Troubleshooting/repair utility. AppleJack is a tool to make it easy to troubleshoot your Mac when no other startup disk is available to you. The script gives you an interactive menu-driven environment for basic disk check/repair, permissions repair, .plist validation, cache cleanup, and swap file removal. You can do basic system maintenance even if your GUI won't start up at all, simply by booting into single user mode, and typing 'applejack'.