what is FSCK and why do i have to do it?

man fsck

fsck = File System Check.

Everytime you start your Mac, there's a little spinning wheel. That's the fsck being done automatically for you.

Sometimes if you're having troubles with your Mac and you don't have access to other integrity utilities, you can try doing a manual fsck when booted in Single User Mode.

 

You've probably noticed some posts on, "my computer won't boot" or "I get a flashing ? mark"

Both of these can be due to file system/catalog errors on the HD -- basically the HD gets corrupted enough it won't boot, though people usually see the spinning ball quite frequently before this happens.

All fsck does is check the file system/catalog for errors and repair them, you can also run Disk Utility/Disk First Aid (but that requires a CD/DVD.)

fsck doesn't require a CD/DVD and is something that can be done in a couple minutes when you turn the machine on -- just boot into single user mode and follow the directions on the screen.

 

Wow, I didn't know that. Is that all it's doing, or is it also performing other system functions?

 

Check out /etc/rc.boot.

 

If you are running 10.3 or later, the file system is journaled, by default, making the manual use of 'fsck' virtually obsolete. If your filesystem does become corrupt (kernel panic, power failure, etc.), the filesystem journal is used to reconstruct it. If it can't, you probably have a bad disk or a serious low-level bug, neither of which are likely to be repairable by 'fsck'. It certainly doesn't hurt to try running 'fsck' in these circumstance, it's just that you may well be SOL, at that point.

 

One of the things that occurs while that spinning wheel is on screen is a RAM test. The more RAM in your Mac, the longer this test takes.