[conspire] Help with GRUB
paulz at ieee.org
Thu Nov 5 12:05:24 PST 2009
Thanks for detailed advise. Some specific replies are below.
>Quoting Paul Zander
(paulz at ieee.org):
>> So, from rescue CD, grub find
/boot/stage1 returns (hd0,4)
>> That matches with knowing
that it is also on sda5.
>Do I correctly assume that this
means you have an MS-Windows
>installation on /dev/sda1 and a
Linux installation on /dev/sda5?
YES, that is correct.
>> So I gave the commands:
and rebooted the machine w/o the CD.
>And it worked, right?
I'm unclear, from your description. At the
>point where you
typed "quit", above, that merely took you back to the
prompt where you _could_ have then typed "b" to boot using
>revised, manually-entered directives you specified above.
Did you do
>(Late addition, written after
the section that follows: Actually, at
>that point you didn't
have quite enough. You haven't (at that point)
where to find a kernel and what root filesystem it should
at boot time. So, I'm inferring that you never tried "b".
>"setup(hd0,4)" writes persistent bootable
information to the superblock
>of /dev/sda5, a point I'll
return to, below.)
I'm still in the steep part of the
learning curve on grub. Knowing about “b”,
would have been a useful thing.
of the point of doing entry of commands manually at the GRUB
>is to validate your understanding of where everything
is, phrased in
>GRUB-speak, so that you can (if necessary)
correct the contents of a
>copy of menu.lst prior to running
grub-install, which implements those
>contents as instructions,
and writes bootable information to wherever
>you said in
menu.lst to put it.
-- much IMPORTANT info about MBR
skipped for further study
>> once the grub
menu appeared, I gave "c" for command,
>> and it returns (hd2,4)
so GRUB found a GRUB "stage1" file on the fifth partition
>logical partition) of one of your secondary hard
>> The confusion between sda and sdc would be
enough to explain the wrong
>> partition types.
not sure what you mean when you say "the confusion" --
>I do remember your account of boot failures
>partition types. Whose confusion,
though? One of the unanswered
>questions, IIRC, is what on
Earth happened to your system. It seems
>reasonable to suppose
that either there was some substantive hardware
insertion or removal of hard drives, rejumpering, etc., or
you or some piece of hardware operating on your behalf attempted to
>rewrite your bootloader setup and got wrong the
For openers, I was certainly confused.
Now I know that sda, sdb, etc are
defined by the hardware connections.
However hd0 does not always map to sda.
>It _might_ be useful to attempt
to retrace what happened -- or,
>alternatively, you could
decide you'd rather just concentrate on fixing
>the setup and
deliberately disregard the question of how it got that
Either choice could be defensible.
>Anyhow, it's your
hardware, i.e., you can see right in front of you what
and do not have, which is a big advantage you have over the rest
us. Presumably, you know where MS-Windows is -- probably
>Presumably, you know how many hard drives you have
and where Linux is --
>maybe (hd0,4) aka /dev/sda5. So, how
about you use that knowledge and
>see if you can make GRUB do
what you want?
>Backing up a bit, a large part of the
rationale for _first_ doing a
>manually-driven boot from the
GRUB command line is to test your
>understanding of where
everything is in GRUB-speak, _before_ fooling
contents of menu.lst. You can test
> grub> root
> grub> kernel /vmlinuz root=/dev/sda5
...all day long without writing any
persistent information anywhere.
directive, by contrast, says "Write first-stage
information to _here_". So, it does create a persistent
>That wrote first-stage bootloader information
to /dev/sda5's superblock.
>Which leaves me wondering, how were
you expecting GRUB to branch to
>there? What do you have in the
>Anyway, to answer your question, you should test your
ability to boot
>MS-Windows and Linux entirely from the grub
command line manually.
>Then, armed with that confirmed
knowledge of where your OS filesystems
>and other essential
objects are, start up Linux and revise
match reality. Then, do "grub-install [something]"
make /sbin/grub write bootable stuff somewhere. The [something]
>could be "(hd0)" if you want to make /sbin/grub
write to the MBR, for
command from the GRUB command line:
At this point, I can get grub to boot
debian from the hard drive by
modifying menu.lst to read (hd2,4).
From the above, I now understand
that there are possibly cleaner fixes
to my work-around. I will experiment
However I have not been able to get
windows to boot. Most likely
that install was not correct. What I
know is that I took computer to
have windows re-installed after it got
some serious malware.
I told the installer it was OK to
over-write the MBR. He said he
did the first part of the install. He
rebooted and windows started
as he expected. Then he installed
“some drivers”. After that, grub
re-appeared and he could not boot and
So, I am going to
1. re-read and experiment with grub
I have a better understanding of what
is going on.
2. Then I will look more closely at
Rick's comments about MBR and
figure out how to make that a non-issue
so I can return to the
3. Expect to re-install grub because
MS will mess with the MBR.
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