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Re: RAID1 root on nslu2

Hi Stephen

On 5/14/07, Stephen Fry <stephen.fry@tiscali.co.uk> wrote:

I then realised that the configuration for the root device must be in flash
somewhere, so I thought I'd try flash-kernel to update the kernel and
initramfs. (BTW how does it know what to mount as the root file system? I
assumed that doing update-initramfs read the /etc/fstab and stored it

The script /usr/share/initramfs-tools/hooks/nslu2 is run when updating
the initramfs. In that script, there is code to read /etc/fstab and
write the root device listed in the fstab to a file called
conf/param.conf in the initramfs.

For instance, I have an NSLU2 with the root partition in an LVM
logical volume. The fstab line for my root device is

/dev/mapper/vg0-root /               ext3    defaults,errors=remount-ro 0 1

and the contents of param.conf that is generated by update-initramfs is

$ cat conf/param.conf

(To see the above file, I unpacked my initramfs [1].)

This script (param.conf), when executed by the call_scripts function
(in scripts/functions in the initramfs), sets the ROOT parameter,
which is used by the mountroot function (in scripts/local in the

For your system (root partition on a RAID device), I think (but I have
not tried it) that putting /dev/md5 in your fstab, running
update-initramfs and flash-kernel would work once you set the
rootdelay parameter (see below).

I haven't checked yet but would the flash-kernel overwrite the change
to the root delay in the apex environment?

No, flash-kernel doesn't touch /dev/mtdblock2, which is where APEX is
stored. To add the rootdelay parameter to the kernel command line,
follow the instructions at


I have found that to use a root partition in an LVM logical volume on
a USB disk, a rootdelay parameter of 10 seconds works well (it can
probably be less, but this has never failed for me). It should work
for a root partition on a RAID1 device on USB disks, because the delay
is only required to give the USB disks a chance to register with the
kernel (see scripts/init-premount/udev in your initramfs). mountroot,
mentioned above is called after the scripts in

Let me know how it goes, and if I should make any changes to these
instructions. As you pointed out, the bits about modifying fstab, and
running update-initramfs and flash-kernel, should be added to the wiki
page. It is from emails such as this one that most of the wiki pages I
write are developed. I may finally get round to finishing the NSLU2
root on LVM/RAID page with the help this email thread :-)


[1] http://kernel-handbook.alioth.debian.org/ch-initramfs.html

Gordon Farquharson

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