kubuntu vs fedora initrd init files

[Mikkel L. Ellertson]

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jackson byers wrote:
> Mikkel responded:
> To tell if Ubuntu does the same thing, you would have to do the same
> type of install. The reordering of the disks is because of two
> reasons. The first is because of the BIOS, and affects Grub. When
> you boot from a USB device, that device becomes BIOS drive 80, or
> Grub drive hd0. This is because what ever hard drive you boot from
> is automatically set to BIOS drive 80. This is also true when you
> tell the BIOS to boot from the second hard drive in the machine.
> 
> The other reason affects the kernel ordering. How the kernel assigns
> drives depends on the module loading order. Because you have to load
> the usb_storage module from the initrd, the USB drive is the first
> controller scanned. (There are ways to change that, but it not
> easy.) This affects any kernel, or distribution that uses modules.
> You run into the same thing when you install Ubuntu to a USB drive.
> That is why a USB install is only offered as an expert install.
> Mikkel
> ------------------
> Mikkel,
> thanks for response. As is often the case, your response if full of info.
> I am trying to absorb it all.
>> To tell if Ubuntu does the same thing, you would have to do the same
>> type of install.
> First, let's be sure we are on same page.
> What I did was to boot a usbexternaldisk copy of main fc5.
> (this was not an anaconda install to the usbdisk)
> I did this 2ways, each with its own grub.conf stanza
> 1) using  kernel,initrd from a kubuntu 6.06 dapper
>    this boots, disks are _not_ reordered   ie usb is seen as sdc
> 2) using the kernel,initrd of the fc5copy(same as in mainfc5)
>    this boots, disks _are_ reordered   ie usb is seen as sda
> 
> But, my bios does not see the usb disk, so in _both_ cases
>  I copied the /boot files from the fc5copy into  sdb3 = (hd1,2)
> This makes it  some kind of usb/scsi hybrid  bc the /boot files are on sdb
> 
OK - On the systems I use, they offer the option to boot from a USB
device. I have used this to boot from USB memory drives, as well as
 USB hard drives. I have done a complete new install to a USB hard
drive as well. In all cases, the BIOS did not list the drive as an
internal hard drive, but it was able to boot from it, and it became
BIOS device 80, and Grub device hd0.

> So when you say "have to do same type of install"
> I think you mean, make a usbdisk copy of the kubuntu install (now on sdb5)
> and then use the kubuntu kernel,initrd to boot this.
> Then, if this again results in disks _not_ reordered,
> only then will be able to see "if ubuntu does the same thing".
> Correct me if I am not understanding you.
> 
Yes, this is what I mean. When you build an initrd so that you mount
the USB drive as your / partition, it will also set that as /dev/sda.

> this will take some time, but I want to go thru with it.
> I first have to mv the fc5copy out of the topdir of the usb(its one
> large partn)
> and have my backup scripts do the copy of the kubuntu install to
> topdir of usb.
> 
> Jack
> 
I have done it both ways - as a fresh install, and by taking a hard
drive with an installed OS, and putting it in an external USB case,
and the drive has always ended up as /dev/sda. This  is much less of
a problem if you are using LVM and/of partition labels then if you
are mounting partitions directly. (As long as your LVM names do not
collide! ie more then one VolGroup00.)

By far, the easiest is to do a fresh, expert install to a USB drive
- it will even do the proper Grub install so that you can boot off
the USB drive directly on any system that supports booting from a
USB drive. You can do this when moving an install to an external
case, but it is much easier doing it at install time.

Mikkel
-- 

  Do not meddle in the affairs of dragons,
for thou art crunchy and taste good with Ketchup!

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