Cannot use systemd-boot with a squashfs-based root filesystem

[IsaacJT]

Problem description

Combining using systemd-boot as the EFI bootloader and a read-only squashfs filesystem as root does not work, as bootctl fails to write the /etc/kernel/entry-token file in the root filesystem during installation (as it's already been squashfs-ified and is thus read-only).

[ DEBUG   ]: 14:11:15 | EXEC: [chroot /var/tmp/kiwi_mount_manager.t1x8uuuf bootctl install --esp-path=/boot/efi --no-variables --entry-token os-id]
[ DEBUG   ]: 14:11:16 | EXEC: Failed with stderr: Created "/boot/efi/EFI/systemd".
Created "/boot/efi/loader".
Created "/boot/efi/loader/entries".
Created "/boot/efi/EFI/Linux".
Copied "/usr/lib/systemd/boot/efi/systemd-bootx64.efi" to "/boot/efi/EFI/systemd/systemd-bootx64.efi".
Copied "/usr/lib/systemd/boot/efi/systemd-bootx64.efi" to "/boot/efi/EFI/BOOT/BOOTX64.EFI".
Failed to write entry token 'ubuntu' to /etc/kernel/entry-token
, stdout: (no output on stdout)

Expected behaviour

Kiwi can systemd-boot to be used as the bootloader in EFI mode.

Steps to reproduce the behaviour

Use the following appliance configuration snippet:

<type image="oem" overlayroot="true" overlayroot_write_partition="false" firmware="efi" ...>
            <bootloader name="systemd_boot" />
... 
</type>

OS and Software information

• KIWI version: 9.24.61
• Operating system host version: Ubuntu 23.04
• Operating system target version: Ubuntu 23.04
• Open Build Service version (N/A if not using OBS): N/A
• Koji version (N/A if not using Koji): N/A

[IsaacJT]

bootctl install tries to write to the file here: https://github.com/systemd/systemd/blob/main/src/boot/bootctl-install.c#L507

[IsaacJT]

Looking at the code, this will also fail in the next stage due to trying to write to /etc/kernel/cmdline: https://github.com/OSInside/kiwi/blob/master/kiwi/bootloader/config/systemd_boot.py#L143