[GRLUG] Warning: root device /dev/root does not exist - From chroot .deb pkg install

[Tim Schmidt]

I got a very similar error recently, while attaching a usb hard drive
to an OpenWRT wireless router.  Turned out i needed to install the
kernel module for the ext4 filesystem (kmod-fs-ext4 on OpenWRT).  It
was odd indeed to bee able to stat /dev/sdb2 but still get "device
doesn't exist" when attempting to mount it.

Maybe you're running into something similar?