Kernel panic when booting off USB flash drive

[galapogos]

Hi,

I have a custom linux environment with a 2.6 kernel downloaded from kernel.org with a simple busybox shell as init. The system boots off a SATA drive with root=/dev/sda with lilo, and it works perfectly.

I recently tried to achieve the same thing on a USB flash drive by simply dd-ing the SATA drive partition contents to the flash drive, but I'm getting the following error when booting up:

VFS: Cannot open root device "801" or unknown-block(8,1)
Please append a correct "root=" boot option; here are the available partitions:
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(8,1)
Pid: 1, comm: swapper not tainted 2.6.35.14 #1

I only have a single flash drive plugged into the USB port, with no other SATA/IDE drives connected. AFAIK, that makes the flash drive /dev/sda, which translates to 801, so why isn't it booting up correctly?

Thanks.

[yancek]

If you only copied the partition contents to the flash, what are you using to boot that gives you the message as you don't indicate a bootloader in the mbr of the flash?
You might boot a Live CD when you only have the flash attached to see if it actually is seen as sda.

[oz]

Good day, galpogos

After reading your post, my first thought was no bootloader on the MBR, just as mentioned above by yancek. Did your dd command include a write to the MBR, or did you install lilo to the MBR of the USB drive using a separate command?

[galapogos]

Good day, galpogos

After reading your post, my first thought was no bootloader on the MBR, just as mentioned above by yancek. Did your dd command include a write to the MBR, or did you install lilo to the MBR of the USB drive using a separate command?

Thanks for the replies.

I dd-ed the entire disk image over, from the 1st sector onwards which should include the MBR. Obviously the flash disk being much smaller than my SATA drive, I didn't dd the irrelevant portions at the end of the disk. The entire disk image is only 64MB, which consists of a few small partitions. However the MBR should nevertheless be there.

I have previously used the same method to dd the disk image over to several other SATA drives, and they've all booted up perfectly, so I doubt it's a MBR problem, otherwise these SATA drives would exhibit the same behavior wouldn't they?

[oz]

Some flash drives have hidden security partitions on them, so maybe such a partition changed the partition numbering on your device. I don't remember at what point the kernel changed partitions from hda to sda, but it could be related to that I suppose since you are dealing with a 2.6 kernel. Just throwing some ideas out there.

Are you able to plug it into a working system and list the partitions with fdisk? If no, maybe boot a liveCD and look at the partitions using gparted. Don't know if it will help...

[galapogos]

The move from hda to sda coincided with the move from IDE to SATA, which was very long ago. I believe it was the very early 2.6 builds. I'm using a kernel that has explicit support for SATA drives and has worked with it, so that can't be the problem.

Thanks though.

[fenario]

hi galapogos

you may want to try using unetbootin. the one from the synaptic repos doesn't always work but the standalone linux file from the unetbootin site always works fine.

fen