BusyBox – Missing Modules and UUID Doesn’t Exist

Cause

In version 23, the mkinitcpio resolve_device() function is called only once. When at execution time the drive labels are not yet read, blkid can't lookup the kernel drive (/dev/...) name for the requested label.

Solution

By adding the "without-udev" hook, as listed below, the resolve_device function is left untouched. Though standard available mkinitcpio functionality to override the mount_handler add a run_hook is used to poll until blkid returns a value, or (a timeout of) 10 seconds has passed. Thus the "udev" hook can be removed from mkinitcpio config.

Notes

• This solution was created with the help of falconindy.
• There was an error message in the early boot phase involving fsck. To remove that message the without-udev hook has been rewritten to use a run_hook instead of a mount_handler. The newer code is even shorter.

$ cat /usr/lib/initcpio/hooks/without-udev
#!/bin/ash
# Minimal initramfs files are created without udev.
# This hooks provides a polling disk mount replacement for udev.
# Udev hook can be removed, resulting in smaller initramfs files.

run_hook () {
    local dev timeout sleepval device=$root
    # if udev is running then exit
    [ "$udevd_running" -eq 1 ] && return
    # try for (timeout * sleepval =) 10 seconds to handle slow (USB) devices
    timeout=1000
    sleepval=0.01

    case $device in
        # label to resolve, when resolved the kernel block device also exists
        UUID=*|LABEL=*|PARTUUID=*|PARTLABEL=*)
            while [ $timeout -gt 0 ]; do
                timeout=$((timeout - 1))
                dev=$(blkid -lt "$device" -o device)
                [ -n "$dev" ] && timeout=0 || sleep $sleepval
            done
            ;;
        # kernel named block device, poll for existence
        /dev/*)
            while [ $timeout -gt 0 ]; do
                timeout=$((timeout -1))
                if [ -b "$device" ]; then
                    dev=$device
                    timeout=0
                else
                    sleep $sleepval
                fi
            done
            ;;
    esac
}

# vim:set syntax=sh:

$ cat /usr/lib/initcpio/install/without-udev
#!/bin/bash

build() {
    add_runscript
}

help() {
    cat <<HELPEOF
This hook provides support for booting without the "udev" hook,
including support for UUID, LABEL, PARTUUID, PARTLABEL.
HELPEOF
}

# vim: set ft=sh ts=4 sw=4 et:

On giving this another look, it seems you have a mismatch between PARTUUID=... and UUID=... and that's what's causing this problem.

You mentioned bootloader is configured with:

options root=PARTUUID=2251a5a4-6c18-425c-9264-df971d297b09 rw

But when you manage to boot it, you actually find this UUID under /dev/disk/by-uuid:

kodi@BB-8:~$ ls -al /dev/disk/by-uuid/
lrwxrwxrwx 1 root root  15 Jul 26 11:10 2251a5a4-6c18-425c-9264-df971d297b09 -> ../../mmcblk0p2

Furthermore, that's even listed in /proc/cmdline of the successful boot (I'm assuming it's the one with SuperGrub USB):

/proc/cmdline output

BOOT_IMAGE=/boot/vmlinuz-4.19.0-5-amd64 root=UUID=2251a5a4-6c18-425c-9264-df971d297b09 ro

The two UUIDs are different. PARTUUID= is the UUID that will be found in the GPT partition table (that's why it's called "PART", because it's a property of the partition, recorded in the partition table), while UUID= is a UUID recorded in the filesystem (ext4, or xfs, or whichever filesystem you formatted the partition with) and Linux is able to read those while scanning the disks.

So, it looks like you need to fix your boot options to use UUID= instead of PARTUUID=, since the UUID you have is a filesystem UUID and not a partition UUID.

Edit file /boot/efi/loader/entries/debian.conf and replace the last line with:

options root=UUID=2251a5a4-6c18-425c-9264-df971d297b09 rw

That should fix your issue!

Make sure your /etc/fstab in the system also matches the correct tag.

You can also use the blkid command to inspect the UUIDs present in your partitions and filesystems. This might help you confirm that you have the correct kind of UUID.

For instance, using blkid -o export should display something like:

$ sudo blkid -o export
DEVNAME=/dev/mmcblk0p1
SEC_TYPE=msdos
LABEL=boot
UUID=9A8B-7C6D
TYPE=vfat
PARTUUID=abcd1234-01

DEVNAME=/dev/mmcblk0p2
UUID=2251a5a4-6c18-425c-9264-df971d297b09
TYPE=ext4
PARTUUID=abcd1234-01

...

That should help you see all UUIDs with a tag that is recognized by Linux.