Many Linux newbies are confused by this when they see it, usually from a fsck. They're prompted and given a root shell, when they don't really know what the problem is.
It's simple to resolve. Usually just # fsck /dev/some_partition. For example, # fsck /dev/hda5. Yes, it's also a good idea to remember what partition is what. fsck it, it will prompt you for things, and usually it's safe to blindly say yes to everything. Lost data will be sent to the partition's "lost+found" directory. Lost files are sorted by inode rather than what its filename was, so it's a good idea to use the file command to figure out what kind of data it is. If file just comes up with "filename: Data" or the like, try opening it with a few common programs such as vi, ee, StarOffice, whatever. | 
