A better idea: download the firmware version you're currently running (see here
https://www.mobileread.com/forums/sho...d.php?t=185660 )
extract it and find u-boot and kernel image (called uImage)
then dd those to your sd card with these offsets:
dd if=$UBOOT of=/dev/$DEVICE bs=1K seek=1 skip=1
dd if=$KERNEL of=/dev/$DEVICE bs=512 seek=2048
(taken from the upgrade script in our kobos)