or the same command when booted to the OS X boot disk. I won’t be discussing Verbose Mode here. Even though you’re just running a system check, very much similar to “repair permissions”, it seems doing this before boot really helps clear things up.

How do I use Single User Mode?

The following are the commands to use to make the system check itself and to reboot. When you first see the black screen with white text, don’t panic. Just wait for the white cursor box to appear, after a bit of text shows up first, and type this exactly:

fsck -fy

This forces the system check, is non-destructive and totally safe.

Then, after the process finishes (you’ll know it’s complete when all checks are complete, between 7-8 of them approximately) type this exactly:

reboot

A Word of Warning

While Single User Mode is mainly for developers and you can do some damage I must urge some caution that you don’t type anything else than what I’ve advised here. There are descructive unix commands out there that will wipe your hard drive or worse; you basically have carte blanche when in this mode to do whatever you want. Too much power for most of us!

Hope this helps you keep your mac running smoothly.

Tags:

Nathaniel Flick

I'm a Front End Web Developer passionate about usability. My primary specialties are HTML5, CSS3, SCSS, LESS, and jQuery and I am very familiar with Foundation and Bootstrap frameworks. I've worked on top of and with Rails, Python, and ASP.net/Umbraco back end frameworks.

  • Prudhvi Valluru

    I'm using mac1,1. I previously used bot mac osx, tiger and winxp. Yesterday, I thought of removing winxp. when i'm trying suddenly my laptop stopped detecting internal hard drive. When I'm keeping mac os its processing but not showing hard disk. Isearched even disk utilities there also only os dvd is recognising but not internal hard disk. If I start the laptop without OS disk its showng only white screen nothing else. please help me
    email id:prudhvinag.v@gmail.com

  • Nathaniel

    Sorry, not quite understanding your problem. Maybe answering these questions for me will help me understand what your situation is:

    1. What os x are you running? There is no mac1,1 to my knowledge.

    2. Are you running VMWare Fusion, Bootcamp, Parallels or some other virtual machine to run XP?

    3. What did you remove when you tried to "remove XP"?

  • Prudhvi Valluru

    hi Nathaniel, thanks for reply.mac1,1 is laptop model. Mac OS 10.1x tiger.

    Actually the problem started when i holded C button while system booting.

    Now when i starts the system laptop shows white screen and after some time it blinks a folder symbol with ? symbol on it. Thats it nothing happens.

    2. If I keep mac OS dvd it continues process but not detecting hard drive.

    please help me

  • Nathaniel

    1. Restart, hold the mouse button down and wait for the DVD to eject.

    2. If comp still can't find the OS X you will need to restart and hold the option key till you see a hard drive on screen and some arrows. Here you can choose an op system. Hopefully a drive with an X on it like OS X.

    3. Once the dvd is out of the drive try booting in Single User Mode again to repair permissions.

    4. If it still won't restart you may need to boot in Target Mode (search my blog for the article on this) and back up all your files elsewhere as your computer is in danger of failing either in hardware or software. Neither is good news for your data.

    Let me know what happens.

  • Prudhvi Valluru

    I tried as you told, when i finished 2nd step it showing only arrow but not hard disk. I tried to boot in single user mode but its not taking anywhere. Its just showing white screen with a blinking folder symbol.

    What might be the problem? Is there any chance I can rectify the problem?
    do I have to buy a new hard disk?

  • Nathaniel

    Prudhvi, sounds like your OS X is no longer being recognised, but at least your comp is booting to a screen so that's a good sign.

    I'd use your OS X system disk to try to repair permissions from there (don't reinstall yet).

    If all else fails, back up your data, and then reinstall OS X on your machine.

  • Prudhvi Valluru

    I'd use your OS X system disk to try to repair permissions from there (don't reinstall yet).

    1. I didn't understand your above statement. Please tell me more clearly so that I will try and tell you the result.

    2. How to reinstall, because its not recognising hard disk. When I kept OSX dvd its taking to installation process but to install its not showing any hard disk.

  • Nathaniel

    Sounds like your hard disk is unreadable. I'd stop what you're doing and take it to a licensed Apple tech. Make sure they can get your data off that drive before they do anything.