how to open grub.cfg in the ESP?

[jlittle]

... by "multiple installs," what do you mean?

Several distros installed at the same time.

Say you want to give Disco Dingo a try. Alongside your normal Kubuntu, you set up a partition for it and install to that. Then, maybe you decide it's not ready yet, and delete it. Next reboot, you get

grub >

and a blinkiing cursor; the grub rescue prompt. When disco installed, it took control of grub, which then can't find itself, because you deleted it.

Or, maybe you install Linux Mint on another drive. You like it, and use it for some tasks, but keep Kubuntu for your main install. On Kubuntu, you customize grub for something, maybe a nice theme, or a kernel parameter to address a hardware issue. One day you log into Mint, it updates itself, and your nice theme is gone, or your hardware stops working.

I encountered problems like this early in my use of Kubuntu, and it never occurred to me to avoid the problems by disabling the mount of the EFI partition except in one install. There's still the problem that at the installation time the new install will take over the boot, but I know to go back to my main install and rerun grub-install there. I mentioned this point thinking someone like my old self would find out about this approach; there are others, like not using grub, or using UEFI features to control the boot.

[Qqmike]

Hi jlittle. Thanks for your explanation. I may have another solution for the "multiple installation" issue.

First, yes, "the last GRUB installed" controls the booting. Frustrating. But you can always boot back into your controlling GRUB OS and issue grub-install and update-grub, which I know you know.

Side note: I keep refind installed just for fun, for a backup, and in case I have to help someone else with it. But, if it gets an update, then it takes over BootOrder #1 (in efibootmgr listing). So, I either leave it that way or change back to my regular OS GRUB by one of two ways: (1) Use efibootmgr to change the ordering; or (2) Boot into the OS and do grub-install and update-grub.

OK, so back to the subject:

In my how-to, I describe 5 ways to dual boot. It is this how-to:

UEFI Simplified, a quicker version
https://www.kubuntuforums.net/showth...l=1#post379977

and the 5-ways described there:

5 methods for dual booting:
#1, #2, #3, do nothing special:
(1) Use rEFInd. (2) Use GRUB2-EFI. (3) Use the UEFI firmware.

Or, try #4 or #5:

(4) Ubuntu-based OSs: set up separate subdirectories of EFI: /boot/efi/EFI/<some_ubuntu_distribution>
Set up the dual-boot: Both LinuxX and LinuxY are Ubuntu derivatives, using the same ESP.
Disable Secure Boot in firmware. Install LinuxX, boot into it, then:
Code:
sudo grub-install --bootloader-id=<some_name_for_LinuxX> --no-uefi-secure-boot Repeat with LinuxY. Optional: adjust BootOrder and generate new boot menus.

(5) Separate ESPs:
GParted: set up the ESPs and the OS partitions you need, give each ESP a label you will recognize. Install each OS, in sequence, with this procedure: Turn off all ESPs (turn off their boot flags) except for the ESP you wish to be used by the OS you are about to install now. Install the OS using the Manual installation method. Repeat for each OS. Then turn on all ESPs (re-set their boot flags in GParted).

See the Methods #4 and #5, especially #5 using separate ESP (one for each OS). Re #5, if you set that up, and then boot into any of the OSs, issue this command:
df /boot/efi
and it will show you the sdxn of the ESP that is mounted at /boot/efi for THAT specific OS (that you have booted into).