Boot sector woes
Tom Joyce
network. I turn off the power and replace the case. The bloody thing
refuses to boot (Disk Boot Failure)... I try and reinstall NT, as the only
boot disks I have are Setup disks - no joy. The PC knows it has a HDD,
knows things about the HDD but can't seem to do anything to the bloody
thing. There appears to be a boot sector problem. Doh!
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Richard Skeen
: There's me, merrily upgrading a PC, it's working fine and back on the
: network. I turn off the power and replace the case. The bloody thing
: refuses to boot (Disk Boot Failure)... I try and reinstall NT, as the only
: boot disks I have are Setup disks - no joy. The PC knows it has a HDD,
: knows things about the HDD but can't seem to do anything to the bloody
: thing. There appears to be a boot sector problem. Doh!
If the boot sector is the problem, and you've got a DOS boot floppy, you
can always boot from that and do "fdisk /mbr" to re-write the HD's boot
record. I don't know if this will upset NT's boot loader though, having
only done this sort of thing on Win95 systems...
Rich.
Christopher Stokoe
> If the boot sector is the problem, and you've got a DOS boot floppy, you
> can always boot from that and do "fdisk /mbr" to re-write the HD's boot
> record. I don't know if this will upset NT's boot loader though, having
> only done this sort of thing on Win95 systems...
fdisk /mbr *does not* re-write the boot sector it formats it leaving your
hardisk as a "NON SYSTEM DISK". If you do choose this option you-ll have
to reinstall the NT boot loader / MBR.
Chris
Iain Georgeson
<ch...@young-jedi.demon.co.uk> writes
>Richard Skeen <ri...@durge.org> wrote:
>> If the boot sector is the problem, and you've got a DOS boot floppy, you
>> can always boot from that and do "fdisk /mbr" to re-write the HD's boot
>> record. I don't know if this will upset NT's boot loader though, having
>> only done this sort of thing on Win95 systems...
>fdisk /mbr *does not* re-write the boot sector it formats it leaving your
>hardisk as a "NON SYSTEM DISK". If you do choose this option you-ll have
>to reinstall the NT boot loader / MBR.
Luckily, Chris is talking a load of old cobblers here - fdisk /mbr
writes a bootloader into your MBR that boots the "active" partition,
which is fine for DoS and derivatives, and LILO if it's on a partition
superblock. It /will/ nuke NT's loader, but that's because NT is all
elbows when it comes to booting. It /doesn't/ lose your partition table,
or anything scary.
However... Repairing NT's booting chain is non-trivial. When I nuked
/my/ NT loader, it stayed nuked until I got a new disk and reinstalled
from scratch. The boot disks (you need /three/ just to boot enough bare-
bones NT to start rescuing it, plus an extra emergency rescue disk
(which you all made when you installed it, didn't you?)) have a "fix
bootsector" option. Sadly, it either cheerfully claimed to fix it while
having done nothing, or BSoDed halfway through the boot. Amazing.
Iain.
Darren Edmundson
Christopher Stokoe wrote:
> fdisk /mbr *does not* re-write the boot sector it formats it leaving your
> hardisk as a "NON SYSTEM DISK". If you do choose this option you-ll have
> to reinstall the NT boot loader / MBR.
fdisk *does not* format the MBR, that would be completely useless, the
MBR switch is used to recover the MBR so that the machine boots from the
first active partition. Least thats what happened last time I used it.
Of course, whether or not a dos MBR will work with NTLoader is unlikely,
remember we're talking about two microsoft products here. My first plan
of action would be to put lilo on the MBR and get that to boot the NT
partition....
Apologies for any odd formatting, I'm using NS on puppy for the first
time...
- D
Richard Skeen
: fdisk /mbr *does not* re-write the boot sector it formats it leaving your
: hardisk as a "NON SYSTEM DISK". If you do choose this option you-ll have
: to reinstall the NT boot loader / MBR.
Quite probably. But Tom originally said he _was_ trying to reinstall NT,
but it "couldn't seem to do anything" to the HD as there appeared to be
"a boot sector problem". My reasoning was that wiping the MBR would
enable the NT installer to re-write it, since it was refusing to at the
moment. Although you're right that since he's reinstalling from scratch,
what I wrote about upsetting NT's boot loader is irrelevent.
My only experience of this is from a load of machines I used to admin
which had a number of different OSs all installed on the same HD, using
System Commander to switch between them. Occasionally we'd manage to
trash the boot sector completely (ISTR this would sometimes happen
during installs of Beta versions of Win98), and an fdisk /mbr would be
the only way of cleaning things up enough to reinstall System Commander
on the boot sector.
Rich.
Chris Stokoe
: Christopher Stokoe wrote:
:> fdisk /mbr *does not* re-write the boot sector it formats it leaving your
:Darren Wrote:
:> fdisk *does not* format the MBR, that would be completely useless, the
Fdisk *does* format the mbr :-
"Fdisk /mbr is an undocumented support feature that can be used to wipe
the Master boot record while leaving the partition table intact. The
first 446 bytes are filled with 0's while the upper areas af the MBR
(446-512) are left unaltered" [1]
Now if you dont describe track writing '0' over the first 446 bytes of the
MBR formatting it then .... Ill obviously have to bow down before your
incredibly semantic based argument.
At no point does fdisk /mbr install a new bootrecord and to all intents
the bootrecord is blank.
All IMHO of course that and the MS Developers guide but hey
Chris.
[1] All from the marvelose prose contained within.....
MS Developer and Support Guide.
Iain Georgeson
writes
>Darren Edmundson <pu...@at.dot.durge.org> wrote:
>: Christopher Stokoe wrote:
>:> fdisk /mbr *does not* re-write the boot sector it formats it leaving your
>:Darren Wrote:
>:> fdisk *does not* format the MBR, that would be completely useless, the
>
>Fdisk *does* format the mbr :-
[Documentation for an undocumented feature, acknowledging it as such
*LOL*]
>Now if you dont describe track writing '0' over the first 446 bytes of the
>MBR formatting it then .... Ill obviously have to bow down before your
>incredibly semantic based argument.
Um, here you're trusting MS documentation over our personal experience.
>At no point does fdisk /mbr install a new bootrecord and to all intents
>the bootrecord is blank.
Wrong. Just ... wrong. Sorry, you're wrong. Use Linux.
>All IMHO of course that and the MS Developers guide but hey
^^^^^^^^^^^^^^^^^^^
Quite.
>[1] All from the marvelose prose contained within.....
Iain.
Stuart
> Of course, whether or not a dos MBR will work with NTLoader is unlikely,
> remember we're talking about two microsoft products here. My first plan
> of action would be to put lilo on the MBR and get that to boot the NT
> partition....
AFAIR lilo can't boot an NT bootsector. At least, the version of lilo I
was using appeared to have no facilities for copying and executing a
second bootsector.
If you know a way of making it work I'd be very interested.
Stuart.
Richard Skeen
:
: AFAIR lilo can't boot an NT bootsector. At least, the version of lilo I
: was using appeared to have no facilities for copying and executing a
: second bootsector.
I could be wrong, but my understanding was that different partitions can
each have their own boot sectors. So the boot sector for Windows would
be on the windows partition, etc. Which is why it's possibly to use LILO
to dual boot a system - LILO lives on the MBR and can be told to boot a
specific partition [1] rather than loading Linux or whatever. Just like
the normal MBR would boot from that partition. There's no copying
involved. Although, as I say, I might have misunderstood...
Rich.
[1] E.g. in lilo.conf "boot=/dev/hda" - tells lilo which hard disk to
write the new MBR to, and an entry like "other=/dev/hda2" tells lilo a
specific partition to boot Windows from.
Chris Stokoe
: In article <75qci5$645$1...@fof2.durge.org>, Chris Stokoe <ch...@durge.org>
: writes
: [Documentation for an undocumented feature, acknowledging it as such
: *LOL*]
Undocumented for the lusers guides but i think you'll find the support
guides contain a full description of FDISK and many other "undocumented"
features. Including the infamouse ASCII coded directories etc etc
:>Now if you dont describe track writing '0' over the first 446 bytes of the
:>MBR formatting it then .... Ill obviously have to bow down before your
:>incredibly semantic based argument.
: Um, here you're trusting MS documentation over our personal experience.
Well they created the software and your being ignorant if you dont at
least read it. So altogether now RTFM.
:>At no point does fdisk /mbr install a new bootrecord and to all intents
:>the bootrecord is blank.
: Wrong. Just ... wrong. Sorry, you're wrong. Use Linux.
Right just Right if you give me 10 seconds with your linux machine and a
dos bootdisk i would *prove* this is how it works
*sigh*
Chris
Darren Edmundson
> Well they created the software and your being ignorant if you dont at
> least read it. So altogether now RTFM.
Well I could be a complete twat and point out that Microsoft *bought*
DOS when IBM came to them and asked them for an OS and Language - they
already had BASIC, but no OS, so they didn't actually create it, they
just extended it, and like everything since they screwed it up. Dos 4.x
anyone?
- D
Darren Edmundson
> "Fdisk /mbr is an undocumented support feature that can be used to wipe
> the Master boot record while leaving the partition table intact. The
> first 446 bytes are filled with 0's while the upper areas af the MBR
> (446-512) are left unaltered" [1]
Um, well that may well be what MS think it does, but last time I
checked, the MBR was the sector that was loaded at boot-time and run in
order to boot whichever active partitions are listed in the partition
table (also in this same sector). As such this area contains executable
code, and since 0000000000... is not meaningful 8086 code, it kinda
precludes FDISK /MBR filling it with 0's from being useful...
FYI (from the antivirus newsgroups - do a DJN search for "FDISK MRB
EXECUTABLE")
fdisk /MBR repairs a damaged (or infected) master boot record by
over-writing it with the standard DOS MBR. There is a single situation
where fdisk would clear it - if the partition table itself was invalid
(didn't have the majik cookie at the end).
Remeber, due to legal reasons, many departments of Microsoft are
prevented from freely sharing information with each other. Obviously the
undocumented documentation that you dug up was written by someone who
didn't have access to information about the OS code :)
- Darren has resorted to "dd if="/dev/zero" of="/dev/hda"... before,
after NTLoader tried to be helpful...
dar...@at.dot.durge.org
> AFAIR lilo can't boot an NT bootsector. At least, the version of lilo I
> was using appeared to have no facilities for copying and executing a
> second bootsector.
Um, Last time I tried I had no problems (IIRC), Lilo on the MBR, and
NTLoader on the partion's Boot Sector - BS code is pretty standard, load
512 bytes at 0000:7C00 and JMP to it...
YMMV.
- D
Iain Georgeson
<stu...@orfe.demon.co.uk> writes
>AFAIR lilo can't boot an NT bootsector. At least, the version of lilo I
>was using appeared to have no facilities for copying and executing a
>second bootsector.
Not sure why you want to copy it. dd will, if you ask nicely, though.
>If you know a way of making it work I'd be very interested.
I believe, although I haven't tried it, you can if your NT partition is
the first one on the disk - that way it keeps all its bootloader crap on
its own partition instead of dumping it on a convenient DOS partition,
and you can do the tradition partition bootsector thing. Perhaps someone
who's tried it could pipe up?
All in all, it means re-installing. I wouldn't bother.
Iain.
s...@remove.drogna.spam.force9.co.uk
> In article <t5vr57...@big-switch.orfe.demon.co.uk>, Stuart
> <stu...@orfe.demon.co.uk> writes
>>AFAIR lilo can't boot an NT bootsector. At least, the version of lilo I
>>was using appeared to have no facilities for copying and executing a
>>second bootsector.
> Not sure why you want to copy it. dd will, if you ask nicely, though.
>>If you know a way of making it work I'd be very interested.
> I believe, although I haven't tried it, you can if your NT partition is
> the first one on the disk - that way it keeps all its bootloader crap on
> its own partition instead of dumping it on a convenient DOS partition,
> and you can do the tradition partition bootsector thing. Perhaps someone
> who's tried it could pipe up?
That would explain why I could never get lilo to work when I had NT. I
resorted to getting lilo to dump to a file on my C drive, and then using
NT bootloader to start that.
Stu hopes theres a new 2.2 prepatch to compile today ;)