[Beowulf] cloning issue, hidden module dependency

David Mathog mathog at caltech.edu
Mon Dec 8 16:55:09 EST 2008

Joe Landman wrote:
> Well RHEL is annoying in that if you decide to use a custom kernel and a 
> software raid, you are, for lack of a better term, toast (if you stick 
> with their tools/config).

My compute nodes aren't that complicated.  

The straw that broke this particular camel's back was a decision
(presumably by Mandriva, maybe by RedHat) to change in the kernel
config BLK_DEV_IDE and BLK_DEV_IDEDISK from y to m, similarly,
DEV_AMD74XX (and etc.) also changed from y to m.  As a consequence, they
went from a system where a simple initrd would boot anywhere (as all the
needed drivers were built into the kernel) to one where a much more
complex initrd ended up being highly machine specific.  In terms of
having it "just work", having the disk drivers built into the kernel is
lot simpler.  Ubuntu 8.04.1 also has these as modules, and it has an
immense initrd.  (Even so, it might not have worked on my S2466
systems because the initrd did not build an AMD74XX module.)

On the plus side, I did finally figure out how to PXE boot the PLD
rescue CD, which in the last week has helped me escape from a couple of
tight spots.  The tricky part was that the online instructions said
to use this in the APPEND line:


and that doesn't work, at least not for me. The two cpio archives are
treated as if it was one file name, which of course does not exist.  For
future reference, it is done this way:

1.  download and mount the PLD rescue cd ISO, copy the file hierarchy
into /tftpboot/rescue_pld_201 (or whatever)

2.  Put this in /tftpboot/pxelinux.cfg/default
  KERNEL rescue_pld_201/boot/isolinux/vmlinuz
  APPEND initrd=rescue_pld_201/rescue.cpi root=/dev/ram0

3.  Put this in /tftpboot/message.txt
PLD_X86_201 : PLD rescue disk 2.01 (hdX disks)

PXE boot a node, chose PLD_X86_201 on the PXE menu on its console, and
it comes up at the text prompt for the PLD rescue CD.  This provides a
lot more tools than boel, but it is still light enough at 58M to boot
over a 100baseT network.


David Mathog
mathog at caltech.edu
Manager, Sequence Analysis Facility, Biology Division, Caltech
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