Thermal or temperature information in Linux is provided by the ACPI (Advanced Configuration and Power Interface) daemon. You can view your thermal information by using any of the following methods;

acpi is a program available for Linux specifically to view ACPI related information for Linux.

To view thermal information, run the following command at the terminal;

acpi -t

and you'll get output as the following

Thermal 0: ok, 0.0 degrees C
Thermal 1: ok, 26.8 degrees C

The program outputs the temperature in degree Celsius unit. To make it return the temperature in Fahrenheit or Kelvin unit, add -f or -k to the command as the following example;

$ acpi -tf
Thermal 0: ok, 32.0 degrees F
Thermal 1: ok, 80.2 degrees F
$ acpi -tk
Thermal 0: ok, 273.1 kelvin
Thermal 1: ok, 299.9 kelvin

If the program is not installed in your system, run the following command at the terminal on a Debian based distribution such as Ubuntu to install it.

sudo apt-get install acpi

Another way to view temperature information is by using the /proc filesystem.

To do that, run the following command at the terminal;

cat /proc/acpi/thermal_zone/TZ00/temperature

The following is the sample output of the command;

temperature:             27 C

It displays the temperature of your system in '“Celcius as provided by ACPI.

Depending on your system, you might have more than just one thermal zone. To view the other thermal zones, change TZ00 with TZ01 and so on.