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Re: i386-pc pxe boot foiled by Dell Precision T5610

From: Jordan Uggla
Subject: Re: i386-pc pxe boot foiled by Dell Precision T5610
Date: Mon, 5 May 2014 10:42:02 -0700

On Sat, May 3, 2014 at 11:49 AM, Chapman Flack <address@hidden> wrote:
> Hi,
> I've had a PXE net-install setup that has worked very well for a while.
> You can plug any box into our network and boot from network, and you get
> a grub menu with a bunch of generally useful options (memtest86+ for
> anybody, no password, sysresccd with a password, etc.), plus if our DHCP
> server knows what OS and configuration are supposed to be on that box,
> there will also be a submenu with rescue, prompted install, and saved-answer
> install options custom to that box. All this is just background to give
> an indication of how simple/complicated our grub.cfg is. Really it's
> not bad. It's written by hand (not the usual assembled-from-pieces-in-/etc),
> and about 90 lines long. It defines a few functions, and it uses
> net_get_dhcp_option to query a site-local option the DHCP server sends
> to say what should be on the box. If that string is, say,
> "RHEL x86_64 6 5 workstation" then the main grub.cfg will source
> $prefix/RHEL and expect it to define a function RHEL that can be
> called with the remaining arguments, and that function creates the
> submenu with the right menuentries for booting the OS installer with
> the right cmdline arguments. The RHEL script, for example, is another
> 45 lines. Nothing very big at all.
> This whole setup works great on every other box I've used it on, but we
> just bought some brand new Dell Precision T5610 workstations, and the
> behavior is really crazy. Usually it loads grub and parses the scripts
> ok, and puts up the correct menu, but try to load any of the choices and
> it just either hangs or reboots on the first kernel load command (linux,
> knetbsd, whatever). Sometimes it won't accept the pbkdf2 password at all,
> or will say command not found even for something built-in like reboot.
> On occasions when it does accept the password and I can get to the command
> line, it will hang on even something simple like
> testload ($root)/memtest86+.elf
> It is acting very much like something in the grub-script code is stomping
> on memory somewhere. As a test, I moved most of grub.cfg into grub.normal,
> and made a very short grub.cfg:
> set superusers="..."
> password_pbkdf2 root grub.pbkdf2.sha512....
> echo -n 'm for minimal: '
> read min
> echo
> if [ 'm' != "$min" ]
> then
>   source "$prefix/grub.normal"
> fi
> With that, I can boot and enter m and it skips all the rest of the script.
> At the command line I can directly enter the same lines that were otherwise
> hanging....
> testload ($root)/memtest86+.elf fine
> knetbsd ($root)/memtest86+.elf
> boot me a memtest just fine
> and so on. So as long as it hasn't run my other 130 lines of script yet,
> apparently nothing has been stomped on yet. And there's really nothing
> at all fancy in the script - some function definitions, variable assigments
> and uses, uses of setparams and shift, and the one use of net_dhcp_get_option.
> And why am I seeing this problem on these 5610s and not on other boxes?
> Do different BIOSes leave grub with really different amounts of working
> memory or something? Are there any grub commands I can use to see the
> memory stats or anything else that might help pin down where the problem
> is?
> The 5610s have 32 GB of RAM each, and are set for PXE boot in legacy BIOS
> mode. I have played with some BIOS settings that seemed like they might
> affect the memory available to grub, but with no improvement. I even pulled
> some DIMMs just to see if it might work better with less total RAM (32 GB
> is more than most of our other boxes where I don't see this problem). Also
> no improvement.
> Any hints on how to further troubleshoot this? And is there a way to build
> grub to give errors if something in the script code is clobbering memory
> or whatever, instead of just seeming to work until the machine hangs or
> reboots later?
> Thanks,
> Chapman Flack

Please file a bug report about this with: The exact version of grub
you're using (including the distribution package's version if you're
using a binary distribution, or your build log if you're building from
source). The full scripts that you're using, including a minimal
grub.cfg that will reproduce the problem (at least on the problematic

If you can, please also include a serial log with "debug=all", though
the developers will likely be able to give you a more targeted debug
value that will produce less output.

Jordan Uggla (Jordan_U on

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