I have ubuntu server on emmc working well.
Now I Installed ubuntu desktop to SD card and it also boots well but says that /dev/mmcblk0 is not allocated.
Here are devices that I see so far:
root@Khadas:~# ls /dev/root*
/dev/rootfs
root@Khadas:~# mount /dev/rootfs /mnt/
root@Khadas:~# cd /mnt/
root@Khadas:/mnt# ls
bin dev etc lib mnt proc run srv tmp usr zImage
boot dtb.img home media opt root sbin sys uInitrd var
root@Khadas:/mnt#