How to Find Your Raspberry Pi OS (Raspbian) Version
When you've got so many Raspberry Pi's laying around, it's easy to forget which version of Raspberry Pi OS (formerly Raspbian) you're running. In this guide, I'll show you how to find which version of Raspberry Pi OS is running on your Raspberry Pi.
Note: If you're not using Raspberry Pi OS, visit this guide to check your Linux version (and distribution).