Hello Erik,
EA> - A root device: if you don't have a hardrive you can use a
> memory disk embeded in the kernel (like in the installation-
> kernel) or NFS.
I'm keen to try the memory disk idea. I plan to build a firewall soon
and would like it to have just a CD-ROM drive. Some (which?) parts of
the filesystem need to be read/write. If they're small enough, I can
have the rest mount read-only.
EA> - Your own statically linked /sbin/init on the root device. This
> is the only userland process started by the kernel so if your
> system only need to run one program call it init and place it
> in /sbin. (Your program might have to do some of the things
> that the original init does, e.g. if your program wants do
> console io you will need a /dev/console and your init will
> have to open that device and dup2 fd's 0, 1 and 2 to that fd).
I think I get understand what you're saying, and where the application
is simple and space is at a premium I can see the sense in that
approach. I'm not sure I'll try it just yet though ;-)
EA> You can of course use the standard init and instead creat your
> own /etc/rc.
That sounds like the direction I'll take.
EA> If you want dynamically linked programs you will also need a
> /usr/lib filled with the libraries your programs use (running
> ldd on a binary will list does) and /usr/libexec/ld.elf_so is
> also needed.
Hmm... can /usr/lib be read-only?
EA> Some programs (like netstat) need to lookup data in the kernel
> and for that they need the kernel symbol table. Normally the
> symbol-table is read from /netbsd but if you use a memory disk
> embeded in the kernel you might not want to put a kernel there
<grin>
EA> ...If that is the case you can use kvm_mkdb (8) to create a
> /var/db/kvm.db that will be used instead.
I'll look that one up, I can see myself using it when I get to ROM or
Flash based systems. For the machines with CD-ROM drives, could
/netbsd be a link to the kernel on the disc?
EA> If you use existing programs you will of course need to lookup
> what libraries they need (if dynamically linked), what config
> files they use, other directories (e.g. they might want to put a
> log file in /var/log) and if they exec other programs.
It sounds as though I have plenty of homework to do! :-)
EA> That's all I can think of for the moment.
Thanks a lot, you've given me enough to get started and that is
appreciated.
Regards,
- Andy Ball.