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Old 09-18-2005, 09:51 AM   #1
Registered: Jun 2004
Location: Germany
Distribution: Debian (testing)
Posts: 276

Rep: Reputation: 33
Kernel Trouble: VFS: Cannot open root device

I'm having trouble compiling a new kernel.

Here is my system:
Debian Testing (fresh install--downloaded the Testing netinstall CD on friday), Kernel 2.6.12

I'm trying to complie a new kernel so that I can have the cx8800 driver for my TV Card, but I keep getting this:

VFS: Cannot open root device "hda1" or unknow-block(0,0)
Please append a correct "root=" boot option
Kernel panic --- not syncing: VFS: Unable to mount root fs on unknown-block (0,0)
I've compiled my own Debian kernels before, so I don't know why this isn't working.

From what I gather from my own looking into this problem this message might be related to the root file system being a module, but that is not the case with me---I complied it into the kernel.

Here is the relevant section from grub/menu.lst
title Debian GNU/Linux, kernel
root (hd0,0)
kernel /boot/vmlinuz- root=/dev/hda1 ro

title Debian GNU/Linux, kernel (recovery mode)
root (hd0,0)
kernel /boot/vmlinuz- root=/dev/hda1 ro single

title Debian GNU/Linux, kernel 2.6.12-1-386
root (hd0,0)
kernel /boot/vmlinuz-2.6.12-1-386 root=/dev/hda1 ro
initrd /boot/initrd.img-2.6.12-1-386

title Debian GNU/Linux, kernel 2.6.12-1-386 (recovery mode)
root (hd0,0)
kernel /boot/vmlinuz-2.6.12-1-386 root=/dev/hda1 ro single
initrd /boot/initrd.img-2.6.12-1-386
The stock kernel 2.6.12-1-386 works just fine, and I even copied over its configuration file to start my own config and the only things I did differently was make the Conextant cx8800 module a module in the Video for Linux section and tell it that the processor was a P4.

The compile goes fine and I get a deb file that installs okay, but always the same error. I've combiled 5 kernels over the past two days trying varius things, but all for nought.

So, any ideas?


Is there a good way to get a module built and inserted into a stock kernel without a complete recompile?
Old 09-18-2005, 10:38 AM   #2
Registered: Sep 2004
Distribution: Debian Etch
Posts: 179

Rep: Reputation: 30
To me, it looks like an essential part of the kernel (root filesystem or maybe something else) is not present in the compiled kernel, but as a module. The original kernel probably has put this into the initrd (initial ramdisk), which is loaded at boot time to provide those necessary modules at boot. Your new kernel doesn't have an initrd, so it probably can't access those modules at boot and that's why it hangs.

You can't put modules into a compiled kernel as far as I know, you'll not a completely recompile the kernel. What you can do is create your own initrd based on your new kernel. I have done this in the past, but I don't recall how I did it. You need to look on Google how to create an initrd in Debian and especially how you specify which modules need to be present in the initrd.

Another thing you can do is to recompile your kernel and compile those necessary modules into the kernel (so not as modules). This way you don't need an initrd.

Good luck.
Old 09-19-2005, 02:41 PM   #3
LQ Newbie
Registered: Sep 2005
Posts: 2

Rep: Reputation: 0
Thanks Maccloud compiled everything into the kernel and yes it works better no more kernel panic with VFS. Problem is now that i have problems with devfs.
i saw that devfs is no longer supported for the kernel and udev should do the job.

What do i need to do for udev in grub? i tried devfs=nomount at the kernel line

title Debian GNU/Linux, kernel
root (hd1,0)
kernel /boot/vmlinuz- root=/dev/sdb1 ro devfs=nomount
initrd /boot/initrd.img-

Keep getting error 432!

Any suggestions?



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