What happens when you reinstall the root and boot partition?

Question

linux

Hello all connoisseurs!
There is a maximally detailed partitioned system on LVM:
/dev/mapper/main-root /
/dev/mapper/main-usr /usr
/dev/mapper/main-tmp /tmp
/dev/mapper/main-usr-local / usr/local
/dev/mapper/main-data /mnt/data
/dev/mapper/main-srv /srv
/dev/mapper/main-opt /opt
/dev/mapper/main-home /home
/dev/mapper/ main-var /var

/boot partition is outside the lvm volume.

Question: when reinstalling on the same OS of the same version and mounting all the same partitions, except for reinstalling root and boot partitions, what is expected? And how to properly reinstall the system while maintaining the current information on the partitions as much as possible?

Answer 1

how to properly reinstall the system while maintaining the current information on the partitions as much as possible?

In two steps: (1) backup all partitions or the entire disk; (2) restore from backup; just wondering what the meaning is.
Reinstallation is done when something needs to be fixed, but it is not really clear what exactly. And with the maximum saving of the current information on the partitions, nothing will be fixed. So I'm waiting for clarification of the problem.

/dev/mapper/main-usr /var
...
/dev/mapper/main-var /var

How is that?

when reinstalling on the same OS of the same version and mounting all the same partitions, except for reinstalling root and boot partitions, what is expected?

/var when reinstalling, even without formatting, many files will be overwritten, but those that are not in the freshly installed system will be preserved;
/usr is the same as /var;
/usr/local is the same;
/tmp is supposed to be cleared at all on every reboot;
/opt and /srv are not present in every linux installation, depending on the distribution (which you did not name), and may remain unchanged;
/mnt there is nothing to overwrite here, you can expect that the folders for the mount points will be saved (although it won't take long to create them);
/home change the username to make sure the old folder is intact (mostly worrying about all sorts of user configs etc. because documents/downloads aren't going anywhere); after installation, everything can be restored to its previous state.