[CentOS] Installing CentOS 6.2 *TO* a USB drive, not installing from USB.

hd0,0 represents the bios device id, are you sure thats what your bios
thinks the usb disk is at ?

I can't be sure which is part of the problem. Because when I read the
grub documentation, it said that hitting tab at the prompt after
typing the command will produce a list of possible devices/drives.
However, in my case, nothing happens which seemingly implies grub
could not find any device.

I also did try manually doing (hd0,1), (hd1,0) but none of it seemed
to be a "findable" device. For what it's worth, the installer did see
them as sda and sdb. I also disabled the onboard SATA controller
during my attempts in order to eliminate it from showing up as a
possible device, since grub doc says the (hdx,x) number usually
matches the order in which the devices were discovered.

The grub order and names and the linux kernel/udev order and names should not be assumed to have any correlation of any kind, since they are discovered differently.

If you can boot a USB live media on this box, you could bring up a grub shell and see how grub sees the disks from that (at a root prompt, type 'grub' and you'll be greeted with the grub shell, and then you can do detection or whatever from that). This also works in the rescue environment given by the install media; you do want to do a 'chroot /mnt/sysimage' in that shell before entering the grub shell, though.

It is completely BIOS dependent as to how the devices show up to grub.

Yes, that is what I understand from the grub manual. However, from
that I also understand and expect the first and only device grub could
find would be hd0
I've done this previously from the rescue environment but got no
closer to resolving this.

I've tried it again with a default install of CentOS 6.2, using
default drive layout and all.
On first boot, I get the grub shell but I have not been able to find
any command that would list valid devices grub can find, apart from
the tab button.

Rebooting into the rescue environment, chrooting into the drive,
grub-install generates the map to hd(0) which was expected. Runing
grub shell and trying root (hd0) also works.

However, rebooting after updating the grub device map always results
in "Booting from local disk... Error 21" which indicates grub couldn't
find the drive specified.

Any ideas how I can probe/list devices within grub shell? I've done
the stupid method of root(hd0,x) all the way up to root(hd8,3) without
luck.

In trying to solve this problem, I came across these two articles
regarding GRUB and USB booting.

http://vlinux-freak.blogspot.com/2011/01/how-to-create-grub-boot-floppy-usb.html
http://bootloader.wikidot.com/linux:boot:usb-grub

The floppy drive issue appears to be the situation as booting the
rescue environment from a USB DVD does show up as /dev/fd0.

However, the solutions in those articles did not work. In the first,
the GRUB command/options are different, although changing the option
from boot-directory to root-directory appear to work, there was no
option to force floppy drive.

In the second, the python script thinks the grub install has already
been patched for floppy boot so couldn't do anything.

I've also tried editing menu.lst to use (fd0) but also didn't work.

Have you tried the grub "find" command?
find /grub/stage1
find /boot/grub/stage1
etc.

http://wiki.centos.org/TipsAndTricks/TroubleshootGRUB

Phil

Emmanuel,
I used a totally different approach by using VMware: the trick is to
install on a physical device which is the USB drive.
When the installation requests a reboot, simply boot on your USB and off
you go!

2012/4/10 Phil Schaffner <Philip.R.Schaffner at nasa.gov>

That is pretty much what I did. Boot DVD 1 with a USB DVD drive,
install to /dev/sda which is the USB flash drive. When the
installation requests a reboot, shutdown, remove as well as leave the
DVD drive around and reboot... and only grub prompt or Error 21.

Maybe there's a minor but critical step I'm missing so I'll appreciate
it if you could outline in greater details how you did it.

I've tried installing grub to both MBR i.e. /dev/sda as well as first
partition /dev/sda1 but neither works.

Two questions: a) are you sure that the USB key is /dev/sda, and b) does
your system offer a boot menu, or only go into setup to tell it to boot
off the USB key?

Oh, and in fdisk, is the partition flagged bootable?

mark

Yes, I've verified this before and again after you asked that it is
seen as /dev/sda, at least through the installation DVD. fdisk also
does not find a sdb/c/d if I try that.
Both, I can set the boot sequence in BIOS, which is currently to boot
USB first. And I can also hit F10 to choose.
Yes, definitely :D

Usuially, I simply use the default config for about everything; it worked
well every time...

I don't remember every detail... sorry for that

-----Original Message-----
From: centos-bounces at centos.org [mailto:centos-bounces at centos.org] On Behalf
Of Emmanuel Noobadmin
Sent: mardi 10 avril 2012 17:32
To: CentOS mailing list
Subject: Re: [CentOS] Installing CentOS 6.2 *TO* a USB drive, not installing
from USB.
That is pretty much what I did. Boot DVD 1 with a USB DVD drive, install to
/dev/sda which is the USB flash drive. When the installation requests a
reboot, shutdown, remove as well as leave the DVD drive around and reboot...
and only grub prompt or Error 21.

Maybe there's a minor but critical step I'm missing so I'll appreciate it if
you could outline in greater details how you did it.

I've tried installing grub to both MBR i.e. /dev/sda as well as first
partition /dev/sda1 but neither works.
_______________________________________________
CentOS mailing list
CentOS at centos.org
http://lists.centos.org/mailman/listinfo/centos

I'm deeply embarrassed and stunned by why I did not stumble across
that googling or how I could miss seeing the command in grub shell and
doc. I'll try this the next time I get to that machine again.

Thank you very much!

I've tried that now but it could not find any of the files be it
stage1, grub.conf or menu.lst, also tried both /grub and /boot/grub
variants.

The interesting thing is that if I leave the DVD in the DVDROM drive,
grub will find it as hd111 with the tab button. So the tab
functionality is actually working. Just that as far as grub is
concerned, the flash drive it just loaded from just seem to be
undetectable.

On a random hunch or sheer desperation, I inserted an old brandless
1GB USB thumbdrive, installed and it booted.

Thinking that the Sandisk Ultra Backup 16GB was incompatible with
CentOS/grub for some unknown reason. I switched to a brandless 16GB,
installed the same way and it failed at grub prompt again.

Now it is starting to look as if either the newer drives have
something on them that prevents booting. Or it's the total size of the
drive, regardless of the partition size. I say this because in every
case I used a single 1GB ext4 / partition for testing, to reduce the
mkfs time.

Since now I have a bootable drive, I started to compare them with
fdisk to see if there was any difference.

Bootable
255 heads, 63 sectors/track, 124 cylinders, start sector 63
With a warning that
"Partition 1 has different physical/logical endings:
phys=(123, 254, 63) logical=(124, 140, 16)"

Unbootable 16GB Sandisk Ultra Backup
54 heads, 48 sectors/track, 12158 cylinders, start sector 2048

Unbootable 8GB Sandisk Blade
20 heads, 4 sectors/track, 195417 cylinders, start sector 2048

Unbootable 16GB Unbranded
171 heads, 40 sectors/track, 4634 cylinders, start sector 2048

It seems that the common issue is starting at sector 2048 so I fdisk
the 16GB Sandisk to manually create a 1GB partition started at sector
63. Using this, I installed and was able to boot successfully.

To verify, I use the same 16GB disk to install again, deleting the
partition in anaconda and creating a new 1GB partition, ctrl-alt-f2
and fdisk confirms it was again at sector 2048.

As a side note, for some reason, drive geometry changed for the 16GB
after a reinsert to varying values such as
6 heads, 33 sectors/track, 159164 cylinders
16 heads, 32 sectors/track, 61551 cylinders

Not sure if this had any significance to why anaconda decides to fdisk
the drive starting from sector 2048.

My only guess is that it considers anything bigger than 4GB as a
normal HDD drive and does this for hard disk alignment issue? But if
grub could boot normally from such a HDD, why would it choke on a USB
flash drive?

Should I report this as a bug with anaconda or ?

Wonder if it's trying to beat the rush - after weeks of googling, a few
weeks ago, I finally found that if I formatted my 3TB drives on a 4k
boundry, instead of a 512byte boundry, writes were literally about four
times faster, because that's the physical sector on the drives.

It may be trying to do the same, to take care of this invisibly.

Good catch on the USB drive business.

mark

That is what I think the 2K first sector is supposed to do, align the
physical sector be it a 512 or 4K drive. But unfortunately, the check
for "is this a 4K HDD" appears to be naive.