Applejack is a command-line application for rescuing your computer when disaster strikes, or threatens to strike.
Don’t let the “command-line” bit frighten you off. Applejack is probably the easiest-to-use command-line application I’ve ever seen. It was built for ordinary people to use, and won’t bamboozle you with geekspeak.
First, you need to have it installed. Download Applejack and double-click the installer – it will do what’s required. Then you can forget about it, until the day comes when something’s gone weird on your computer.
The precise nature of “weird” is hard to define. You might find applications behaving oddly, or crashing, or just not working at all. If weird stuff is happening, Applejack might be able to help.
To use it, the hardest thing you have to do is reboot into Single User Mode. To do that, restart your Mac and hold down the Command and S keys. Instead of the usual OS X desktop, you’ll end up at a scary-looking terminal prompt, plain white text on a black background.
Now all you need to do is type “applejack” and hit return.
You’ll see a simple list of commands, each with a number. Like in the screenshot above.
Hit “a” to run Applejack in autopilot mode. It will go through a series of scripts, all of them designed to clean up any mess on your hard disk, tidy up caches, fix dodgy files, and generally leave the system in good condition.
Be warned: Applejack is very useful when you’re in Single User Mode, but don’t try running it at any other time – you could do serious damage.
Applejack is free, and one day it might just save your skin. Or at least your important files. Highly recommended.