(stupid) how to specify the root-device via kernel parameters

(stupid) how to specify the root-device via kernel parameters

[Christoph Anton Mitterer]

Hi,...

Ok this might sound really stupid, but I've seen several ways of doing
this and want to get this cleaned up.

Nevertheless....

kernel-parameters.txt has the following options where you can specify
the root-fs and related flags:
root=           [KNL] Root filesystem
nfsroot=        [NFS] nfs root filesystem for disk-less boxes.

Plus further options like: ro, rootdelay=, rootflags=, rootfstype=,
rootwait, etc.


My question:
These are intended (especially root/nfsroot) to really name the device,
on which the filesystem directly lays, right?
E.g. if the ext4-root-fs is on /dev/sda1,... => root=/dev/sda1

I've seen several initramfs scripts (which I'd like to fix),... where
people abuse this or misuse this in setups where a root-fs is used on
multi-stacked block layers (e.g. something like disk->lvm->dm-crypt->fs)


Cheers,
Chris.

Re: (stupid) how to specify the root-device via kernel parameters

[tytso]

On Sat, Jun 26, 2010 at 01:59:09PM +0200, Christoph Anton Mitterer wrote:
> 
> My question:
> These are intended (especially root/nfsroot) to really name the device,
> on which the filesystem directly lays, right?
> E.g. if the ext4-root-fs is on /dev/sda1,... => root=/dev/sda1
> 
> I've seen several initramfs scripts (which I'd like to fix),... where
> people abuse this or misuse this in setups where a root-fs is used on
> multi-stacked block layers (e.g. something like disk->lvm->dm-crypt->fs)

Abuse this how?  What do you think is "wrong"?

							- Ted

Re: (stupid) how to specify the root-device via kernel parameters

[Christoph Anton Mitterer]

On Sat, 2010-06-26 at 09:46 -0400, tytso@mit.edu wrote:
> Abuse this how?  What do you think is "wrong"?
Uhm... not totally sure as I only had a first short glance on it (so I
hope not to step on Bastian's toes ;) )... but the lvm2 initramfs-script
from Debian's lvm2 package somehow to set up the VGs/LVs... which is
fine, expect you have fully encrypted fs (with boot on USB stick),...
and you have a dm-crypt device on top of LVM.
Not sure why he simply doesn't do a vgchange -an or so,.. but will ask
him.

Then my root is /dev/mapper/root or so,... and the script has it's
problem.


Cheers,
Chris.