declarative partition and format with Guix (was Re: Guix System automated installation)

[Giovanni Biscuolo <g@xelera.eu>]

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Hello Ian,

Ian Eure <ian@retrospec.tv> writes:

> Giovanni Biscuolo <g@xelera.eu> writes:

[...]

>> Please consider that a preseed file is very limited compared to 
>> a
>> full-fledged operating-system declaration since the latter 
>> contains the
>> declaration for *all* OS configuration, not just the installed 
>> packages.
>
> I appreciate where you’re coming from, I also like the one-file 
> system configuration, but this is inaccurate.

Yes you are right, I completely misrepresented the functionality of the
Debian preseed utility, sorry! (...and I used that in a remote past)

[...]

> installed packages.  Right now, Debian’s system allows you to do 
> things which Guix does not.

[...]

> means you can use a preseed file to tell the installer to 
> partition disks, set up LUKS-encrypted volumes (and specify one or 
> more passwords for them), format those with filesystems

Yes, this is what is missing from the Guix installer system

> With Debian, I can create a custom installer image with a preseed
> file, boot it, and without touching a single other thing, it’ll
> install and configure the target machine, and reboot into it.  That
> boot-and-it-just-works experience is what I want from Guix.

I understand that it's just a workaround but you can achieve this
boot-and-it-just-works (if there isn't bugs in the script/preseed)
experience with a simple bash script to automate "manual installation"

I wrote it in bash because I'm not able to write it in Guile and/or
extend the "guix system" command to be able to manage the missing bits,
but that is a solution (more a workaround now)

[...]

> There’s no facility for specifying disk partitioning or *creating* 
> filesystems in the system config -- it can only be pointed at ones 
> which have been created already.

Yes: those facilities are missing, we (still?) cannot do that
declaratively... let's do that imperatively, automatically :-)

[...]

>> I would really Love So Much™ to avoid writing imperative bash 
>> scripts
>> and just write Scheme code to be able to do a "full automatic" 
>> Guix
>> System install, using a workflow like this one:
>>
>> 1. guix system prepare --include preseed.scm disk-layout.scm 
>> /mnt
>>
>> where disk-layout.scm is a declarative gexp used to partition, 
>> format
>> and mount all needed filesystems
>>
>> the resulting config.scm would be an operating-system 
>> declaration with
>> included the contents of preseed.scm (packages and services
>> declarations)
>>
>> 2. guix system init config.scm /mnt (already working now)
>>
>> ...unfortunately I'm (still?!?) not able to contribute such code 
>> :-(
>>
>
> I don’t think there’s any need for a preseed.scm file, and I’m not 
> sure what would be in that,

preseed.scm is "just" the part of "operating-system" declaration without
the (bootloader [...]), (file-systems [...]) and (swap-devices [...])
declaration, that is automatically generated by "guix system prepare"
based on disk-layout.scm

> but I think this is close to the right track.  Either operating-system
> should be extended to support things like disk partitioning, and
> effect those changes at reconfigure time (with suitable safeguards to
> avoid wrecking existing installs),

I would prefer not, such "reconfigurations" should be done "out of band"
and not "in band", IMHO

> or the operating-system config could get 
> embedded in another struct which contains that, similar to the 
> (image ...) config for `guix system image'.  I think there are 
> some interesting possibilities here: you could change your 
> partition layout and have Guix resize them

Root (/) partition resizing must be done with root unmounted, no?

Also, since the resize (shrink?) of filesystem is a very sensitive
operation, I'd exclude that from "normal" operations done via "guix
system reconfigure"... it's more "guix system prepare..." with one or
more disk partitions (i.e. /home) resized/shrinked or kept as is,
_without_ file system (re)formatting.

One interesting thing that could be done at "guix system prepare" time
is to restore one or more filesystem content from a (possibly remote)
backup, useful in a disaster recovery scenario.

> / create new ones for you.

[...]

Meanwhile: WDYT to work togheter on a simple _configurable_ bash script
to help users automate the very first installation of a Guix System and
try to upstream it?

Thanks! Gio'

-- 
Giovanni Biscuolo

Xelera IT Infrastructures

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