> In Solaris 8 the mnttab is no longer writeable like in 7 and below.  NBU
> wants to change the access time for purposes of incremental backups, but
> can't.  And you can't make mnttab writeable even if you wanted to, it's
> not a real file anymore.

There is a special filsystem type `mntfs'. What is happening is that a
kernel data structure is being mounted as a filesystem/file. This idea
of mounting kernel data structures as file systems, was first done, to
my knowledge, in Ninth Edition Unix, ~1988.