[solved] Can't get Grub to update; System with Existing LM Installations

[RealDogBoy]

But sudo grub-install /dev/sdX is more elegant and now I know that.

Be aware, that simple command only works if you are booted into the system you want to control Grub.

Absolutely--
I only update grub from the partition which I have set at the top of the bios boot order (Una MATE).
btw--my grub is on a spinner used for data storage--there is no os on this drive at all.
I have a front panel sata hot-swap bay--If I insert a drive with additional os I will do the sudo update-grub
so these os will show.
Contending with several os spread among multiple drives is more complicated--especially with the hot-swap bay.
So all my drives have their own grub--and I could choose to boot them at bios--but the spinner contains the dominant
system-wide grub.

Is that a spinner as in Spintronics as opposed to electronics? If so, that's some next level tech.

I don't understand how grub can be somewhere other than in the proper folder in the os file system. How can it be found? You don't need to explain that for my sake; I'm pretty sure I don't need to know.

Thanks so much for all the help.

[user6c57b8]

Can't get Grub to update; System with Existing LM Installations
... Any ideas?

The proper solution is to boot into a LiveOS:
1) mkdir ~/your-primary-linux-mint-partition-mount-point
2) sudo mount -t ext4 /dev/sdc6 ~/your-primary-linux*
3) Here's the hard part (I'm 3% sure this is going to work right)
ln -s /dev ~/your-primary-linux-mint-partition-mount-point/dev
4) If the above works then we're in:
sudo su
chroot your-primary-linux*
update-grub

Bam that should work.

[pbear]

... how grub can be somewhere other than in the proper folder in the os file system.

To simplify, on a BIOS system, Grub starts with a small file in the MBR which points to the main boot files, usually /boot/grub on a specified partition. There's only room for one Grub-pointer-file in the MBR and the system to which it points is the one we refer to as controlling Grub.

By the way, pretty sure 'spinner' = HDD, as distinguished from an SDD.

[asinoro]

Boot from your live usb of the last installed Mint 20.3 and run boot repair, post the info of boot repair at the forum. That other Linux OS do not boot even if you see at the grub menu, means that the fstab UUID has to be checked and corrected, otherwise the other systems will not boot.

[RealDogBoy]

To Jo-con-Ël, user6c57b8, and asinoro: you joined this thread after I found a solution to my problem but I still would like to thank you for your replies. It's likely that somebody else having a similar problem will read this thread and benefit from your input.

The solution I found (I'd really call it a hack) is detailed on the first page of this thread.

One thing I'd like to add is that I used an outdated (LM 17.2 - not supported with security updates) distribution to work through this issue. That was a risky move and I recommend against going online using any os that's not supported. There are known vulnerabilities out in the wild.

[all41]

I love the shepard avatar@RealDogBoy and I know what 'real dogs' means--just sayin we love the breed.
Once we had 18 including pups

I love the breed and have had five GSDs over the last four decades. But search18 at once... wow.

kind of off subject but
Yes two sets of pups at nearly the same time. I would lead them out in the yard and it was like a wave of pups following me.
I regret not having a .mov for this to show--it was a long time ago. But we loved each and every pup
while they were with us