[lfs-support] Kernel panic: VFS: unable to mount root fs

Nathan Bibb nathanbibb at gmail.com
Sun May 15 12:46:02 PDT 2016

On Sun, May 15, 2016 at 3:37 PM, Bruce Dubbs <bruce.dubbs at gmail.com> wrote:

> Paul Rogers wrote:
>> I have finished all steps in LFS 7.9 on my old pentium -mmx machine,
>>> and rather than overwrite the existing grub configuration, I ran "update-
>>> grub" from the host Debian 7.5 system.
>>> The LFS system was found and showed up in my Grub Menu, but when I
>>> boot to that, I got the kernel panic mentioned in the subject line.
>> Not to belabor the point, it's telling you that once the kernel
>> completes startup it can't get to your root file system to start init.
>> Presumably the kernel that booted is from LFS, not the Debian host.  The
>> key configuration at this point is in /etc/fstab.  It, and the
>> "root=/dev/sdaX" in your GRUB configuration, had better agree on where
>> your new system is.
> I did confirm that /etc/fstab and the grub command line agree as far as U
can tell.

> I agree with Paul, but as an interesting aside, I once accidentally booted
> a LFS partition with a debian kernel/initrd and it came up.  There were
> some issues because /lib/modules did not have the debian modules, but I did
> get to a command prompt.
> In my experience, 'make defconfig' for the kernel is generally sufficient
> for an initial boot.  There may be some issues with some peripherals such
> as a network card driver missing, but it is probably enough to get a bash
> prompt.
> Maybe I will recompile the kernel with 'make defconfig' rather than 'make
menuconfig'.  It's possible I messed something up there.

If we are relatively confident that 'make defconfig' should boot, and I get
the same issue, I am thinking that we can narrow down the issue to how
Debian constructs the GRUB entry when using 'update-grub' from the host.
Does that sound reasonable, or is there something I'm missing?

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