Run grub2-install inside the install chroot to use target image's modules

[vinceaperri]

Problem

Image Customizer installs the legacy (BIOS) bootloader by running grub2-install on the build host, which copies grub modules from the host's grub2-pc into the target image. When the host's grub differs from the target's grub, the copied modules don't match the grub.cfg the target's own grub2-mkconfig produces, and the image fails to boot. Concretely, the AZL3-based IC container building an AZL4 image produces a disk whose grub.cfg does insmod blscfg while /boot/grub2/i386-pc/ was populated from AZL3 (no BLS modules), so it errors with file '.../blscfg.mod' not found on boot.

Fix

Install the legacy bootloader from the target's own grub2-install, run inside the install chroot, so the bootloader and its modules always come from the target. Behavior when the target does not ship grub2-pc:

Target distro version	Behavior
grub2-pc present (any version)	Run grub2-install in the chroot (modules come from the target).
AZL2 / AZL3 (out of preview), no grub2-pc	Fall back to the host's grub2-install with a warning — preserves the existing behavior for images whose configs predate this requirement.
AZL4+ (preview), no grub2-pc	Fail with a clear error telling the user to add grub2-pc to os.packages.install.

Container: explicitly install systemd-udev

The IC container's host-side disk setup calls udevadm settle (waitForDevicesToSettle). udevadm is provided by the systemd-udev package, which until now arrived only transitively via grub2. systemd-udev is now listed explicitly in imagecustomizer.Dockerfile so udevadm can never silently disappear if the grub2 dependency changes.

Testing

• Functional: TestCustomizeImagePartitionsLegacy exercises the chroot path (config installs grub2-pc); TestCustomizeImagePartitionsLegacy_TargetMissingGrub2Pc exercises the no-grub2-pc path across AZL2/3/4 — asserting success + a valid legacy image for AZL2/3 (host fallback) and a grub2-pc error for AZL4.
• VM tests: test_legacy_bootloader_reset_azl{2,3,4} boot a hard-reset legacy image built with grub2-pc (chroot path); test_legacy_bootloader_reset_fallback_azl{2,3} boot one built without it (host fallback).

Docs

storage.md documents the new bootType: legacy behavior and the grub2-pc requirement.

[Copilot]

Pull request overview

This PR changes legacy (BIOS) bootloader installation to run grub2-install inside the target image’s install chroot so it uses the target image’s GRUB modules instead of the build host’s.

Changes:

• Run grub2-install via shell.NewExecBuilder(...).Chroot(...) (and drop the host-side grub-install fallback).
• Update legacy boot functional test config to install grub2-pc into the target image and adjust the test to use base-image RPM repos.
• Remove GRUB packages from the Image Customizer container and update host prerequisite documentation / CI package lists accordingly.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
toolkit/tools/pkg/imagecustomizerlib/versionsOfToolDependencies.go	Stops logging host-side grub-install version since GRUB install is no longer host-executed.
toolkit/tools/pkg/imagecustomizerlib/testdata/legacyboot-config.yaml	Ensures grub2-pc is installed in the target image for legacy boot tests.
toolkit/tools/pkg/imagecustomizerlib/customizepartitions_test.go	Switches legacy test flow to use base-image RPM repos so the new package install succeeds.
toolkit/tools/imagegen/installutils/installutils.go	Runs grub2-install inside the install chroot to use target-image modules.
toolkit/tools/imagecustomizer/container/imagecustomizer.Dockerfile	Removes GRUB packages and adds systemd-udev to satisfy udev tooling needs.
toolkit/tools/imagecustomizer/container/build-container.sh	Drops arm64-only Dockerfile patching that is no longer needed after GRUB removal.
docs/imagecustomizer/quick-start/quick-start-binary.md	Updates host prerequisite lists to remove GRUB tools/packages.
.github/workflows/tests-functional.yml	Removes GRUB packages from functional-test host prerequisites (since GRUB install is now in-chroot).

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