Preparing to Install MFSBSD Loader on Disk

Martin McCormick martin at
Mon Feb 15 18:31:03 UTC 2010

	When one is logged in to a FreeBSD system, an attempt to
write to the mounted file systems on /dev/ad0, for example,
fails with "Operation not permitted." This is a wonderful
feature 99% of the time because this is disastrous to any
future access after that point.

	The only exception to this is if one wants to remotely
rebuild the system at which point one needs to do something like

dd if=mfsboot.img of=/dev/ad0

	This is, of course, the end of all access to that drive
as we presently know it so a reboot is the only other option and
one must hope and pray that the mfsboot install worked.

	My experience so far is that mfsbsd works well but I
would like to be able to do the whole operation without mailing
out labeled CDR's or USB sticks. Each of our remote sites has 2
FreeBSD boxes and I can just see a hurried individual
accidentally switching the media so we not only loose contact
with the system we are rebuilding, but the boot CD will bring up
mfsbsd on the very IP address of the backup system, crashing

	One could use a temporary third address on the network
that isn't either system A or System B, but I think I can use
the parametric values in mfsbsd to configure the new server so
it would be best to use the same addresses as normal for each
device because of multiple firewalls that one may discover too
late are not set right to allow the upgrade.

	I have been messing with automation for about 35 years
and one of the few things I learned was that Murphy is naive and
overly optimistic. 

	In this case, Plan B is to have 1 CDROM on hand at the
remote site in case we loose the box. That CD could have mfsbsd
set to a third address and then also contain the boot images of
both systems.

	My question today is whether there is any way to
remotely get the mfsbsd.img data written to the boot drive and
execute the reboot command.

	A document I read on this topic tells you to scp the
image to the target system and then, as root, use dd to write it
to disk. I was root when I discovered I couldn't do that.

	Thanks for any answers and, Kids, be really careful
here. The dd operation totally destroys all existing partitions.
What you get is partitions 1-3 are unused and partition 4
contains the mfsbsd image that will create the virtual disk with
a baby OS when the reboot happens.

	Since you start with no actual drives mounted, you can
reformat the hard drive to however you need it, but you can't
reboot again until there is a working system back on the hard
drive or you just get a warm, humming paperweight. That's when
you need the rescue CD.

Martin McCormick WB5AGZ  Stillwater, OK 
Systems Engineer
OSU Information Technology Department Telecommunications Services Group

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