Need some boot help pls, Debian, Wheezy and WIN7, Debian only sees GRUB changes

Still very much a Linux nube so I need to ask about GRUB and how it works with dual and triple boot systems.

I have Debian 10, (the first Linuxcnc install after WIN7) then I added Wheezy to try it for latency with 2.8.2, and I am testing 8 or 10 older PCs and have changed the GRUB while booted into Wheezy but when I make the changes to GRUB, run update-grub, when I boot back into Wheezy the changes aren't picked up but if I boot into Deb10 and make the changes there, the changes are also picked up when I boot to Wheezy.

What I need to know so I don't have to keep booting into DEB to make changes then boot into Wheezy is, what can I do to just edit a GRUB that will only makes changes for Wheezy?

Thanks for the help..learning still continuing.....

Cheers

I would have recommended using multiple hard disk drives.... one for each operating system.

with my current setup I actually clone it to a second hard drive as my quick backup and restore.

with regards to grub....
have you tried installing grub customizer
itsfoss.com/grub-customizer-ubuntu/

there are many other examples too


plus how to set up grub with multiple os'
linuxconfig.org/booting-a-ms-windows-os-using-grub

It will depend where grub looks for the grub config file.

So while each installation of Linux has it's own /boot/grub/grub.cfg file only one of these will be read by the grub boot loader.

One solution is to edit the actual /boot/grub/grub.cfg file that the boot loader actually reads. In your example it would be the DEB10 installation. This would require you to mount the DEB10 partition where the grub.cfg file is and edit that file directly.

When you edit the grub.cfg directly there is no need to run update-grub. Be warned that you must be very careful.

Another way, tho booting takes longer, is install a grub bootloader to your Wheezy partition, not the MBR, and have grub on the MBR chainload the second grub bootloader. At this stage setting things up can get rather convoluted.

The simplest way is to boot into DEB10 make your changes there and run update-grub.

Or for temporary changes you can edit the kernel command line within the grub environment prior to booting your selected OS.

Another option: Having Grub load a config for another partition. Haven't tried this one myself, and not too sure if Whhezy & Buster both use the same version of grub.

wiki.gentoo.org/wiki/GRUB2/Chainloading

More info
unix.stackexchange.com/questions/343632/...ading-grub-from-grub

More info, just to confuse things a little more
wiki.archlinux.org/title/GRUB

Chainloading:
quick-adviser.com/what-is-chainloader-grub/

Hopefully there's enough info the drive you to drink

Any confusion just ask and I'll try to explain the bits you don't understand or seem a bit weird.

thank you THANK YOU, tHAnk you.

After about 2 hours of playing with it I figured out what happens to the GRUB, and it's exactly what you described, DEB10 is the system grub and is what the boot loader reads. I just did what you suggested and modded that grub and ran various tests. Good to know I don't need to run grub-update after I make the direct changes, saves one step.

Found one PC today which appears to be the one to use, it's a friends old gigabyte board that I replaced a few years ago as it was crashing occasionally, it's been sitting outside for 2 years (under cover) but turns out it was the PS, it kicks butt 18mS max jitter and .9uS sDev. I still have a few more to try...we have a recycle center locally that I have managed to trade beer cans for computers, the beer cans to them are worth $$, the computers get crushed so I have been doing my best to get some trades for this coming week. 

Thanks again for the help. much appreciated.

cheers

Fantastic, glad to be of help.

Another couple of weeks and you'll be a guru. To me it appears you have the right mindset and you seem to have the right amount of curiosity, which is The Secret.

A reliable 18ms is very good, no need to go chasing every millisecond. Once you reach a certain latency, a usable one, it's reliability that counts.

Kilohertz wrote:

we have a recycle center locally that I have managed to trade beer cans for computers, the beer cans to them are worth $$, the computers get crushed so I have been doing my best to get some trades for this coming week. 

Great to see you got it sorted. If you need help emptying the beer cans, I'm sure we could help