Hello!
I’m having a problem with either GRUB or uboot (not sure which) after reconfiguring my flashed debian-12-base-arm64+arm64.img to my eMMC on the aml-s905x-cc-v2 (Sweet Potato).
I am not a fan of installing the root filesystem to the top level subvolume (subvolid=5) in BTRFS. Unfortunetly, debian-12-base-arm64+arm64.img is setup that way. After my first boot, I created 4 subvolumes.
# cd /
# btrfs sub create @
# btrfs sub create @swap
# btrfs sub create @home
# btrfs sub create @snapshots
I turn off swap and unmount /boot/efi
# swapoff -a && umount /boot/efi
I move the swapfile into the @swap subvolume and disable swapfile creation by systemd
# mv /swapfile @swap/
# systemctl disable mkswap.service
I then copy everything except for proc, sys, run, tmp, dev into the new rootfs subvolume (@)
# cp -a <everything> @/
I manually recreate the excluded directories and add a couple others in @ and adjust permissions
# mkdir -p @/{proc,sys,run,tmp,dev,toplevel,snapshots,swap}
# chmod 555 @/{proc,sys}
Fixup /@/etc/fstab in the new rootfs
PARTUUID=186ce4b8-02 / btrfs noatime,compress=zstd,x-systemd.growfs,subvol=/@ 0 1
PARTUUID=186ce4b8-02 /swap btrfs defaults,compress=zstd,subvol=/@swap 0
PARTUUID=186ce4b8-02 /home btrfs noatime,compress=zstd,subvol=/@home 0 2
PARTUUID=186ce4b8-02 /snapshots btrfs noauto,noatime,compress=zstd,subvol=/@snapshots 0 2
PARTUUID=186ce4b8-02 /toplevel btrfs noauto,noatime,compress=zstd,subvolid=5 0 2
PARTUUID=186ce4b8-01 /boot/efi vfat defaults 0 1
/swap/swapfile none swap defaults 0 0
Set the new rootfs (@) as the new default subvolume and reboot
# btrfs sub set-default @ && reboot
After reboot, I am in the new rootfs (@) and I re-install and update grub for good measure
# cd / && grub-install --efi-directory=/boot/efi && update-grub
The new /boot/grub/grub.cfg looks like this and note the “/@/boot…” to linux and initrd lines, so it appears Grub is working in the correct rootfs.
#
# DO NOT EDIT THIS FILE
#
# It is automatically generated by grub-mkconfig using templates
# from /etc/grub.d and settings from /etc/default/grub
#
### BEGIN /etc/grub.d/00_header ###
if [ -s $prefix/grubenv ]; then
set have_grubenv=true
load_env
fi
if [ "${next_entry}" ] ; then
set default="${next_entry}"
set next_entry=
save_env next_entry
set boot_once=true
else
set default="0"
fi
if [ x"${feature_menuentry_id}" = xy ]; then
menuentry_id_option="--id"
else
menuentry_id_option=""
fi
export menuentry_id_option
if [ "${prev_saved_entry}" ]; then
set saved_entry="${prev_saved_entry}"
save_env saved_entry
set prev_saved_entry=
save_env prev_saved_entry
set boot_once=true
fi
function savedefault {
if [ -z "${boot_once}" ]; then
saved_entry="${chosen}"
save_env saved_entry
fi
}
function load_video {
if [ x$feature_all_video_module = xy ]; then
insmod all_video
else
insmod efi_gop
insmod efi_uga
insmod ieee1275_fb
insmod vbe
insmod vga
insmod video_bochs
insmod video_cirrus
fi
}
if [ x$feature_default_font_path = xy ] ; then
font=unicode
else
insmod part_msdos
insmod btrfs
search --no-floppy --fs-uuid --set=root ae802f12-183e-4db5-b8a1-d70eba710416
font="/@/usr/share/grub/unicode.pf2"
fi
if loadfont $font ; then
set gfxmode=auto
load_video
insmod gfxterm
set locale_dir=$prefix/locale
set lang=en_US
insmod gettext
fi
terminal_output gfxterm
if [ "${recordfail}" = 1 ] ; then
set timeout=2
else
if [ x$feature_timeout_style = xy ] ; then
set timeout_style=menu
set timeout=2
# Fallback normal timeout code in case the timeout_style feature is
# unavailable.
else
set timeout=2
fi
fi
### END /etc/grub.d/00_header ###
### BEGIN /etc/grub.d/05_debian_theme ###
set menu_color_normal=cyan/blue
set menu_color_highlight=white/blue
### END /etc/grub.d/05_debian_theme ###
### BEGIN /etc/grub.d/10_linux ###
function gfxmode {
set gfxpayload="${1}"
}
set linux_gfx_mode=
export linux_gfx_mode
menuentry 'Debian GNU/Linux' --class debian --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-ae802f12-183e-4db5-b8a1-d70eba710416' {
load_video
insmod gzio
if [ x$grub_platform = xxen ]; then insmod xzio; insmod lzopio; fi
insmod part_msdos
insmod btrfs
search --no-floppy --fs-uuid --set=root ae802f12-183e-4db5-b8a1-d70eba710416
echo 'Loading Linux 6.1.74-12781-g74961fb0a5d2 ...'
linux /@/boot/vmlinuz-6.1.74-12781-g74961fb0a5d2 root=UUID=ae802f12-183e-4db5-b8a1-d70eba710416 ro rootflags=subvol=@ noquiet
echo 'Loading initial ramdisk ...'
initrd /@/boot/initrd.img-6.1.74-12781-g74961fb0a5d2
}
submenu 'Advanced options for Debian GNU/Linux' $menuentry_id_option 'gnulinux-advanced-ae802f12-183e-4db5-b8a1-d70eba710416' {
menuentry 'Debian GNU/Linux, with Linux 6.1.74-12781-g74961fb0a5d2' --class debian --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-6.1.74-12781-g74961fb0a5d2-advanced-ae802f12-183e-4db5-b8a1-d70eba710416' {
load_video
insmod gzio
if [ x$grub_platform = xxen ]; then insmod xzio; insmod lzopio; fi
insmod part_msdos
insmod btrfs
search --no-floppy --fs-uuid --set=root ae802f12-183e-4db5-b8a1-d70eba710416
echo 'Loading Linux 6.1.74-12781-g74961fb0a5d2 ...'
linux /@/boot/vmlinuz-6.1.74-12781-g74961fb0a5d2 root=UUID=ae802f12-183e-4db5-b8a1-d70eba710416 ro rootflags=subvol=@ noquiet
echo 'Loading initial ramdisk ...'
initrd /@/boot/initrd.img-6.1.74-12781-g74961fb0a5d2
}
menuentry 'Debian GNU/Linux, with Linux 6.1.74-12781-g74961fb0a5d2 (recovery mode)' --class debian --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-6.1.74-12781-g74961fb0a5d2-recovery-ae802f12-183e-4db5-b8a1-d70eba710416' {
load_video
insmod gzio
if [ x$grub_platform = xxen ]; then insmod xzio; insmod lzopio; fi
insmod part_msdos
insmod btrfs
search --no-floppy --fs-uuid --set=root ae802f12-183e-4db5-b8a1-d70eba710416
echo 'Loading Linux 6.1.74-12781-g74961fb0a5d2 ...'
linux /@/boot/vmlinuz-6.1.74-12781-g74961fb0a5d2 root=UUID=ae802f12-183e-4db5-b8a1-d70eba710416 ro single rootflags=subvol=@
echo 'Loading initial ramdisk ...'
initrd /@/boot/initrd.img-6.1.74-12781-g74961fb0a5d2
}
}
### END /etc/grub.d/10_linux ###
### BEGIN /etc/grub.d/20_linux_xen ###
### END /etc/grub.d/20_linux_xen ###
### BEGIN /etc/grub.d/30_os-prober ###
### END /etc/grub.d/30_os-prober ###
### BEGIN /etc/grub.d/30_uefi-firmware ###
menuentry 'UEFI Firmware Settings' $menuentry_id_option 'uefi-firmware' {
fwsetup
}
### END /etc/grub.d/30_uefi-firmware ###
### BEGIN /etc/grub.d/40_custom ###
# This file provides an easy way to add custom menu entries. Simply type the
# menu entries you want to add after this comment. Be careful not to change
# the 'exec tail' line above.
### END /etc/grub.d/40_custom ###
### BEGIN /etc/grub.d/41_custom ###
if [ -f ${config_directory}/custom.cfg ]; then
source ${config_directory}/custom.cfg
elif [ -z "${config_directory}" -a -f $prefix/custom.cfg ]; then
source $prefix/custom.cfg
fi
### END /etc/grub.d/41_custom ###
I then mount the toplevel subvolume (subvolid=5) and delete everything except my subvolumes
# cd /toplevel
# rm -fr <everything> ./
# ls -lah /toplevel
drwxr-xr-x 1 root root 50 Dec 18 20:27 .
drwxr-xr-x 1 root root 164 Jan 23 2024 ..
drwxr-xr-x 1 root root 164 Jan 23 2024 @
drwxr-xr-x 1 root root 16 Dec 19 07:35 @home
drwxr-xr-x 1 root root 0 Dec 18 20:18 @snapshots
drwxr-xr-x 1 root root 16 Dec 18 20:21 @swap
I unmount the toplevel and for good measure, I re-run update-grub
# umount /toplevel
# update-grub
Then upon reboot, I’m dropped to the grub command line. 
I start over and instead of deleting everything except my subvolumes, I also keep the boot directory in subvolid=5 and reboot. This time, I am able to successfully boot. When I delete boot from subvolid=5, I’m dropped to the Grub command line again. So, what am I missing? How can I get Grub (or is it u-boot?) to look at the correct subvolume for the correct root filesystem with /boot?