Re: wip blog post: running Guix System on ARM

["pelzflorian (Florian Pelz)" <pelzflorian@pelzflorian.de>]

On Thu, Nov 14, 2019 at 10:29:22AM +0100, Pierre Neidhardt wrote:
> Neat, thanks for this article!
> 

Yes, thank you!  I have not tried yet though.

Maybe add the top add instructions what to do if installation fails
(i.e. flash the SD with another operating system and start anew).


> > Make sure there is an empty /etc, or the new system won't boot
> > properly.
> 
> Isn't this a bug in Guix?
> 
> 

Is installing on the same drive an “official” installation method?  I
mean, it probably works and people can ask for help after using it,
but remaining files from the old system could be problematic.  If this
is dangerous (is it?) then please add a warning.

Also, I wonder:

On Wed, Nov 13, 2019 at 10:21:54PM +0100, Julien Lepiller wrote:
> Then, initialize the system with:
> 
> ```bash
> mount /dev/sda1 /mnt
> mkdir /mnt/etc
> $EDITOR /mnt/etc/config.scm # create the configuration file
> guix system init /mnt/etc/config.scm /mnt
> ```

So the mmcblk you install on is different from the running system’s
mmcblk, otherwise how could you keep your old system’s SD card?

Then the mmcblk device number will change on the running Guix System
and the config.scm will have to be adapted to use the mmcblk before
reconfiguring from the installed Guix System.

Otherwise if you install on the same mmcblk as the running system,
then maybe this could fail if the u-boot partition is too small?  That
would leave both the existing operating system and the new Guix System
unusable.  Maybe there should be more of a warning.

> ### The bootloader
> 
> Because of the way the Guix System is designed, you cannot use an already existing bootloader
> to boot your system: it wouldn't know where to look for the kernel, because it doesn't know
> its store path.  It wouldn't be able to let you boot older generations either.  Most boards
> use the u-boot bootloader, so we will focus on that bootloader here.


More generally, since no old Guix generation can be selected in pure
u-boot when booting (I think) this warrants more of a warning that one
important feature of Guix is missing.

For later: What would a rescue of a broken Guix System look like?  I
do not know if all this works better with grub-efi on supported ARM
systems; I have never tried.

For later, maybe in the manual: Maybe it would be interesting how to
create a reusable SD install image for Guix.  I also remember there
were discussions about making ci.guix.gnu.org build a two-part
bootable installation image in the past, one part with a bootloader
for a specific board and another part general for all boards.

Regards,
Florian