Raspberry Pi command line - How to tell the CPU temperature

Simply use the following command:

vcgencmd measure_temp

This will report back the current CPU temperature in deg C. 

Anything above 82C or so and the pi will start throttling to keep the temperature down. 

Above 80C you will see a thermometer icon on the screen exactly like the one above.

The output of the command looks like the following. In this case we had a rather cool pi.