BTW am not so technical,
Linux is not MS-Windows...
Ubuntu's grub/grub2 loader may not be showing all yor bootable partitions.
Read this ubuntu explanation
https://help.ubuntu.com/community/Grub2/Setup
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Self discovered this with an Ubuntu default installation did not enable multi-boot(s), with only the installed ubuntu available.
With grub showing only needed provide address to start other bootable partitions.
Entering correct boot address for other bootable partitions, can have them start.
When at grub/grub2 command-line prompt and know your bootable partition addresss [eg sda2]
EXAMPLE: set root=(hd0,sda2)
then ENTER your boot partition address, for self this proceeded to boot.
IF access your linux OS partion, best re-build your grub addresses.
Example: opensuse
mount /dev/sdb8 etc wipes contents of sdb7?? What's up wit dat?
IF access your linux OS and run the into sort partion.
With linux OS running update your grub, it find other OS's.
GPT is the newer standard replacing MBR.
GPT drives tend to include a “protective MBR.”
This type of MBR says that the GPT drive has a single partition that extends across the entire drive.
Trying to manage GPT disks with old tools may only read MBRs, may see single partition as extending across entire drive.
The protective MBR ensures old tools do not mistake GPT drives thus overwrite GPT data with a new MBR.
In other words, the protective MBR protects the GPT data from being overwritten.
When you make a change to a grub file make sure to
run the
[self with opensuse] "sudo grub2-mkconfig -o /boot/grub2/grub.cfg"
So your bootable partitions are recognised and usable.
