dual boot install

[fwm]

My current partition table is as follows:

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Device     Boot     Start       End  Sectors  Size Id Type
/dev/sda1  *         2048  72962047 72960000 34.8G 83 Linux
/dev/sda3        72962048 145862655 72900608 34.8G 83 Linux
/dev/sda4       145862656 220833791 74971136 35.7G 83 Linux
 free           220833792 413618175 192784384 91,93 G
/dev/sda2       413618176 488396799 74778624 35.7G  5 Extended
/dev/sda5       486397952 488396799  1998848  976M 82 Linux swap / Solaris

Bullseye 11.9 is in /dev/sda1. I plan to put the latest debian - Bookworm in
the next available free partition ie /dev/sda3 .
Upon startup I want the option of booting either one. I also Bookworm to
operate independently of bullseye ie if bullseye "breaks".

How do I achieve this result.

[manyroads]

Have you looked at any of the hundreds of tutorials available? Here are some...

https://duckduckgo.com/?q=debian+dual+b ... 1-1&ia=web

[fwm]

I may not have read the "hundreds" that you refer to -
but over the years I have read enough to know that -
the subject is a "minefield" - a turnoff - propelling one
to stick to stick with Windows.

I am a retired college professor. Your attitude reminds me of
" old-school " teaching - If you don't have the answer- go find
it and don't bother me.

[sunrat]

Use Advanced Install from the main Debian install image. I don't think the live installer can do dual boot properly (may be wrong but I'm not gonna check right now). Take your time to read and understand the options in Advanced install, it's more advanced ( ) than the simple installers.
In the partitioning step select sda3 for / . Select sda5 for swap but do not format it as that will mess up your Bullseye swap, or leave it out and add swap later from your new Bookworm after install.
Install Bookworm and reboot. After booting your new Bookworm, edit /etc/default/grub and change

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#GRUB_DISABLE_OS_PROBER=true

to

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GRUB_DISABLE_OS_PROBER=false

then run

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update-grub

and it should add Bullseye to you Bookworm GRUB boot loader.

[fwm]

Thanks - I will try the steps you outlined.

[pbear]

I don't think the live installer can do dual boot properly (may be wrong but I'm not gonna check right now).

Worked fine for me, on two computers. Standard installer worked fine on a third.

[sunrat]

I don't think the live installer can do dual boot properly (may be wrong but I'm not gonna check right now).

Worked fine for me, on two computers. Standard installer worked fine on a third.

Were you able to select to not format the swap partition? That was the main concern I had.

[pbear]

Were you able to select to not format the swap partition?

Frankly, I don't remember. Not an issue I get hung up over, as it's easily repaired. Either (i) edit fstab of the other systems or (ii) revert the swap UUID with mkswap -U and edit fstab of the latest installation. As it happens, I recall having to do that for the computer on which I used the Standard Installer, as it was all eight desktops in a test box and I did them one right after the other. Didn't know about the Advanced option, obviously. Have added to my notes.

Edit: I'm spending part of the day learning KVM (my day off), so decided might as well test this as a way to play with the levers. Turns out, no, Calamares does not automatically reformat a swap partition, although it's an option; indeed, default is to Keep (rather than Format). Another thing to know (I'd forgotten). The live sessions have by default re-enabled os-prober. So, as shipped to keep; edit /etc/default/grub to disable.

By the way, @fwm, if you decide to use the Calamares installer, notice there's an option whether to install Grub to the device (which will put the new system in charge) or the root partition (which will leave the current system in charge). Both options work. If you choose the latter, you need to boot the old system and run update-grub (after enabling os-prober, if not already); the new system won't appear on the Grub menu until you do.

[Augie77]

By the way, @fwm, if you decide to use the Calamares installer, notice there's an option whether to install Grub to the device (which will put the new system in charge) or the root partition (which will leave the current system in charge). Both options work. If you choose the latter, you need to boot the old system and run update-grub (after enabling os-prober, if not already); the new system won't appear on the Grub menu until you do.

My first dual boot was last night, with Mint being the first OS in use, I used the Manual option. I had pre-partitioned the existing NVME with space for Debian. I did not select a Swap partition as I never found it being used in Mint. Maybe I erred in the judgement. However, I did put Grub (seemed the thing to do) in the root. First boot was to Debian grub with the aqua(?) screen, but next two boots to Mint erred with a 'no found memory' or similar. It puzzled me for a moment when I recalled the os-prober said it was updating the UEFI. I booted to UEFI, selected the Mint install and booted to Mint. I then ran the

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update-grub

and could then boot to the standard grub with selections for Mint and Debian.

I am actually surprised my first dual boot went that well, considering I have only used Mint for a little over a year. I installed the KDE Debian on one partition, with Mint XFCE on the other. I strongly suspect that Debian will become my main OS.