Boot in Single User Mode in Mac OS X

5th May 2009
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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.

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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 WordPress, Shopify, Rails, Python, and ASP.net/Umbraco frameworks.