Linux Mint installer has no option NOT to install a bootloader by default. But you can change that.
If you decide to install Linux Mint as your second Linux system, you don’t need to install a bootloader because you already have a bootloader from your primary Linux system. But the problem is that by default you cannot install Linux Mint without a bootloader as you can see above. I will show you how to overcome this obstacle.
What is a Bootloader?
A bootloader is a program that starts your operating system. If you have several operating systems on your computer, your bootloader also allows you choose which one to boot. Normally, you should not have several bootloaders.
So, if you already have a Linux system installed, you also have a bootloader. If you decide to install a second Linux system on a separate partition, you can either overwrite the existing bootloader or keep it and install the system without a bootloader. The rule of thumb is to use that bootloader which is the latest.
There are several bootloaders available for Linux. GRUB is the most popular one. I use GRUB on all my system, Linux Mint uses GRUB as a bootloader and you are also most likely have GRUB bootloader on your system. When I talk about a bootloader here, I mean GRUB bootloader.
Linux Mint installation without GRUB
If you boot from the Linux Mint live image, start the installer by double-clicking on it, follow the installation instructions and select the manual partition, you will see that there is no option NOT to install a bootloader. I think this is a precaution of the Linux Mint team, so new users do not end up with installation without a bootloader.
But if you know what you are doing and you want to install Linux Mint without a bootloader, you need to start the installer from the command line. The Linux Mint installer is called ubiquity. Ubiquity is the installer in Ubuntu and all its derivatives. To see all options available in ubiquity, run:
Among these options, the option -b is what you need. It will install the system without a bootloader.
And when you get into the partition setup, there is no bootloader option you have seen before.
I installed Linux Mint without a bootloader this way and everything went as it supposed to. I can also confirm that this approach works for Ubuntu and KDE Neon. So, ubiquity with the option -b should work on Ubuntu and all its derivatives.
Update your main bootloader
After this installation process, you will need to update your bootloader, so it can see the new system. Also, you need to make sure that the partition with a newly installed system is mounted during the update. For example, if you installed the Linux Mint system without a bootloader on sda2, mount it:
sudo mount /dev/sda2 /media
Then update GRUB bootloader.
On Linux Mint, Ubuntu, Debian, run:
On Arch Linux, run:
sudo pacman -S os-prober && sudo grub-mkconfig -o /boot/grub/grub.cfg
I also explain this process for Arch Linux in more details here. If your distribution is not one of the above, search how to update a bootloader of your distribution.
Please, leave a comment below if you use any other distribution and the command to update the bootloader on your system is different from the above commands. I will add your command here.