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Old 11-29-2008, 09:17 PM   #1
Registered: Jul 2005
Distribution: Arch Linux / Debian Etch (soon) / have tried many others
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Using Flash Drive as Root FS at Boot Time Fails

Okay, I'm sure there's something obvious here that I'm missing, but I can't seem to find how this should be done.
I have a flash drive that I want to mount as my root filesystem at boot time. When I'm in linux, I can run `mount /dev/sda1 /mnt`, and the kernel will mount the ext3 FS on the flash drive at /mnt with no problems.
From this I assumed I could boot my system with the kernel option 'root=/dev/sda1', but this doesn't work. My kernel has no initrd, and is booted directly by a bootloader. It has no modules, so I know that's not the issue.
The current setup that works consists of a ramdisk that the bootloader loads into RAM before booting the kernel. The kernel detects this ramdisk and the current kernel root option ('root=/dev/ram') mounts the ramdisk as the root fs with no problems.
I can see where the kernel detects the flash driveat startup, and I can't think of a reason why I couldn't just mount it as root. I can copy/paste startup logs here if necessary.
Any ideas or help would be very appreciated.

Last edited by arew264; 11-29-2008 at 09:18 PM.
Old 11-30-2008, 11:39 PM   #2
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Registered: Jan 2004
Location: NJ, USA
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The problem with using a USB device as a root filesystem is that the kernel doesn't always detect and initialize it in time to be mounted.

I seem to recall there were some kernel tweaks that could help with the issue, but most people just use an initrd to get a base system up and running (and give the system time to initialize the USB device). From there you could mount the USB device to load additional libraries and binaries, for example by mounting it as /usr/local.
Old 11-30-2008, 11:50 PM   #3
Registered: Jul 2005
Distribution: Arch Linux / Debian Etch (soon) / have tried many others
Posts: 94

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Thanks, I think I'll try mounting it as /usr.

Just for explanation, I'm running a skeleton kernel on an ARM microprocessor. I have 16 MB of flash memory and 32 MB of RAM, and I'm afraid I'll need more than 16 MB for the system when all the programs I need a present.


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