Note: large portions of this review have been taken from the .rtf file that comes with the Applejack Download. I couldn't have expressed it any better than the developer and re-inventing the wheel is not my purpose.
Are you having strange errors, failure to load or other problems with your Macintosh? Are some "Clean-up" utility programs too complex/scary for you? Good news, a solution is available that cures many problems, performs system maintenance and is simple and safe to use. While the program is free to download and use. I do recommend a donation to the developer. He has done and excellent job and deserves some compensation.
I have been using Applejack on my three Macs using systems 10.4.n, 10.5.n and 10.6.n for several months with very good results. I've had no problems with it and it has kept my systems running smoothly and in top condition. It takes only a few minutes to run and can perform all tasks automatically while I do something else. Despite the warning about known issues on 10.4, I have never had a problem on my PowerBook running this OSX version.
AppleJack is a shell script intended to assist you in trouble-shooting startup problems in Mac OS X. In many situations it can help resurrect an apparently dead system by cleaning up the mess left by system crashes: disk directory errors, buggy caches, corrupted preferences, etc.
AppleJack is designed to be run only in single user mode. (see below for how to do this) Running this script while logged in as a user can crash your operating system (especially if you use it to delete the system's virtual memory or cache files), which would be a bit counterproductive, because we're out to solve problems, not cause them. The download page is: http://applejack.sourceforge.net/
Beyond these basic functions, AppleJack can also test your RAM (if you choose to install the included memtest), disable auto login, disable login items for a user, bless a new System folder, and more. These last options are only available from the expert menu (accessible by hitting x from in AppleJack's main menu), and should be considered experimental at this point. That means don't use it unless you are truly a Mac Master and have your system install disk handy.
APPLEJACK REQUIREMENTS 1. AppleJack v 1.6.x requires Mac OS X 10.4.x, 10.5.x or 10.6.x on Intel or PowerPC (but see known issues for 10.4, 10.4.1, 10.4.2). For Panther and Jaguar users, please use the latest 1.4.x version available.
2. The ability to boot into single user mode (some users may be locked out from single user mode because of corporate IT policies and open firmware security locks).
3. A wired keyboard, unless you are using Mac OS X 10.4.3 or later. (Previous versions of Mac OS X do not support wireless keyboards in single user mode.) 4. An ability to read documentation, and follow instructions. ☺
INSTALLATION Mount the AppleJack disk image, (the downloaded .dmg file) by double clicking it and run the AppleJack.pkg installer.
If you'd like to install the included Memtest OS X RAM testing utility, choose customize during the install, and select the Memtest OS X check box. Installing Memtest with AppleJack allows you to run RAM tests from within AppleJack (only in "Expert Mode"described in the Applejack .rtf file).
1. You can type 'man applejack' in a terminal window for complete usage instructions.
2. Restart your computer. When the "bong" sounds, hold down the Command and s keys until you get lots of white text appearing on a black screen. You are now in single user mode. If you've used the installer, you should just be able to type 'applejack' at the prompt, press Return, and be on your way.
3. Auto mode: You can let the script run through its tasks automatically by typing 'applejack auto'. If you want the machine to automatically restart at the end of its tasks, use 'applejack auto restart'. You can also tell the computer to shut down automatically at the end by using the command line 'applejack auto shutdown'. You can also simply enter "a" at the prompt and press return. Note that you will see strange things on the scene while Applejack is running. It may scroll very fast during some tasks like Repairing Permissions. This is normal. Don't worry, be happy. When Applejack finishes all tasks, you will be able to select "restart" or "shut down" by pressing 'r' or 's' then Return.
3a. Deep Auto mode: If you want to let AppleJack clean out all cache files, including the Launch Services database and any cached User Pictures, use 'applejack AUTO' instead. Use this if you still have problems booting after running AppleJack already.
4. Interactive mode: To run through just one task, or to run the script manually, type 'applejack' and then choose tasks from the menu. Running the script in interactive mode has the benefit of giving you options for working with user level cache and preference files, not just the default system level caches and preferences. To select an option, type the highlighted number or letter associated with the action, and then hit return. Whenever you enter a choice in AppleJack, you will need to press Return for that choice to take effect.
We can see from these sample instructions that Applejack is powerful, yet easy to use. If you've never done single user mode before, the first time can be a little intimidating as few people these days are accustomed to command line interfaces. For me, it is a nostalgic trip back to the days of the DOS days (Pre-Macintosh) when it was always C:\ chg dir\ a: files or some obscure hieroglyphics like that. After the first time, you go through it, everything seems easy, if a bit strange.
I recommend using Applejack about once a month as a preventive maintenance measure. I like the no-muss, no-fuss method of auto mode. Then I do a normal restart and all is well. ☺