Why does / change size with mail?

[Johannes Viegener UB Karlsruhe]

> However, my mailbox is in /usr/spool/mail which is in "/usr", a separately
> mounted partition (and thus shouldn't affect "/").  I thought that maybe it
> was because when I was using mailtool (SunOS4.1.1; SS1+; OpenWindows) a file
> containing the full mailbox was being kept in "/tmp" which uses up "/"
> space, but there is no use of "/tmp" at the time.
>
> Could someone please explain this phenomenon to me?
>

On my ULTRIX-based workstation the directory /usr/spool is linked to
/var/spool. On most UNIX-machines the /var directory is part of the
root ( / ) filesystem (Not on my ULTRIX-stations, where the /var-
filesystem is a separately mounted partition). I think SunOS will
use a similar layout of spool-directories, because the /var-filesys.
contains machine-specific-files, which can not be shared on a network
between multiple machines. But the /usr-filesystem contains primarily
files which can be shared for saving diskspace.

Ciao Johannes