Bug#592564: document unusual but supported file system configurations

[Carsten Hey <carsten@debian.org>]

* Russ Allbery [2010-08-10 16:47 -0700]:
> Debian supports /usr as a separate file system from /, /usr as a remote
> file system, and /, /usr, and /etc mounted read-only ...
>
> Since these requirements keep catching people by surprise, I think we
> should write them down explicitly.

Actually the policy refers to the FHS which already mentions part of
what you wrote, but writing down it explicitly to accentuate this sounds
like a good idea.

[http://www.debian.org/doc/debian-policy/ch-opersys.html]:
| The location of all installed files and directories must comply with
| the Filesystem Hierarchy Standard (FHS), version 2.3, with the
| exceptions noted below ...

[http://www.debian.org/doc/packaging-manuals/fhs/fhs-2.3.html]:
| /usr, /opt, and /var are designed such that they may be located on
| other partitions or filesystems.

/var and /boot could be added to "/usr as separate file system from /".
Read-only mounting /etc seems to imply that it can also be on a separate
file system (although I never saw such a setup), so this one and maybe
others could be added too.


Carsten