## Description Installs GRUB for EFI/GPT images using FUSE partition mounts (`fuse2fs`), chroot, and `mtools`, eliminating the need for kernel loop devices and host filesystem bind mounts (`/dev`, `/proc`, `/sys`). ### The Problem Previously, installing GRUB required attaching a kernel loop device to the image, mounting all partitions, bind-mounting host `/dev`, `/proc`, and `/sys`, chrooting in, and running distribution `grub-install` and `update-grub`. This required host root privileges and loop device access, preventing builds in unprivileged environments. ### The Approach - **FUSE & mtools**: Root (and optional boot) partitions are mounted via FUSE (`mount_partition`). ESP files are written in place with `mtools` without kernel loop devices. - **Binary Deployment**: Deploys pre-signed Ubuntu shim+GRUB if present (for Secure Boot), or builds a standalone GRUB EFI binary using the image's `grub-mkimage` inside the mounted rootfs. - **Config Generation**: Uses `update-grub` inside the mounted rootfs (via chroot) to discover kernels and generate `grub.cfg` and ESP stub configs, avoiding the need for `grub-mkimage` in the rootfs. The `grub-probe` stub handles device queries from precomputed UUIDs. ### Scope Only the **EFI/GPT** path is converted. Legacy BIOS/MBR continues using the loop-device path until a follow-up change. IMAGECRAFT-176 --- - [x] I've followed the [contribution guidelines](https://github.com/canonical/imagecraft/blob/main/CONTRIBUTING.md). - [x] I've signed the [CLA](http://www.ubuntu.com/legal/contributors/). - [x] I've successfully run `make lint && make test`. - [ ] I've added or updated any relevant documentation. - [ ] In documents I changed, I [added a meta description](https://canonical-starflow.readthedocs-hosted.com/how-to/add-a-page-meta-description/) if one was missing.