> Actually, given what badsect does, you HAVE to run it on a mounted
> file system: it uses mknod() to create a bogus inode which owns the
> bad sector.  You then IMMEDIATELY reboot and let fsck discover that
> there is a PARTICULAR kind of peculiar bogus file in a PARTICULAR
> directory (/BAD), and it winks at you and asks if you want the bad
> block noted (by converting the bogus inode into a real file that
> honestly owns the block).

In my experience you must fsck twice before the filesystem will be
clean, so reboot to single user mode and run fsck manually.