While I am at it, let me add the OTHER condition that can come up. In addition to the lower-level disk structure, which fsck and Verify Disk deal with, and the high-level permissions that "Repair Permissions" deals with, there's potentially problems that happen with the directory structure. fsck and "Verify Disk" are supposed to deal with this, but sometimes their repair-fu is not powerful enough.
For this case, I strongly recommend Disk Warrior, from Alsoft. You can make a bootable CD which you can then run, and it will do a huge amount of detective work and testing to determine what the directory structure SHOULD be, and then allow you to replace it in a failsafe manner. (Even it occasionally hangs or fails, though.)
This can save your butt. Rarely, but it's cheaper than recreating data for angry clients.
no subject
For this case, I strongly recommend Disk Warrior, from Alsoft. You can make a bootable CD which you can then run, and it will do a huge amount of detective work and testing to determine what the directory structure SHOULD be, and then allow you to replace it in a failsafe manner. (Even it occasionally hangs or fails, though.)
This can save your butt. Rarely, but it's cheaper than recreating data for angry clients.