dual boot(grub?) problem

Question

I’ve got a question about the boot order. See I’m trying to set up a simple dualboot with ubuntu 16.04(server) on one ssd and 18.04(server) on the other.

In the grub the order is

16.04
16.04advanced mode
18.04
18.04advanced mode

When I log in to the 16.04 and edit grub,the GRUB_DEFAULT=0 means it will launch 16.04 on the next boot,but if I change it to GRUB_DEFAULT=2 it launches 18.04

Once in 18.04,if I change the line to GRUB_DEFAULT=0, it boots only 18.04(unless I manually pick 16.04),and no matter what order number I specify it still launches 18.04

Got any ideas what could help ?

Answer 1

Set GRUB_DEFAULT=0 in both systems (don't forget sudo update-grub).

Then install additional instances of grub to your ESP, from 16.04 run

sudo grub-install --bootloader-id=Server16.04

and from 18.04 run

sudo grub-install --bootloader-id=Server18.04

Check your boot-menu-entries with efibootmgr -v. Example:

$ efibootmgr -v
BootCurrent: 0001
Timeout: 0 seconds
BootOrder: 0000,0001,0002,0005,0003
Boot0000* ubuntu    HD(1,GPT,249ac0f6-d3e4-4b91-91d5-6e8d63c093c3,0x800,0x9a000)/File(\EFI\ubuntu\grubx64.efi)
Boot0001* US1804    HD(1,GPT,249ac0f6-d3e4-4b91-91d5-6e8d63c093c3,0x800,0x9a000)/File(\EFI\US1804\grubx64.efi)
Boot0002* US1604    HD(1,GPT,249ac0f6-d3e4-4b91-91d5-6e8d63c093c3,0x800,0x9a000)/File(\EFI\US1604\grubx64.efi)
Boot0003* UEFI OS   HD(1,GPT,249ac0f6-d3e4-4b91-91d5-6e8d63c093c3,0x800,0x9a000)/File(\EFI\BOOT\BOOTX64.EFI)
Boot0005* US1810    HD(1,GPT,249ac0f6-d3e4-4b91-91d5-6e8d63c093c3,0x800,0x9a000)/File(\EFI\US1810\shimx64.efi)

Now make use of EFI's next-boot feature with

efibootmgr -n XXXX

where XXXX is the hex-number of the desired boot entry. Example:

efibootmgr -n 5

will boot to 18.10 on next boot, so the only thing left is to reboot.