After installing Ubuntu 22.04, you may found that dual- or multi-boot systems in your PC disappeared. That’s because of the change of Grub boot-loader. And, here’s the step by step guide shows you how to fix it.
Grub 2.06 disable os-prober by default
Ubuntu 22.04 uses Grub 2.06 to provide boot menu on startup, which disabled the os-prober feature by default.
Grub boot-loader uses the os-prober to find out other operating systems installed on the same machine. Since v2.06, it disables the feature by default. Because it’s a potential attack vector to execute os-prober and create boot entries automatically!
Which means, not only Ubuntu 22.04 but also the next Ubuntu 22.10 and higher, as well as other Linux default to Grub 2.06+ will not find other OSes installed on same PC out-of-the-box, until Grub changes the rule.
The solution is quite easy, as user may re-enable this feature either by manually editing the config file or using the Grub Customizer tool.
Method 1: Re-enable os-prober via Grub Customizer
GRUB Customizer is removed from Ubuntu 22.04 repository due to its broken logic! Please use method 2 instead.
Method 2: Edit the Grub config file manually
Without installing anything, user may manually edit the config file and re-enable the feature by adding a new line.
1.) Firstly, press Ctrl+Alt+T on keyboard to open terminal. When it opens, run command:
sudo nano /etc/default/grub
The command will open ‘/etc/default/grub‘ config file via the nano command line text editor.
2.) Next, scroll down and add the new line below:
GRUB_DISALBE_OS_PROBER=”false”
If 'GRUB_DISALBE_OS_PROBER' line already exist, just change its value to 'false'
And, press Ctrl+X, type y and hit Enter to save change.
3.) Finally, apply change by running command:
sudo update-grub
For Fedora with UEFI, the command is grub2-mkconfig -o /boot/efi/EFI/fedora/grub.cfg 
That’s all. Enjoy!
