I just have to share my method to test distros headless with my OdroidN2. The N2 boots eMMC before SD card, so what I did was to flash the SD card with an armbian distro and get it up and running. 

 

the SD card always shows up on mmcblk0 and the eMMC on mmcblk1. So it boots from SD when it can't find a bootloader on the eMMC. I can flash any image easily with

dd if=image of=/dev/mmcblk1

and just do a reboot, and it will boot the eMMC.

 

Whenever I want to test another image, i can just do

dd if=/dev/zero of=/dev/mmcblk1 bs=1M count=1 

to make the eMMC unbootable, causing it to start on the SD image on the next reboot.

 

A very nice way to test stuff out remotely. I only know it works on the N2, but the concept should be appliable to other SBCs (maybe USB/SD boot..?). I'm sure it's nothing new but the "aha" moment for me was the blanking of the bootloader (doing an unbounded dd if=/dev/zero of=/dev/mmcblk1 caused my device to hang not being able to reboot).

Not that this won't work, but is a dangerous way to go about it. If the new image doesn't boot for some reason, you can't recover remotely.

 

On 6/17/2021 at 5:56 PM, Nitrax said:

Whenever I want to test another image, i can just do

dd if=/dev/zero of=/dev/mmcblk1 bs=1M count=1 

 

 

 

The sectors used by u-boot / ATF / etc vary by board. This will also destroy the MBR partition table if it exists. Unless the board uses GPT, you'll likely nuke all your data too.

Yes this is only for testing distros and nuking the data is assumed. I should have been more clear about this!