Date: Fri, 14 Nov 2008 20:45:34 +0100 From: Luigi Rizzo <rizzo@iet.unipi.it> To: stable@freebsd.org Subject: diskless+pxe notes Message-ID: <20081114194534.GA64986@onelab2.iet.unipi.it>
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Hi,
i finally decided to try and use pxeboot to replace the etherboot
method I was using so far for diskless setups.
The goal is to fully share the server's root and /usr directories,
as documented in diskless(8). I'd like to share the following
notes, hopefully to go in the manpage.
cheers
luigi
-------------- root path configuration -----------------
There seems to be a well known problem in pxeloader, see
kern/106493 , where pxeloader defaults to using a root path of
/pxeroot when offered "/" . The patch suggested in
http://www.freebsd.org/cgi/query-pr.cgi?pr=106493
is trivial and judging from it I believe this is addressing a
true bug and not a feature. Fortunately there is a workaround
(suggested in the PR) which is using "//" as a root path.
------------- sharing /boot with the server ---------------
I believe it is quite useful to share the whole root
partition between the server and the diskless client.
This would require at a minimum some conditional code
in loader.conf (or loader.rc, etc) so that at least you
point to different kernels.
A minimalistic approach can be adding this line to /boot/loader.conf
bootfile="kernel\\${loaddev};kernel"
The variable $loaddev contains the name of the load device,
which is "pxe0" in the case of pxeboot, and disk* in other
cases when loading from the local disk.
If you make sure that there is no 'kernel.disk*' on the
directory, and instead there is a kernel.pxe0 in the same
directory, then the diskless machines and the server will boot
from the proper file.
Unfortunately i don't know how to implement a conditional
in /boot/loader.conf -- otherwise one could do much nicer things
such as differentiate which modules to load and so on.
--------------- pxeloader bug in 7.x ---------------------------
Also worth mentioning is an annoying bug in pxeloader as compiled
on 7.x, see http://www.freebsd.org/cgi/query-pr.cgi?pr=118222
i.e. the pxeloader in 7.x fails to proceed and prints a message
"can't figure out which disk we are booting from".
The workaround is using a pxeloader from FreeBSD6 works.
I guess this is a compiler-related problem (given that 6.x uses gcc 3.4
as a compiler, while 7.x uses gcc 4.2).
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