I have Ubuntu Breezy Badger 5.10 installed on an external USB HDD (40Gb) that I am able to boot successfully on my Desktop. This involved a bit of playing around, including:

• Install from CD
• Reboot into rescue mode
• Add "WAIT=12" to the top of initramfs.conf
• Add USB support modules to /etc/mkinitramfs/modules
• Create a script to get the machine to pause in /etc/mkinitramfs/scripts/init-premount
• Create the new initrd image with USB support
• Modify /boot/grub/menu.lst to recognise the new image and correct HD (0,0)

(Most of this came from a thread I found on ubuntuforums (thread 80811))

As I said, this works fine on my desktop, but when I try to boot from my Dell D610 laptop, it fails to boot saying that it can't find /dev/sdb1. This is the problem that I was having with the desktop, but I was able to fix it in the fifth point above.

I have tried the install process again using the laptop and it all works fine until I get to the reboot point, where it says it can't find /dev/sdb1. I'm sure this is the correct /dev mount point because the installation went to /dev/sdb1 and I installed grub to /dev/sdb.

It seems that this problem may be specific to the Dell D610, but it is years since I have had any in depth experience with Linux installations and I'm not sure if it is something that I am doing.

Can someone please help?

i think your laptop is seeing it as sda1, and your desktop is seeing it as sdb1.

I've been through and checked all possible combinations of hd(x,y) and /sdX in the grub boot commands, but none of them work. If I watch the verbose output of the boot sequence, it comes up recognising the hard drive as /dev/sdb but then it says it can't find /dev/sdb1

It seems like it is something strange with the Dell laptop, but now I am even more confused because after I plugged the HDD back into my desktop it isn't working on that anymore either. Are there some modules I need to load in the boot sequence? I have sd_mod, usb-storage, ehci, ohci, uhci...

OK, I think I've found the what is causing the problem, but it doesn't put me any closer to getting it sorted out.

Sometimes when I boot on my desktop, it comes up with a message saying "Attached scsi disk sdb at scsi 0, channel 0, id 0, lun 0". When this happens, I can boot successfully into Ubuntu off the USB HDD, but if it doesn't, I can't boot.

This message always appears on both machines: "SCSI device sdb: 78242976 512-byte hdwr seconds (40060 MB)". However the desktop sometimes then connects the device (as per the message above) but the laptop never does.

Could it be something to do with the modules I have loaded? I am going to try taking ehci-hcd out of the modules list and see if that helps.

ehci-hcd is only for usb 2.0.
Does your external hard drive use an A/C adapter?
If not you may try using a usb hub with thats self powered and is not powered off of the bus.