Hello Enrico,

Thank you for your reply, and confirmation of my understanding. Due to 
limit storage space on our device, we need to use a small update/rescue 
OS and our much larger main OS. I expect our rescue/update OS may just 
be a script (to start with) to mount the USB drive and run rauc on a 
pre-set file name, maybe flashing some of our LEDS as it does its work!

Kevin Golding


On 17/05/2018 16:22, Enrico Joerns wrote:
> Hi Kevin,
>
> On 05/17/2018 04:29 PM, Kevin Golding wrote:
>> Hello,
>>
>> Am just getting my head around RAUC, and wondered if I'm right in 
>> thinking that a rescue system is not included with RAUC? i.e. I would 
>> need to find or create a small bootable rescue system that would run 
>> the RAUC update command say via say from a file on a USB stick?
>
> conceptually RAUC is a generic update framework that can run on your 
> Linux device and handle safe and atomic updates of partitions etc.
> It does neither provide any ready-to-use distribution nor depend on 
> any specific.
>
> Thus building a system is always a task that should be solved outside 
> of an update tool. With OE/Yocto, PTXdist and buildroot good build 
> system exists for this that allow you to generate well defined 
> customized systems in versioned and reproducible manner.
>
> RAUC also does not depend on any specific source for its update 
> artifacts. Neither on the production system nor on any rescue system. 
> You can fetch your update from USB / network / storage media or 
> whatever fits your concept or platform.
>
> Nevertheless, conceptually a rescue system is surely supported. A slot 
> configuration for your rescue system (and the default ones, too) would 
> look like
>
>   [slot.rootfs.0]
>   device=/dev/mmcblk0p1
>   ...
>
>   [slot.rootfs.1]
>   device=/dev/mmcblk0p1
>   ...
>
>   [slot.rescue.0]
>   device=/dev/sda1
>   ...
>
>
> This would allow detecting RAUC that it is not running from one of the 
> normal rootfs partitions but from the rescue partition instead and 
> that it can safely upate the others.
>
>> If I am right, are there any examples of a rescue system available?
>
> No. A rescue system can be as small as only a minimal 
> kernel+initramfs+dtb with RAUC binary + dependencies which will result 
> in a few kB. Most of the build systems above provide a minimal rootfs 
> configuration that you can simply extend with RAUC.
>
> https://rauc.readthedocs.io/en/latest/integration.html
>
>
> Did that roughly point you in the right direction?
>
>
> Best regards, Enrico
>
>