Create support for the ubuntu-minimal images

[afbjorklund]

Description

The regular ubuntu images got really big, but there is a "minimal" version...

https://cloud-images.ubuntu.com/minimal/releases/

Hopefully it can be done without having to increase the number of templates.

Note: the minimal images lacks e.g. git and vim

[AkihiroSuda]

Note: the minimal images lacks e.g. git and vim

The minimal ones should have plain: true by default?

[afbjorklund]

The minimal image worked OK with the default setup...

images:
- location: https://cloud-images.ubuntu.com/minimal/releases/resolute/release/ubuntu-26.04-minimal-cloudimg-arm64.img
  arch: aarch64

param:
  internal_netplanOptional: "true"

i.e. with the agent and with nerdctl, so plain is optional

It is not really "minimal", it is more like "half bloated"

[Nachiket-Roy]

I'm looking into this. The current implementation direction is to support the Ubuntu minimal images through a parameter/variant mechanism rather than introducing additional templates, which should allow us to keep the existing template set unchanged while still letting users opt into the smaller image variant.

[Nachiket-Roy]

The Ubuntu 24.10 and 25.04 templates correspond to releases that have already reached end-of-life, and Ubuntu 25.10 will reach EOL in the near future.

As Canonical archives EOL releases outside of the standard image streams, these templates will eventually stop updating and may no longer be downloadable.

Should i open a follow-up PR to clean up the EOL interim Ubuntu templates?

[afbjorklund]

I don't think that "minimal" should have a separate lifecycle to the others.

[Nachiket-Roy]

@afbjorklund @AkihiroSuda yes i am thinking of a better approach, a template-less approach using yq-based filtering instead of separate templates. To avoid managing a separate lifecycle for minimal entirely, we wouldn't introduce minimal-specific templates at all. Instead, by adding a variant tag to each image entry, users can filter the standard template directly:

limactl start --image-variant=minimal template:ubuntu-24.04

Since the minimal and standard entries would live in the same _images file, updated by the same script in the same pass, minimal automatically has the exact same release lifecycle and availability as server — no duplicate files, no separate update tracking, no drift between the two.

[afbjorklund]

I think the preferred approach* was to keep it simple and just do multiple templates. Instead of exposing yq on the user.

* #5156 (comment)

[Nachiket-Roy]

I've already fixed it by using a dedicated string flag, so users are no longer exposed to raw yq expressions.

The current implementation also preserves the existing behavior: if --image-variant is not specified, Lima continues to use the default (top-level/first) image selection as it does today. Users only need to specify --image-variant when they want a non-default variant.This gives us a simple interface for selecting variants while avoiding multiple templates or exposing heavy filtering expressions.