fix broken kernel upgrade

[suchende]

I made a kernel upgrade which was not successful The kernel does not boot up. Unfortunately armbian does not contain a fallback method to load the old kernel. Therefore I need a way to restore the old kernel. 

I copied a working boot folder from another sdcard which does not work.

 

What did I miss?

[martinayotte]

copying /boot folder is not enough to recover an upgrade, especially if you upgraded U-Boot, this one is installed on sectors outside partitions, usually starting at byte #8192 of the sdcard.

Also, there is the /lib/modules/<kernel-number> that needs to be rescued if deleted after an upgrade, but I don't think it is deleted ...

 

 

[suchende]

 

the dump from fdisk:

p
device         Boot  begin      end  sectors  size Kn typ
/dev/mmcblk0p1        8192 30396575 30388384 14,5G 83 Linux

F
  beginn      end  sectors  size
    2048     8191     6144    3M
30398464 30703615   305152  149M

the raw copy with `dd if=/dev/mmcblk0 of=/dev/sdc skip=2048 seek=2048 bs=512 count=6144 conv=notrunc` fails. Did you meant byte #8192 or sector?

 

the kernel modules are still there.

[martinayotte]

As I said, the u-boot is not inside a partition. Depending of the SoC and boards, the first byte is usally at byte#8192, for example, copying an u-boot image from file to sdcard would be :

dd if=u-boot-sunxi-with-spl.bin of=/dev/mmcblk0 bs=1024 seek=8

If you wish to extract an copy u-boot from a device to another, like you seems to wish, than it would be something like that, assuming that this u-boot is smaller than 500K :

dd if=/dev/mmcblk0 of=/dev/sdc bs=1024 seek=8 skip=8 count=500 conv=notrunc

As you can see, your previous copy was copying an entirely different location ...

[suchende]

Thank you very much. I fixed it with a different approach in while. Take all necessary files in /boot and /lib/modules and copy them. Save the mbr and partition table with fdisk to a file, then copy straight with the dd if=/dev/mmcblk0 of=/dev/sdc bs=512 count=8192 and restore afterwards the saved fdisk dump.

I forget to mentioned it here: the SoC is the odroid HC1.