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<TITLE>The Answer Guy 36:
Persistent Boot Sector
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<H4>"The Linux Gazette...<I>making Linux just a little more fun!</I>"</H4>
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<H1><A NAME="answer">
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<font color="#B03060">The Answer Guy</font>
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<BR>
<H4>By James T. Dennis,
<a href="mailto:answerguy@ssc.com">answerguy@ssc.com</a><BR>
Starshine Technical Services,
<A HREF="http://www.starshine.org/">http://www.starshine.org/</A>
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<!-- begin 79 -->
<H3 align="left"><img src="../../gx/dennis/qbubble.gif" height="50" width="60"
alt="(?) " border="0">
Persistent Boot Sector
</H3>
<p><strong>From Hummingbird Designs on Thu, 24 Dec 1998
</strong></p>
<!-- ::
Persistent Boot Sector
~~~~~~~~~~~~~~~~~~~~~~
:: -->
<P><STRONG><IMG SRC="../../gx/dennis/qbub.gif" ALT="(?)"
HEIGHT="28" WIDTH="50" BORDER="0"
>
Hi,
</STRONG></P>
<P><STRONG>
I installed Linux on my PC at work and had everything working with
System commander, I have to use NT for some apps we use at work.
</STRONG></P>
<P><STRONG>
anyway, I was trying to get the nic card working so I tried using
the setup tool to install the kernel from the Cdrom that is used
to install linux off a network. Now everytime I turn on the
machine it gives me the screen as if I had installed a bootdsk
like when you first install Linux. I have done EVERYTHING I know
of to get that out of there . . .I used a zerofill utility that
goes over each and every sector of every track and fills it with
0's including the MBR. and that damn message still comes up
everytime I boot. . . I was thinking of removing my Hard drive
and seeing if it flashed my BIOS or something cause according to
Quantum9its a quantum drive) their utility is almost like a low
level format.
</STRONG></P>
<P><STRONG>
</STRONG></P>
<BLOCKQUOTE><IMG SRC="../../gx/dennis/bbub.gif" alt="(!)"
HEIGHT="28" WIDTH="50" BORDER="0"
>
"the setup tool..." (what setup tool?)
"the screen as if I had installed a bootdsk[sic]" (what
screen?)
"EVERYTHING" (what is "everything?").
"zerofill utility" (what utility?)
"that damn message" (what damn message?).
</BLOCKQUOTE>
<BLOCKQUOTE>
You do seem to be a bit sketchy on the specifics so I'll
have to guess.
</BLOCKQUOTE>
<BLOCKQUOTE>
You had (some distribution of) Linux installed on your
system in a dual boot configuration with NT. You were using
System Commander as your primary boot manager. Presumably
you installed LILO (the Linux loader) into the "logical boot
record" (the "superblock") of one of your Linux filesystems
(presumably the root fs). While trying to configure or
troubleshoot some problem with a network card (NIC) you used
some sort of "setup" utility which somehow configured your
system to bypass System Commander's boot record (presumably
by overwriting it with a copy of LILO). You've tried some
ways to restore your System Commander installation, and/or
to build a new MBR, and those have been unsuccessful.
</BLOCKQUOTE>
<BLOCKQUOTE>
O.K. Given that guess work I have a hypothesis. You may
have run something like '<TT>FDISK /MBR</TT>' from your NT boot disk.
This may have enabled the active partition in your MBR. The
DOS MBR code would load the logical boot record of the
active partition. If your Linux partition (with its copy
of LILO in the superblock" ) just happened to be the active
partition at the time --- you might see that copy of LILO
(one of two that had been installed on your disk, one on the
MBR and the other in the LBR/superblock) as the first screen
on boot up.
</BLOCKQUOTE>
<BLOCKQUOTE>
(I'm not sure this scenario accounts for all of your
symptoms since this is all based on guesswork).
</BLOCKQUOTE>
<BLOCKQUOTE>
I have no idea what your "zero fill" utility is doing ---
but it almost certainly is not zero'ing out track zero of
your hard drive (including the MBR). That would render the
system unbootable and would destroy the primary copy of your
partition table (the last 50 bytes or so of the MBR). The
Linux/Unix command to do this is very simple:
</BLOCKQUOTE>
<BLOCKQUOTE> <BLOCKQUOTE> <CODE>
dd if=/dev/zero of=/dev/hda bs=512 count=63
</CODE> </BLOCKQUOTE> </BLOCKQUOTE>
<BLOCKQUOTE>
... where <TT>/dev/hda</TT> is the first IDE drive, 512 is the bytes
per sector and count is the number of sectors in a typical
track. DON'T DO THIS! (If you insist on doing this, first
double check which device you want to use, the first IDE is
<TT>/dev/hda</TT> and the first SCSI is <TT>/dev/sda</TT>, then check the
number of sectors per track --- which should be listed in
your CMOS setup for an IDE drive and would be listed in your
vendor documentation and <EM>possibly</EM> by your SCSI adapter
diagnostics firmware).
</BLOCKQUOTE>
<BLOCKQUOTE>
You could save a copy of your MBR and partition table using
dd with a command like:
</BLOCKQUOTE>
<BLOCKQUOTE> <BLOCKQUOTE> <CODE>
dd if=/dev/hda bs=512 count=1 of=/root/mbr.bin
</CODE> </BLOCKQUOTE> </BLOCKQUOTE>
<BLOCKQUOTE>
... which you can use in scripts to compare and replace your
MBR in future mishaps.
</BLOCKQUOTE>
<BLOCKQUOTE>
It's possible that System Commander's boot loader is still
in the MBR --- but that it's been configured to skip it's
opening menu/selection prompting and boot directly off of
your Linux partition.
</BLOCKQUOTE>
<BLOCKQUOTE>
Of course it's also possible that Linux as completely
taken over your system; that's it's run amok and overwritten
every partition and drive on the system. In my experience
that would only happen if you (or someone) <EM>told</EM> it do
do this. I've never seen Linux touch any part of a hard
drive unless it was "told" to do so. (Unlike MS-DOS,
OS/2, and Windows which periodically trash the MBR when
they hang --- apparently scribbling register or random
memory contents over track zero, sector zero when those
zero's just happen to be in the the register during the
dying spasms of those systems).
</BLOCKQUOTE>
<BLOCKQUOTE>
There is virtually no chance that Linux touched your flash
BIOS --- so this is not a bug in your firmware. I'd say
that this "zerofill" utility is highly suspect. Obviously
Linux users just use the 'dd' command for this sort of
thing.
</BLOCKQUOTE>
<BLOCKQUOTE>
As for how to fix you problem. You could try re-installing
System Commander. I've never used it --- but it seems
that it can find most types of partitions during
installation --- so it should be able to find your NT and
Linux filesystems and install a new copy of it's boot loader
code to start either of these systems. I've never used
System Commander --- but it is commercial software --- so
it <EM>SHOULD</EM> come with some technical support. Perhaps they
can walk you through the re-installation.
</BLOCKQUOTE>
<BLOCKQUOTE>
Keep in mind that LILO can still be installed on your MBR,
your superblock, or <EM>both</EM>, so it might still show up after
you have System Commander or NT's boot manager installed.
It should then only come up <EM>after</EM> you've selected an
option from your primary boot loader. This can be a
bit confusing --- so you can reconfigure lilo to
bypass any prompts or delays when you're calling it
in this fashion.
</BLOCKQUOTE>
<BLOCKQUOTE>
Keep in mind that you can also find, download, and
install LOADLIN.EXE into a DOS directory somewhere on
your system. You can use that instead of LILO (it's a
DOS program that loads linux kernels). I've heard a
rumor that there is an NT native console application
(an NT .EXE that you'd run under a CMD.EXE shell) to
load Linux. I've never seen it.
</BLOCKQUOTE>
<BLOCKQUOTE>
If you end up having to re-install Linux and NT (probably
unnecessary --- but it might be the easiest way) you
can configure Linux to boot from floppy and never touch the
boot records on your hard disk. It's also possible to
configure Linux to use some other hard disk on your system
--- and not have it touch your primary drive at all.
</BLOCKQUOTE>
<BLOCKQUOTE>
Read through back issues of this column and go through the
various multi-boot HOWTO's and mini-HOWTO's at the LDP site
(<A HREF="http://metalab.unc.edu/LDP">http://metalab.unc.edu/LDP</A>)
and it's mirrors. There are many options.
</BLOCKQUOTE>
<P><STRONG><IMG SRC="../../gx/dennis/qbub.gif" ALT="(?)"
HEIGHT="28" WIDTH="50" BORDER="0"
>
C's from home and a nic card I know to install linux over the
network and see if that gets rif of it.
</STRONG></P>
<BLOCKQUOTE><IMG SRC="../../gx/dennis/bbub.gif" alt="(!)"
HEIGHT="28" WIDTH="50" BORDER="0"
>
I don't get this at all. How would you expect
installing Linux (over a network or otherwise) to <em>get
rid of</em> a Linux boot loader.
</BLOCKQUOTE>
<P><STRONG><IMG SRC="../../gx/dennis/qbub.gif" ALT="(?)"
HEIGHT="28" WIDTH="50" BORDER="0"
>
any help would be appreciated
<br>Brian Korsund
</STRONG></P>
<!-- sig -->
<!-- end 79 -->
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<P> <hr> <P>
<H5 align="center"><a href="http://www.linuxgazette.com/ssc.copying.html"
>Copyright ©</a> 1999, James T. Dennis
<BR>Published in <I>The Linux Gazette</I> Issue 36 January 1999</H5>
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