looking for error codes

[perryh at pluto.rain.com]

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 :)