Re: [systemd-devel] With UEFI secure boot and dm-verity, how does one find the user data partition?

Lennart Poettering
2025-10-20T20:27:52Z

On Mo, 20.10.25 15:45, Demi Marie Obenour (demiobenour@gmail.com) wrote:

> >> Unfortunately this isn't what is needed. Looks like UEFI variable
> >> storage is the best option.
> >
> > Partition UUID is (supposed to be) unique for every partition, so it
> > most certainly allows one to identify the device to which it belongs.
>
> I mixed up partition UUID and partition *type* UUID.
>
> What is the best way to use it? The most obvious one requires that
> whenever a block device appears, one checks if either:
>
> - This has the correct partition UUID, and a device with the same
> diskseq and the correct partition type UUID has appeared.
> - This has the correct partition type UUID, and a device with the
> same diskseq and the correct partition UUID has appeared.
>
> Is there a simpler option?

The {Loader,Stub}DevicePartUUID efi var is passed in from the
firmware, which has no concept of a diskseq, hence it's purely a uuid.

systemd v258 and newer make the ESP booted from available via
/dev/disk/by-designator/esp and XBOOTLDR as
/dev/disk/by-designator/xbootldr as symlinks.

Lennart

--
Lennart Poettering, Berlin