I have a Raspberry Pi 3 Model B. I installed Ubuntu MATE but decided to go back to Raspbian as Ubuntu MATE was very slow. But during the short lived time I had with Ubuntu MATE, the processor's temperature go up, so now I am worried, how hot is too hot?

The CPU is pretty hot when doing tasks like `apt-get upgrade`, and when I run `/opt/vc/bin/vcgencmd measure_temp`, temperatures are hovering in the mid 40's to low 50's in °C, which is more than 100°F. Is that not normal?