Diskless, Low-Form-Factor OpenBSD Systems

In a
previous article
we built a tiny OpenBSD system out of a Soekris miniature PC, a
bootstrap workstation, and a Compact Flash (CF) card. While this
combination works nicely for many purposes, once you have Soekrii
scattered all around your network, managing the CF cards
can be annoying. Replacing the CF cards with a diskless boot system
eases
management problems. One modest server can manage many small diskless
devices,
and it's possible to do much of the system administration on the server
instead of on
the devices. This time, we'll build an OpenBSD diskless device;
netbooting FreeBSD and NetBSD will have their own future articles.
Your server must be a NFS server capable of running dhcpd(8),
rarpd(8), and tftpd(8). The server operating
system
is irrelevant; any BSD, Linux, or even a commercial UNIX will work. I
chose to
use a FreeBSD server, simply because I had spare capacity on a
server-grade
system. (My OpenBSD bootstrap station is a Celeron 433 with a 10GB hard
drive. The original desktop user complained that it was unusable, but
the problems disappeared when we removed the original operating system.
It's perfectly adequate for any free UNIX, but not exactly what you
want in a server.)
Experimenting with an NFS server, rarpd, and tftpd
probably won't affect your environment, but doing unfamiliar things to
the DHCP
server most certainly can, so the main corporate LAN might not be a
wise choice
for your test bed. For my initial experiments in diskless booting, I
installed a
second network card in my diskless server and ran a crossover cable
between
that NIC and the Soekris box. Running a private DHCP server on that
interface
allowed me to experiment freely without corrupting the corporate
network.
While developers asking, "Why did my machine boot something other than
Windows?" would be amusing, it would cause too many meetings.
Soekris Preparation
To configure your Soekris box to run properly diskless, you need the MAC
address of its Ethernet port.  Find this by booting the Soekris with a CF
card and running ifconfig(8), or by using a packet sniffer such as
tcpdump or Ethereal.  When the Soekris boots, it will attempt to grab its IP
address via DHCP; you can always watch the DHCP logs.
All of the rest of our work takes place on the server.  (That's kind of the point, you know.)
Bootstrapping
In the first stage of a diskless boot (as described in diskless(8)),
a PROM or stage-1 bootstrap fetches a boot program from the diskless boot
server.  Where can you find such a bootstrap for OpenBSD/i386?  Google reveals
a variety of sources, but I chose to go with GRUB for OpenBSD.
Cedric Berger has patched GRUB modified to disklessly boot OpenBSD
.

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