[syslinux] Debugging memdisk loaded via pxelinux

Gene Cumm gene.cumm at gmail.com
Sat Oct 22 10:11:39 PDT 2011

On Sat, Oct 22, 2011 at 12:59, Michael T. Davis
<DAVISM at ecr6.ohio-state.edu> wrote:
> At 08:36:27.26 on 22-OCT-2011 in message
> <CAD0RxenXopH-Bu_qjascNqYfMCFd=eEKQ_Y5z7U4k9830Pym4w at mail.gmail.com>, Gene
> Cumm <gene.cumm at gmail.com> wrote:
>>On Fri, Oct 21, 2011 at 23:10, Michael T. Davis
>><DAVISM at ecr6.ohio-state.edu> wrote:
>>>      I have a USB flash drive that I'd like to image, and then load that
>>>image via pxelinux and memdisk.  The flash drive was formatted under
>>>Windows 98 SE as FAT, and boots just fine on its own.  The PXE boot process
>>>gets as far as loading the image via memdisk, but then when the boot process
>>>switches over to the RAM disk, it fails:
>>> [...PXE diagnostic information...]
>>> Loading boot sector...booting...
>>> Invalid system disk
>>> Replace the disk, and then press any key
>>>Aside from re-keying all the information I can see on the PXE client/target
>>>identified as "[...PXE diagnostic information...]", is there some way to log
>>>this data so that I can cite it here?
>>>      My DHCP/tftpd server is tftpd32 from tftpd32.jounin.net, running under
>>>Windows XP Pro SP3.  I'm using a distribution of syslinux v4.0.4 (from which
>  I
>>>obtained pxelinux.0 and memdisk) I found via Google (since the syslinux site
>>>is down).
>>Are your partition(s) aligned to cylinders on the UFD?  I'd consider
>>using fdisk to see what geometry is being used on the UFD then feed
>>that information to MEMDISK (see doc/memdisk.txt for the parameter
>        You don't specify, but I suspect you're talking about fdisk from a
> *ix distribution, right?  I have access to CYGWIN and Mac OS X.  Will fdisk
> in either of those environments work?  If so, do I just invoke `fdisk <dev>'
> for the necessary information, then use that for MEMDISK's {c|h|s}=n options?

If fdisk in DOS bothers to show geometry, that's also suitable.  Yes,
MEMDISK normally guesses the geometry and marginal devices cause
failures in the guesses.

>        FWIW, I haven't done any special partitioning on the UFD; I just
> formatted it under Win98 SE and requested installation of system files, so it
> would boot.  As such, I believe there's only one partition.  I understand,
> however, that you're referring to alignment of the partition relative to the
> cylinders, not the number of partitions.

So it was probably partitioned by the manufacturer.  It'd still be
good to check it out.  Yes, alignment of the partition relative to the
cylinders and ensuring it's the normal fashion.  If it's not, that
alone will cause MEMDISK to guess poorly.

>        I'm at home without access to the UFD or my test environment over the
> weekend.  I do remember seeing the following during the image load, though:
>  Memdisk: Image seems to have fractional end cylinder

Not unusual but a good reason to check things out.  You may also
consider shrinking the partition to perfect standard alignment then
taking an image so the image ends on a whole cylinder.

> I hope to gather what information I can over the weekend and apply it when I
> return to work on Monday.  I appreciate this as a starting point.


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