Hi Gábor,

Gábor Boskovits <boskovits@gmail.com> writes:

[...]

>> Christopher suggested I might be able to at least mount the filesystem
>> with the degraded option in the guix rescue environment, which might be
>> something like:
>>
>> --8<---------------cut here---------------start------------->8---
>>          (mkdir "/mnt/broken-root")
>>          (mount "/dev/sda3" "/mnt/broken-root" "btrfs" 0 "degraded")
>> --8<---------------cut here---------------end--------------->8---
>>
>> but we do not know how to proceed from there.
>
> I don't know what would work from here, but here are a few ideas:
> 1. somehow hack the degraded root option into the bootloader config, like
> here:
> https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1229456

Oh great! I was not able to find what it seems a solution to boot: add
"degraded" to the "rootflags=" kernel parameters (ah my ignorance!)

I also find (just now :-S) this message very helpful:
https://www.mail-archive.com/linux-btrfs@vger.kernel.org/msg31265.html

> 2. try to switch_root, using /bin/sh as init, and try to fix the bootloader
> config from there.

This is not strictly needed, all I need to boot is entering the grub
editing mode, boot degraded and solve the problem with "btrfs
replace..." and "btrfs balance..."

I was thinking to permanently add "rootflags=[...],degraded" as kernel
parameter but reading the message I mentioned above:

--8<---------------cut here---------------start------------->8---
Altho if it is indeed true that btrfs will now refuse to mount writable 
if it's degraded like that, that's not such a huge issue either, as the 
read-only mount can serve as the same warning.  Still, I certainly prefer 
the refusal to mount entirely without the degraded option, if indeed the 
filesystem is lacking a component device.  There's nothing quite like 
forcing me to actually type in "rootflags=degraded" to rub my face in the 
reality and gravity of the situation I'm in! =:^)
--8<---------------cut here---------------end--------------->8---

I changed my mind: booting in degraded mode should be done "manually"
just to solve the issue :-)

> 3. see what the original script is doing, either by having a look at how it
> is composed:
> see for example: gnu/system.scm:
> operating-system-default-essential-services,
> gnu/services.scm: %boot-service and most prominently:
> gnu/services/shepherd.scm: shepherd-boot-gexp
>
> Wdyt?

I'm certailny going to study how Guix instruments the booting of a
machine, but I need time... and I'm late :-S

Thank you very much for the pointers, indeed!

[...]

Ciao, Gio'.

-- 
Giovanni Biscuolo

Xelera IT Infrastructures