Using GRUB's chainloader +1, results in the following error
condition upon booting:
error: invalid signature
This is likely caused by GRUB not installing to the partition you
specified. (ie. grub-install /dev/sda4)
You can verify if GRUB is installed to the boot sector of a
partition by using "dd if=/dev/sda bs=512 count=1 | xxd" or "dd
bs=512 count=1 if=/dev/sda4 | od -Ax -tx1z -v" or "hexedit
/dev/sda4"; and viewing blocks 0x1FE-0x1FF (000001FE-000001FF) and
ensuring they contain "55 AA". Or that the bytes before
000001F8 contains ASCII date relevant to the GRUB boot sector or
whatever boot loader you are using.
A common reason why GRUB2 hasn't installed when using "grub-install"
(even though GRUB has stated everything was installed fine), is that
the grub-pc package was not installed and only grub-efi packages
were installed. So if you're using Debian, a likely solution
is uninstalling the grub-efi related packages keeping the
grub-common packages, and then either reinstalling grub-common
packages are additionally selecting the grub-pc package to
install. Afterwards upon using grub-install, you'll likely now
see some warnings when installing to any partition instead of the
main disk MBR, and you should now also see the beginning sectors of
the partition containing grub data!
Further reading, "Details
of GRUB on the PC"; http://www.pixelbeat.org/docs/disk/; Pádraig Brady; Copyright July 28, 2005.
Enjoy the author's note concerning, "Note also the official
grub docs on these disk areas which appeared about
7 years after I wrote the notes above." I also agree GRUB2
isn't the most user intuitive piece of software! For example,
the above error I wrote about is initially very non-descriptive,
leading to a number of possible solutions; above which is the most
undocumented solution and yet likely the most trivial to solve.