Multi boot Grub lists different OS dependant on which one installs Grub

I have a triple boot system going here at the moment, Linux Mint is my main OS on /dev/sda1 followed by OpenSuse on /dev/sda2 and CentOS 8 Stream on /dev/sda4.

If I run
followed by
grub-install /dev/sda

On Mint the process only finds CentOS and itself. On OpenSuse it finds all 3.
Is this an issue with Mint and the BTRFS filesystem that OpenSuse is using?

Do I have to manually configure Grub or am I missing something?

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I sometimes have the same thing happen to me. I just go into the bios and change the boot order to the one that shows all of the drives.exit,it restarts and walla, done.

The system boots off a single drive though.

I think he meant all of the OS’s.

yes.On startup,(in my case),I press F2 or delete,That brings me to the bios.Go to advanced,then go to boot order and choose the drive that showed all of your drives at boot. <select that one and set it for first to boot.exit and save.system will reboot and you can now choose which one to play on.
Hope this helps you.

It is exactly for this sort of problematic situation that I have my own personal policy, which goes like this:

One hard drive, one OS. Never two OS’ on the same hard drive (and I’m not talking about virtual machines here). Each OS gets to own that whole hard drive, including the Master Boot Record, or GPT equivalent to the MBR. Each OS must leave alone, and ignore the other hard drives, especially when writing GRUB configs (“installing”) to the boot loaders. This still allows a situation where one can boot from multiple OS’, but this keeps them separated, and out of each other’s hair.

I choose which OS from which hard drive to boot from, not from a grub menu, but from the (UEFI) boot menu which my BIOS generates. On my particular laptop, pressing F8 at boot time shows this (UEFI) boot menu.

My laptop has MX Linux installed to the internal M.2 drive, and this is the only OS on that M.2 drive. Then I have an SSD in a USB3 enclosure (type C, which is a “self-latching” connector, making it a bit safer), which has Pop_OS installed on it. MX Linux uses GRUB, but Pop_OS does NOT use GRUB. It uses systemd-boot. Since each OS controls its own separate hard drive, there is no conflict between GRUB and systemd-boot. My BIOS boot menu lets me pick from either hard drive to boot from, and GRUB and systemd-boot never need to know about each other, let alone conflict with each other.

Yes my idea costs a little more money, but so what. I feel that my time is worth it. I want to live a more hassle-free life, and I’m willing to spend a little more to have that.

Yes, my laptop has only one HDD. Although, it actually has 2 drive bays with connections, the enclosure is filled in where the second drive would go. Not that I can’t work around this odd Grub behavior, I’m really curious to know WHY this occurs.