Re: GuixSD on servers [Fwd: [rtracker.1984.is #131647] A question about VServer system specific requirements]

[Chris Marusich <cmmarusich@gmail.com>]

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ludo@gnu.org (Ludovic Courtès) writes:

>> There appear to be (at least) two problem that prevent this naive
>> solution from working, which might point us in the right direction:
>>
>> First, the GRUB menu is trying to find a file system with label
>> "gnu-disk-image" (via "search --label --set gnu-disk-image"), which
>> won't work because there is no file system with that label in the
>> resulting image.
>
> So it seems that the crux of the problem is that ISO9660 lacks file
> system labels, which breaks the whole thing, right?

Yes, probably.  It seems we can set a "volume id", but not a label like
in EXT file systems.  For example, see here:

https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/installer/cd-dvd/iso-image.nix

>> Second, the init process from the initrd (I think that's what it's
>> called?) is trying to look for a file system with label
>> "gnu-disk-image", which it never finds.  It just sits there waiting to
>> find it, and it never shows up, so it freaks out.  Possible solution:
>> modify the behavior of our initrd's init process.  I'm not sure how to
>> customize the init process here, but there must be a way.  We'll
>> probably also need the kernel module that enables reading of iso9660
>> file systems, if it wasn't present already.
>
> So we could try detecting the root partition by a mechanism other than
> partition labels/UUIDs, but I don’t know which mechanism.  Ideas?  How
> do people address this?

Volume ID seems like the right thing to try first.  What do we need to
change to support this, I wonder?  I'm not familiar with the initrd
stuff but would be willing to poke around in there and experiment.  I
just don't really know where to begin.

>> If you don't like grub-mkrescue, you can "roll your own" ISO generation
>> program, like Nix does by customizing the xorriso invocation [1]...  But
>> honestly, it looks pretty complicated [2].  So if we can let
>> grub-mkrescue do that work for us, that would be swell.
>
> Indeed, though of course grub-mkrescue invokes xorriso behind the
> scenes.
>
> Once we’ve figured out the partition designation issue above, I guess we
> could integrate that and have, say,
>
>   guix system iso-image …
>
> to produce an ISO image.  Sounds doable!

Yeah, that'd be cool.  It looks like with the right incantations (see
Nix's scripts), you can create a "hybrid" ISO image that boots correctly
in PC-BIOS, UEFI, from CD/DVD or USB stick.  But any ISO image that will
boot from a CD is a good start.

By the way, do you think it's possible to build an ISO image from a
manifest of files?  I ask because it seems like that's what Nix is
doing; however, the code involved in 'guix system disk-image' seems to
actually boot the target system before the final disk image is built.  I
was playing around by mounting the disk image as a loopback device only
because that provided me with a convenient way to access all the files
that need to be in a bootable system; it seems to me like it would be
great if we could build an ISO image without first building an entire
disk image.  That seems redundant.

-- 
Chris

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