AppleJack is a great troubleshooting assistant for Mac OS X. With AppleJack installed, you can troubleshoot a computer even if Mac OS X won’t fully start, or don’t have a startup CD handy.
We recomend AppleJack in our tiny-but-popular My Mac Won’t Start! guide. We’ve been holding back this tip for a new version that is compatible with Apple’s new Intel-based Macs. Happily, version 1.4.3 which adds Intel-compatibilities was released this month.
The main AppleJack Project Page can be found on the SourceForge.net website. However (ironically) the SourceForge website does not work well with Apple’s Safari web browser, so we recommend visiting this MacUpdate link to download the latest version of AppleJack:
AppleJack runs in Single User Mode and is menu-based for ease of use.
Step 1. Hold down Command-S while you turn on your Mac. You should see a black screen with white text. Don’t panic.
Step 2. At the prompt type: “applejack” and hit return.
Step 3. Follow the menu-based instructions to run several types of disk and system repairs.
Tip: If you want AppleJack to run repairs automatically and then restart your Mac, type “applejack auto restart” instead. This is what we usually do.
Using AppleJack, you can repair your disk, repair permissions, validate the system’s preference files, and get rid of possibly corrupted cache files. In most cases, these operations can help get your machine back on track.
Source: We’ve been using AppleJack for years. At Creativetechs we recommend installing AppleJack on all our clients’ workstations. Once installed you may not need to see it again unless you run into problems.