Boot from USB on dualboot system


I have a Sony vaio SVT1312V9E that has a UEFI boot (secure boot disabled).
After a lot of effort, I managed to have a dual boot GRUB-EFI with Opensuse 13.1 and Windows 8.1.

I was thinking in upgrading to Windows 10 and I have heard that it is usually a painless process and it doesn’t screw up the booting.
However, I would like to create some kind of USB boot disk that would allow me to boot Opensuse (in /sda6) in case something goes wrong.
It is much easier to repair a system if you don’t have to go into emergency mode, booting some live CD and then trying to repair everything from the command line.

Is it possible to copy the boot partition and have a bootable USB like I be booting normally with the hard drive?

Thank you very much!

You should be able to boot via the BIOS efi setup. Press whichever key eg F2, F12 to get the Sony boot menu, then it should show the openSUSE 13.1 boot entry? If it does then you can boot this way.

The upgrade will create an additional partition, eg on this system;

sda      8:0    0 119.2G  0 disk 
├─sda1   8:1    0   260M  0 part /boot/efi
├─sda2   8:2    0   128M  0 part 
├─sda3   8:3    0    40G  0 part /
├─sda4   8:4    0  78.4G  0 part <= WinX
└─sda5   8:5    0   449M  0 part <=== created after upgrade from Win7 to WinX

Download and create a 13.1 live USB device with imagewriter;

Then you can boot from this, login, then open a terminal session, switch to root user (just su - and press enter, there is no root password).

Then use efibootmgr to identify your openSUSE efi entry, then run;

For example;

efibootmgr -v

BootCurrent: 0000
Timeout: 5 seconds
BootOrder: 0002,0000,0001,0080
Boot0000* openSUSE    HD(1,800,64000,b9444bd2-9878-49a3-81fd-8dc36da19559)File(\EFI\opensuse\grubx64.efi)
Boot0001* openSUSE Secureboot    HD(1,800,64000,b9444bd2-9878-49a3-81fd-8dc36da19559)File(\EFI\opensuse\shim.efi)

efibootmgr -n 1

BootNext: 0001 <==
BootCurrent: 0000
Timeout: 5 seconds
BootOrder: 0002,0000,0001,0080
Boot0000* openSUSE
Boot0001* openSUSE Secureboot

shutdown -r now

It will then reboot into openSUSE secure boot (Boot0001).