Fixing your Debian NAS from within initramfs-tools

<p>

The following article was contributed by John Cass.  Note that John's
instructions will also work on other NAS machines running Debian, such
as QNAP devices.

</p>

<p>

I had a problem upgrading my Debian kernel to 2.6.32 on the D-Link
DNS-323.  The upgrade looked like it worked but on reboot I had a hung
machine.  I tried taking the disk out, putting it in my main machine and
remaking the links in <tt>/boot</tt> to the previous kernel and
initrd.img but it turns out that on the DNS-323 both kernel and
initrd are actually stored in flash memory (the <tt>/boot</tt> disk
files are where they are built and a useful archive but are not used
during the boot process).

</p>

<p>

So I was stuck, and had to make a serial cable in order to find out what
was going on.  The instructions <a href =
"http://buffalo.nas-central.org/index.php/Use_a_Nokia_Serial_Cable_on_an_ARM9_Linkstation">here</a>
and <a href="http://dns323.kood.org/hardware%3Aserial">here</a> were very
useful and the CA-42 clone cost me 4 GBP on eBay and arrived within a
couple of days.  A delicate bit of soldering (and installing ckermit on
my main machine) and I had a serial connection - I could finally see
what was was happening.

</p>

<p>

The upshot was, during the boot process the DNS-323 failed to mount my
root partition.  This was because the partition was formatted ext3 and
the initrd.img had not included the ext3 module.  It probably did this
because I had deliberately forced mounting it as ext2 in the
<tt>/etc/fstab</tt> (in an attempt to limit the write access to the
disk, I want it to stay in standby for a long time but that's another
post). (Remark by Martin: this is a <a href =
"http://bugs.debian.org/519800">known issue</a> with
<tt>initramfs-tools</tt>.)

</p>

<p>

Anyway, having seen this, Martin was able to guide me to getting it fixed:

</p>

<ul>

<li>First of all, I issued <code>modprobe ext2</code> to get the ext2
module loaded (luckily this was included in initrd.img).</li>

<li>Then you can mount the root partition on <tt>/root</tt>: <code>mount
-t ext2 /dev/sda2 /root</code> - it will complain a bit but will work
fine.</li>

<li>Then run <code>/scripts/init-bottom/udev</code> - this moves /dev to
within the new root directory.</li>

<li><code>chroot /root /bin/sh</code> - shift the root around so we are
working from the proper root disk</li>

<li><code>mount -t proc none /proc</code> - mount the proc tree</li>

<li><code>mount -t sys none /sys</code> - and the sys tree</li>

<li><code>nano /etc/fstab</code> - edit this to change ext2 back to ext3
for the root partition</li>

<li><code>mount -t ext2 /dev/sda1 /boot</code> - mount the boot
partition if it's a different device (mine is)</li>

<li>Edit <code>/etc/initramfs-tools/modules</code> and add both
<code>ext2</code> and <code>ext3</code> - this will force their
inclusion in the updated initrd.img</li>

<li>run <code>update-initramfs -u</code> to regenerate the kernel and
initrd.img - this will rebuild the files in <tt>/boot</tt> and it will
use <code>flash-kernel</code> to put them into the flash memory</li>

<li><code>umount /proc /sys /dev /boot</code> - unmount filesystems</li>

<li><code>exit</code> - leave the chroot</li>

<li><code>umount /root</code> - unmount the root partition</li>

<li><code>reboot</code></li>

</ul>

<p>

And it should all be working!

</p>

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