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Old 11-03-2004, 06:05 AM   #1
arturo63
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why doesn't grub see my IDE cd devices?


I've posted sthg like this in another thread concerning Win-Linux multi boot, but
I feel it's better to post it as a new subject. Sorry if this is not a correct policy.

What I need is a GRUB-managed boot from CD because I have to map the drives in order to "cheat" windows about where to write its MBR.
It looks that GRUB only recognises my SCSI devices (actually, they are 2 HD under SATARaid controller, with Raid function disable):
(hd0)=>/dev/sda
(hd1)=>/dev/sdb
(fd0)=>/dev/fd0
while I could not find a way to "introduce" to GRUB either /dev/hdc or /dev/hdd that are the (IDE ?) CDrom drives.
no mention on this in GRUB documentation or web page,
I've found something on linuxforums.org, but the case mentioned there concerns only IDE devices.
Should I change anything in the BIOS?

TIA
N.
 
Old 11-03-2004, 07:13 AM   #2
Wordan
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Did you try adding the CD drive to the boot order in your bios? Im not sure if that makes a difference.
 
Old 11-03-2004, 08:27 AM   #3
michaelk
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Here are instructions for creating a grub boot CD.
http://www.gnu.org/software/grub/man...le-CD-ROM.html

I don't think you can "cheat" windows from writing to the MBR which will be the hard disk designated in the BIOS for booting. AFAIK CDROM drives do not get mapped like hard disk drives and therefore can not be included in grub's device map. Once the BIOS passes booting off to the hard drive I do not think you can then select a CDROM device.
 
Old 11-03-2004, 10:04 AM   #4
arturo63
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Quote:
Originally posted by michaelk
Here are instructions for creating a grub boot CD.
http://www.gnu.org/software/grub/man...le-CD-ROM.html

I don't think you can "cheat" windows from writing to the MBR which will be the hard disk designated in the BIOS for booting. AFAIK CDROM drives do not get mapped like hard disk drives and therefore can not be included in grub's device map. Once the BIOS passes booting off to the hard drive I do not think you can then select a CDROM device.
Hi!
well, windows cheating in writing MBR did work, indeed.
As I said in my first post, the background of this story is in another thread: http://www.linuxquestions.org/questi...hreadid=248415

The instructions for booting from a different MBR are

title XP
map (hd0) (hd1)
map (hd1) (hd0)
rootnoverify (hd1,0)
chainloader +1
where (hd1,0) is the first partition of the second HD of the chain.
similarly, if you wish to install XP (or other winz) if you only have linux, the instruction to boot from a winz installation floppy disks are:

title win floppy
map (hd0) (hd1)
map (hd1) (hd0)
rootnoverify (fd0)
chainloader +1


I've taken them from a HOWTO http://www.tldp.org/HOWTO/Linux+Win9x+Grub-HOWTO/
from which I understood that iwt would indeed be possible to use a bootable CD under GRUB. I quote:

> The "DOS boot disk" section is needed if you are going to boot from floppy to begin the Windows install,
> but it will also come in handy after your install if you ever want to use a DOS boot disk for whatever reason.
> If your Windows install CD is bootable, you'll need to have a "Windows boot disk" section which chainloads
> to whatever your CDROM device is called.

well, I cannot figure out what this whatever should be!!!!

As the instruction auto-completion on command-line grub also presents (fd0), (hd0) and (hd1), it sound reasonable what you say, that when BIOS gives GRUB the floor, there's no way to map the CD.
Nevertheless, in another thread I've found, an IDE chain with 2 hard disks and 2 CD drives is mapped by 4 entries like
(hd0)=/dev/hda
(hd1)=/dev/hdb
(hd2)=/dev/hdc
(hd3)=/dev/hdd

OK, these are all the clues I'm working on in order to find a way to use CD rom installations.

Any suggestions is warmly welcome.

Thanks
 
Old 11-03-2004, 12:09 PM   #5
michaelk
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As you said I misunderstood what you meant about cheating. However, drive mapping is not booting from a different MBR.

Here is the way I understand things. No matter what drive you boot from whether it is hda or hdc etc. the BIOS will map it hd0. The next drive found will be hd1 no matter if it is hdb, hdc or hdd. Because windows expects to be on the first recognized drive you need to use the drive mapping command.

By the way it is the same thing for partitions. hd0,0 is the first partition found on the first disk but it may not be /dev/hda1.

here is a good example in the following link on drive mapping. The same principle is true of IDE drives.
http://www.tldp.org/HOWTO/LILO-6.html

I know the BIOS also maps floppies but can't find the info at the moment. I disagree with some of the info in the link you posted. But then I could be mistaken too... Booting from a CD is not the same as booting from a hard drive.

The link I posted writes the stage 2 to CD so you couldn't change the menu.lst AFAIK. I've never tried doing this.

I'm out of ideas at the moment because I really do not understand what you really need.

Last edited by michaelk; 11-03-2004 at 12:19 PM.
 
Old 11-04-2004, 03:50 AM   #6
arturo63
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Quote:
Originally posted by michaelk
I really do not understand what you really need.
I'm sorry I was not able to explain the situation. I believe it's a matter of "newbie-ness" and poor technical english. I apologise for that.
another problem probably arises around the word "disk mapping", that as far as I understand, has a twofold meaning:
one concerning the name given by BIOS or GRUB to the devices, the second is the "cheating" procedure from within GRUB, a sort of "virtual disk swapping",
Well', I try to put it in other words:
When I turn the coputer on, and I have a bootable CD in, I get the message "press any key to boot from CD".
So, I understand that the CD drive is on the BIOS list of boot devices.
As a matter of facts, before understanding grub's functionalities, I tried to install XP from the CD just making it boot the computer as asked by BIOS.
It all ended up in windows asking me to format the first disk (where SUSE LINUX) is installed, because it does not find a known partition to write the MBR on.
What I had to do, was to use GRUB as I've described earlier.
This has to be made before booting, I understand, so that when win installation goes on, it finds a good parition already prepared in the secnd HD, now virtually mapped as first.
That's what i mean when I speak about "a grub-managed" boot.
Well, I could install XP only via floppy start disks, downloaded from microsoft. But, of course, the whole thing was lengthy and boring (6 floppys).
Now that I want to install XP-64bit edition, which most likely has not floppy start disks available (I still have to check microsoft site), I need to manage a boot from CD by GRUB.

Hope I was more clear, this time.
Thanks

N.
 
Old 11-04-2004, 02:09 PM   #7
michaelk
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I've never tried install windows to a second drive. I would think that if you changed the BIOS to select the 2nd drive as the boot device the installer would not use the 1st drive.

If you create windows partitions on the second drive then the installer might recognize them go on its way. No need to preformat them.
 
Old 11-09-2004, 09:24 AM   #8
arturo63
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Quote:
Originally posted by michaelk
I've never tried install windows to a second drive. I would think that if you changed the BIOS to select the 2nd drive as the boot device the installer would not use the 1st drive.

If you create windows partitions on the second drive then the installer might recognize them go on its way. No need to preformat them.
That's it!

I eventually succeeded in installing XP64bit!
It was indeed a matter of disk swapping,and as you suggest, it was possible to manage it from BIOS.
As The OS's are in two separate disks, I changed the boot order, leaving CD as first device, then the disk1, then disk0 then floppy.
This made the system boot with the Windows MBR.
What I did not expect (perhaps it was a trivial feature of BIOS that I ignored), is that in this way, the boot from the XP64 installation CD "kept memory" of the boot order, the MBR location was in this way OK for uncle bill's product ant the instalation was worked out fine.
Then I switched the boot order back to the original situation and I ended up with grub managing the boot, chainloading the two XP's, with the choice between them managed by the default windows bootloader in the second drive.
I was assuming that boot order in BIOS was only used to point to the boot device, not to map the devices in a "non temporary" way

Thanks again for the valuable suggestions

N
 
  


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