When I meet some problem, if i can’t do any thing, I will reinstall system. But can’t we make the install program into many parts? Like install GRUB, I can’t do it successfully(Don’t ask why), but install program can do this. And some other things, like rebuild /etc, /var…
I think we can, right? Linux isn’t windows.
You are not the first person to encounter problems trying to get Grub to work. 
As for piecemeal installs, that’s essentially what dnf does, but it is by-package, not by-filesystem-path. Many programs/packages have components spread across several filesystem paths, so what is under a particular path (e.g. /etc) will vary depending on what you have installed.
sudo dnf reinstall grub2-common
what is the recipe you are following? What problems are you facing specifically?
For grub, also see The GRUB2 Bootloader – Installation and Configuration :: Fedora Docs and Working with the GRUB 2 Boot Loader :: Fedora Docs
grub2-install --target=x86_64 --boot-directory=./grub2 /dev/sda
It return /usr/lib/grub/x86_64/modinfo.sh.
Anyway, why I can’t install isn’t important. If the install program can do it why I need to do it by myself?
What do you want to do? We need a bit more information…
Can fix problems thar reinstall system can fix,but don’t need do all things about reinstall.
If you know the specific issue, I’m thinking it’d be easier to fix the issue vs a larger-scale partial reinstall/restore with everything else.
I’m thinking it’s possible, but:
- Most distros wouldn’t expect or test for it (people either clean-install or upgrade)
- This might be easier to pull-off on Atomic/Immutable OSs
- With the time it’d take me to research and come up with a solution for this with files and bootloader stuff, I can probably just reinstall a dozen times
(I can clean-install to production-ready in about 2 hours any OS)