AppleJack runs as a Terminal application, making it easy to perform maintenance tasks in Single User mode (click for larger view).Īfter installing AppleJack, you will be able to run it by booting directly into Single User mode (hold Command-S) at start-up, which will drop you to a command line with root privileges. AppleJack so far has been incompatible with Snow Leopard, but with today's update the Snow Leopard incompatibility has been squashed. With Leopard and prior versions of OS X, one of the popular maintenance utilities was AppleJack, which is a free SourceForge project and ran in the Terminal (preferably Single User mode) as an easy-to-access way to run a bout of cleaning functions on the Mac.