First step is to install lm-sensors.
sudo apt-get install lm-sensors
Then, starts the detection of your hardware sensors:
sudo sensors-detect
Verify that it works:
sensors
It should display something like:
coretemp-isa-0000
Adapter: ISA adapter
Core 0: +46.0C (high = +76.0C, crit = +100.0C)
coretemp-isa-0001
Adapter: ISA adapter
Core 1: +44.0C (high = +76.0C, crit = +100.0C)
GUI:
sudo apt-get install psensor