Migration from GRUB#

While GRUB has very different requirements for filesystem layout, it is possible to migrate from GRUB to ZFSBootMenu.

First, create a portable installation that will let you boot from a USB drive. This should give you all the tools you need to migrate /boot into the root filesystem in such a way that ZFSBootMenu will recognize your boot environment. Af first, ZFSBootMenu will probably fail to recognize any boot environments and try dropping you into a recovery shell. Assuming your root filesystem is rpool/ROOT/debian and your boot filesystem is bpool/BOOT/debian, you should be able to:

Confirm that bpool and rpool are both imported. If not, you can manually import each pool, or you can try running /libexec/zfunc import_pool which will try to import both.
Make sure the pools are writable:
```
set_rw_pool rpool
set_rw_pool bpool
```

Use the mount_zfs helper to mount both the boot and root filesystems:
```
mount_zfs bpool/BOOT/debian
allow_rw=yes mount_zfs rpool/ROOT/debian
```
each call will print the path where the filesystem is mounted, which (in this case) will be, respectively:
```
/zfsbootmenu/environments/bpool/BOOT/debian/mnt
/zfsbootmenu/environments/rpool/ROOT/debian/mnt
```

Copy the contents of the boot filesystem to the boot subdirectory of the root:

cd /zfsbootmenu/environments/bpool/BOOT/debian/mnt
mkdir -p /zfsbootmenu/environments/rpool/ROOT/debian/mnt/boot
cp -a . /zfsbootmenu/environments/rpool/ROOT/debian/mnt/boot

Make sure the boot pool won't be mounted at next boot:
```
zfs set canmount=noauto bpool/BOOT/debian
```
Exit the recovery shell. You should now see your environment in the menu.

After confirming this works, you can now install ZFSBootMenu in your EFI System Partition and add it to the boot order with efibootmgr (or use a bootloader like rEFInd to load it).

Once everything works, you can destroy your bpool and remove GRUB from the ESP if you so choose.