Booting from a USB Drive

[Steve Holmes]

On Mon, Dec 06, 2010 at 04:27:21PM -0700, Matt Graham wrote:
> Does your initrd/ramfs/whatever have the ehci_hcd, scsi_mod, sd_mod, usbcore,
> and usb_storage modules available in it?  Are those modules loaded?  If this
> thing was always going to run from a USB drive and I had control over the
> kernel, I'd build a custom kernel with all those things built-in, not as
> modules, to avoid that particular set of problems.  (BTDT back in 1999, but
> with ELF binary support as <M>, seriously, so the kernel loaded but /sbin/init
> couldn't execute.  Sigh.  It was a great learning experience.)

Good question.  I think so but will have to examine my initcpio
package and see if everything is intact; when I looked at the conf
file for it, I thought it pretty much listed everything.  But I wasn't
all that thurough either.

> This is a totally different problem, and it doesn't totally jive with what you
> wrote above ("/dev/sdb wasn't even mentioned").  If it can see the USB drive,
> but it can't see the partitions on the drive, then the drive may have been put
> together with a non-x86 partition layout.  In that case, you have to build the
> kernel with support for whatever partition layout's on the drive.  There are a
> bunch of them.  GPT, OS X, whatever, they can all be used for a Linux system. 
> The x86 BIOS only groks a couple of them though.

The inconsistendy here is with some prior tests, /dev/sdb was
mentioned like in the first few lines of messages pertaining to
available devices; you would usually see first mention of sdb and then
a line or two later, sdb1, sdb2, etc.  Today when I tested this stuff,
/dev/sdb didn't come up at all unless it was in an earlier message
that scrolled off screen.  In all cases, the items in /dev/disk do not
show anything linked to /dev/sdb anything.  I have an idea that if the
system could properly locate the /dev/sdb partitions, I would be much
further on my way.

I used cfdisk to format two partitions: #1 for linux (83) and #2 for
linux swap (82). I had the Arch Linux installer build the ext3
filesystem and standard swap system for the other partitions.  When
booted from a live CD, I can mount this drive perfectly and see all my
files on that portable drive.