So what is the right way to make a backup in Linux (Ubuntu)?

Question

Backup

Computer with UEFI. The OS was Ubuntu 13.04 x64. Two backup options were made: through squashfs-tools, through deja-dup.
There is a need for restoration. I made a recovery from the squashfs image, after booting from the live sd. I reboot, the system refuses to boot. I understand that it is possible that I copied the files from the image, only to the root partition. I forgot about the small /boot partition. I try again by copying the necessary files from under the live sd. The result is the same.
Okay, let's try another option. I clean up the system and restore from a full deja-dup backup that contains the root partition. As a result, I get some kind of curved system. Both backups did NOT include the "home" folder. It was copied separately. I'm very interested in why the backup through "squashfs" did not work correctly.

Answer 1

Why do you need a system backup?
After all, you can make a backup of configs and data, as well as a list of packages.
If necessary, install the system from scratch, install packages according to the list, return the configs to their places.

Answer 2

And what does it mean for you to "correctly" make a backup? What are the criteria?