lsb_release
Reading the systemPackage: lsb-release
The distribution's name and version, also held in /etc/os-release. The answer to the first question of every fix: "which release are you on?"
What its options do in the lessons
From the same glossary the lessons render under their commands, so the two cannot disagree.
lsb_release -a- Prints the distribution, its version and its codename.