Verification:
On a system w/ /boot on an md device:
dannf@mdraid:~$ sudo grub-reboot 0 [sudo] password for dannf:
WARNING: Detected GRUB environment block on diskfilter device 0 will remain the default boot entry until manually cleared with: grub-editenv /boot/grub/grubenv unset next_entry
On a system w/ /boot on a /dev/vda: ubuntu@ubuntu:~$ sudo grub-reboot 2 ubuntu@ubuntu:~$
And it worked as expected.
Verification:
On a system w/ /boot on an md device:
dannf@mdraid:~$ sudo grub-reboot 0
[sudo] password for dannf:
WARNING: Detected GRUB environment block on diskfilter device
0 will remain the default boot entry until manually cleared with:
grub-editenv /boot/grub/grubenv unset next_entry
On a system w/ /boot on a /dev/vda:
ubuntu@ubuntu:~$ sudo grub-reboot 2
ubuntu@ubuntu:~$
And it worked as expected.