Bug#721139: Dual boot with custom bootloader-id

[Jörn Heissler]

Dear Maintainer,

I'd love to get a BOOTLOADER_ID config option too.
My use case is to install multiple debian versions in parallel,
including their own grub version.

This can be useful when upgrading a remote system (without remote
console) from say debian12 to debian13 with minimal risk and minimal
downtime:

There could be two distinct partitions for /boot and / Debian12 uses one
set of those partitions, debian13 the other. When the debian13 install
is done, use "efibootmgr --bootnext" to boot into debian13 and reboot.

In case this fails to boot, a watchdog (or human) can powercycle the
system and it will boot into debian12 again. Otherwise if the new system
works, use "efibootmgr --bootorder" to change the order permanently.

My current workaround is to configure apt (DPkg::Path) to include
/usr/local/sbin which contains a simple wrapper script for grub-install
that appends to --bootloader-id=xxxx param.

Thanks
Jörn