The whole FH can be shared by NFS root, except /var, which cannot 
be shared entirely and /run (formerly /var/run) which cannot be shared 
at all - talking about Debian's FH.

     The problem is /var/lib which must be carefully separated in two 
parts to distinguish applications which keep common data (eg apt) and 
applications which keep hardware-related data (eg ntpd). Then a few 
dirty tricks are necessary to make the two categories look like they are 
all in /var/lib.

     I don't know if the question of sharing the FH through NFS is 
seriously addressed by the FHS; but, if it is, it fails.

     Didier