On Sat, Mar 19, 2016 at 04:09:39PM -0400, N. Morris wrote:
> After rebooting multiple times and checking files and filesystems I do not
> know how to solve the current problem I am facing:
> In the fstab file I have the root fs and swap locations at their UUID and
> all the other stuff as it looks on the website.

That is your problem, as I see you have guessed - the kernel only
understands devices.

For grub.cfg try /dev/sdd2 for the kernel and then similar variants
for swap and anything else mounted from /etc/fstab.  But read on -
the drive might appear at a different device, and it might appear
late.

NB for fstab the entry for '/' is effectively a comment.

> I have it as the UUID since its a usb external hdd and I'm booting on
> different computers all the time.
> 
> The partition where lfs is is /dev/sdd2
> 
> At the grub prompt I do :
> set root=(hd2,msdos2)
> ls (hd2,msdos2)
> <info...info..info..UUID <uuid>>
> linux /boot/vmlinuz-4.5.0 root=UUID=<uuid goes here>
> boot
> 
> I did it like that because that is how the grub config on my drive with
> ubuntu on it looks.
> 
> I also tried where root=/dev/sdc1 and somehow successfully booted my
> partition with fedora on it. But that would be linux mostly not from
> scratch.
> 
> The kernel always panics and says : cannot open root device UUID=<uuid> or
> unknown block (0,0) error -6
> 
> Do I have to use the root=/dev/sdXX method in grub and in fstab or do I
> have to enable some obscure option during kernel config or is it because
> I'm using an external HDD or something else?
> 
> Thanks for your help.

Adding an external drive might make it harder - when there is more
than one drive (and you have at least four) different kernels can
report them in different orders : on one of my machines, adding a
second drive with some other OS, as the second drive according to
grub, made linux think it was the first drive, and adding a third
drive to copy everything onto meant the original drive was now sdc.

These situations are why distros use UUID - but for that to work you
need to use an initrd.  An example is covered in BLFS:
http://www.linuxfromscratch.org/blfs/view/svn/postlfs/initramfs.html

For external drives, people have reported having to add a kernel
parameter to cause it to wait for the rootfs to appear - I am not
sure if that is needed or not with an initrd (I've never used
either).

ĸen
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