looking for error codes

[Paul Schenkeveld]

On Sat, Apr 02, 2011 at 12:50:29AM -0700, perryh at pluto.rain.com wrote:
> Mehmet Erol Sanliturk <m.e.sanliturk at gmail.com> wrote:
> 
> > For a long time I am thinking to obtain a physically ( not only
> > software ) based [read-only] FreeBSD edition by re-arranging some
> > parts of it , but I do not know how to do it ...
> 
> > After some years , MFM hard disks abandoned in favor of IDE
> > ( Integrated Drive Electronics ) hard disks by moving controller
> > to hard disk and eliminating use of add-on cards with a very
> > unfortunate design decision as ( a write protect mechanism by
> > a switch on the hard disks are not implemented ) .
> 
> At least some IDE drives have write-protect jumpers, which could
> presumably be replaced with connections to switches.
> 
> > With respect to my knowledge , no one of the operating systems
> > has a facility to separate read-only and modifiable parts ...
> 
> SunOS 4 had a partial solution to this, by rearranging the FS layout
> so that /usr could be mounted read-only (and often, from a server --
> IIRC a single /usr could be shared among multiple diskless clients).
> They used quite a few symlinks so that things could be found in
> their accustomed places although actually located elsewhere.  The
> scheme was fairly well described in the SunOS 4 manual set; granted
> _finding_ a SunOS 4 manual set these days may be a challenge :)

In fact, FreeBSD is very similar, /etc and /usr/local/etc may be
written to for configuration purposes after building your system,
/tmp and /var should really be writable (temp files, log files,
sockets etc.) /home other application directories of course depend
on the particular application and the rest can be r/o.

Embedded systems (please read the freebsd-embedded mailing list) deal
with similar issues and that's what nanobsd(8) was written for.
Read http://www.psconsult.nl/talks/AsiaBSDcon2010-Servers if you want
to see that similar techniques can also be applied to servers.

Regards,

Paul Schenkeveld