[gentoo-user] Does root=PARTUUID=<> work with DOS partition table?

[Grant Edwards]

I'm trying to install Gentoo with root on a USB SSD.  In order to
allow for varying enumeration order of USB block-storage devices, I've
configured grub to search for its root by using the filesystem label,
and that seems to work.

Since I'm not using an initrd, on the kernel command line I can't use
root=LABEL=<> or root=UUID=<>.  Right?

But, supposedly I can use root=PARTUUID=<>.

That doesn't seem to work.  The kernel always reports

   cannot open root device "PARTUUID=4e66c96c-01"

Where 4e66c96c-01 is the PARTUUID value shown by the blkid command.

I've tried a rootdelay of up to 20 seconds, and that doesn't seem to
help.

All the examples I can find of people using root=PARTUUID=<> show the
longer PARTUUID values you get with a GPT parition table.  Does the
root=PARTUUID=<> mechanism only work with GPT and not with DOS
parition tables?

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