4.2BSD installation mystery ...

[thomas at utah-gr.UUCP]

The kernel (pre 4.2, anyway) keeps a copy of the superblock for every
mounted filesystem in-core, and only writes it out to the disk i.e., the
disk copy is never reconsulted.  So, if you fsck the raw copy of a
mounted filesystem, and it modifies the superblock, then you are in big
trouble, because what's on the disk doesn't agree with what the kernel
thinks is there.  In 4.1 (and maybe others), you CAN fsck the block
device, as long as the filesystem is "quiescent" (sp?).  I think in
earlier versions, the situation was even worse, but I don't remember the
details now.

=Spencer