Install lm-sensors

sudo apt-get install lm-sensors 

After installation type the following in terminal

sudo sensors-detect

You may also need to run

sudo service kmod start

It will ask you few questions. Answer Yes for all of them. Finally to get your CPU temperature type sensors in your terminal.

sensors

Output:

$ sensors
coretemp-isa-0000
Adapter: ISA adapter
Core 0:      +41.0°C  (high = +78.0°C, crit = +100.0°C)  

coretemp-isa-0001
Adapter: ISA adapter
Core 1:      +41.0°C  (high = +78.0°C, crit = +100.0°C)  

w83627dhg-isa-0290
Adapter: ISA adapter
Vcore:       +1.10 V  (min =  +0.00 V, max =  +1.74 V)   
in1:         +1.60 V  (min =  +1.68 V, max =  +1.44 V)   ALARM
AVCC:        +3.30 V  (min =  +2.98 V, max =  +3.63 V)   
VCC:         +3.28 V  (min =  +2.98 V, max =  +3.63 V)   
in4:         +1.85 V  (min =  +1.66 V, max =  +1.11 V)   ALARM
in5:         +1.26 V  (min =  +1.72 V, max =  +0.43 V)   ALARM
in6:         +0.09 V  (min =  +1.75 V, max =  +0.62 V)   ALARM
3VSB:        +3.30 V  (min =  +2.98 V, max =  +3.63 V)   
Vbat:        +3.18 V  (min =  +2.70 V, max =  +3.30 V)   
fan1:          0 RPM  (min = 10546 RPM, div = 128)  ALARM
fan2:        892 RPM  (min = 2136 RPM, div = 8)  ALARM
fan3:          0 RPM  (min = 10546 RPM, div = 128)  ALARM
fan4:          0 RPM  (min = 10546 RPM, div = 128)  ALARM
fan5:          0 RPM  (min = 10546 RPM, div = 128)  ALARM
temp1:       +36.0°C  (high = +63.0°C, hyst = +55.0°C)  sensor = diode
temp2:       +39.5°C  (high = +80.0°C, hyst = +75.0°C)  sensor = diode
temp3:      +119.0°C  (high = +80.0°C, hyst = +75.0°C)  ALARM  sensor = thermistor
cpu0_vid:   +2.050 V

To see HDD temperature Install hddtemp

sudo apt-get install hddtemp

Output:

$ sudo hddtemp /dev/sda        
/dev/sda: ST3160813AS: 34°C

Quick command-line solution; shows temperature in millidegrees Celsius (m°C)

cat /sys/class/thermal/thermal_zone*/temp

Applet

If you are looking for a easier-to-access version, add a Hardware Sensors Monitor to Gnome-Panel:

1. sudo apt-get install sensors-applet - this will install the sensors-applet package

2. Right-click the panel, select Add to panel..., then select this:

3. You're done. You can configure which sensors are displayed by right-clicking the applet and selecting Preferences->Sensors.

   

A good indicator for monitoring temperature, fan speeds and voltage is psensor. It shows output of all sensors, draws graphs. Also selected outputs can be placed in indicator panel.

It can be installed from Ubuntu repositories by typing:

sudo apt-get install psensor

Newer versions of psensor can be installed from ppa:

sudo add-apt-repository ppa:jfi/ppa
sudo apt-get update
sudo apt-get install psensor

It can also draw graphs when you tick the boxes in the graph column:

Here is some information with more pictures.

Another useful link

In some cases not all sensors are displayed. Then you can run

sudo sensors-detect

and answer "yes" to all questions. But is not quite safe in some cases, but I never had any real problems with that. A safer way is to take default answers.

Some additional sensors may appear.

Temperature without third-party apps

At the time of writing, all the answers involve use of third-party utilities. If you want to find out the temperature without installing anything, use:

$ cat /sys/class/thermal/thermal_zone*/temp
20000
53000
50000
53000
56000
68000
49000
50000

To see what zones the temperatures are referring to use:

$ paste <(cat /sys/class/thermal/thermal_zone*/type) <(cat /sys/class/thermal/thermal_zone*/temp) | column -s $'\t' -t | sed 's/\(.\)..$/.\1°C/'
INT3400 Thermal  20.0°C
SEN1             45.0°C
SEN2             51.0°C
SEN3             57.0°C
SEN4             59.0°C
pch_skylake      77.5°C
B0D4             50.0°C
x86_pkg_temp     51.0°C

The temperatures are stored in Celsius with 3 implied decimal places. sed is used to "prettify" output.

The last temperature is x86_pkg_temp reported at 54.0°C. For the Skylake i7 6700HQ CPU, I used this temperature for Conky display below.

Temperature with Conky

If you don't mind third-party utilities I like to use Conky--a light weight system monitor.

Conky commands

Within conky the system variable I used to monitor an Ivy Bridge CPU is:

${hwmon 2 temp 1}°C

To monitor a Skylake CPU I used:

${hwmon 0 temp 1}°C

Conky display

The conky display looks like this:

The temperature starts at 72°C with a single CPU running at 100% in turbo mode of 3200 MHz. Then turbo is switched off and temp drops 10°C to 62°C with a non-turbo speed of 2600 MHz. 10 seconds later turbo is turned back on and temperatures immediately spike back up to 72°C.

Controlling Temperature

After knowing your temperature you probably want to control it better. tlp works wonders for keeping system under control. It works with thermald, Intel Powerclamp, Battery vs AC for USB power, etc. Although highly configurable I've never had to change the configuration settings for a pleasant Out-Of-The-Box experience. Prior to using it I had all kinds of problems with an IvyBridge laptop overheating all the time. I have it on my new Skylake laptop and the fans NEVER run except when doing Ubuntu 16.04 LTS to 18.04 upgrade.

You can get a very detailed write-up with installation instructions here: Stop cpu from overheating

hardinfo is very useful tools to get all hardware information.

Install hard info by sudo apt-get install hardinfo. Then you can get temperature by sensors.

1. install the small package of acpi by this command

   sudo apt-get install acpi
   

2. You will need to press Y for confirmation for the first time. Now to find temperature type this command

   acpi -t
   

After you install lm-sensors:

sudo apt install lm-sensors

run:

sudo sensors-detect

you can run the following command to view hardware temps:

watch -n 1 sensors

Also, the fan is usually controled by BIOS.

Another good tool is i7z for Intel Core processors:

sudo apt install i7z
sudo i7z

and because i7z runs like top, there is no need to use watch.

XSensors

XSensors reads data from the libsensors library regarding hardware health such as temperature, voltage and fan speed and displays the information in a digital read-out.

Open the terminal and type:

sudo apt-get install xsensors lm-sensors

Then detect your computer's hardware sensors by opening the terminal and running the command:

sudo sensors-detect

Then you will get asked a lot of questions about what hardware you want the program to detect. It is generally safe and recommended to accept the default answers to all questions, unless you know what you're doing.

Xsensors vs. Psensor

XSensors and Psensor both monitor the computer's temperature and the fan speeds. The difference between the two applications is in the level of detail of the information that is displayed and how the information is displayed.

XSensors displays a little bit more specific information than Psensor. Psensor is smaller and more unobtrusive than XSensors and it displays itself on the desktop as a little thermometer icon in the notification area in the upper right corner of the desktop. You can right-click the thermometer icon at any time to display the hardware temperatures.

Setting up Psensor to detect your computer's hardware is done the same way as Xsensors, by installing lm-sensors to detect your computer's hardware sensors. Then detect your computer's hardware sensors running the command:

sudo sensors-detect  

and as with Xsensors, accept the default answers to all questions.

In Ubuntu 16.04 and later Psensor detects your computer's hardware sensors automatically without running sudo sensors-detect

On Raspberry Pi, you can retrieve the temperatureusing vcgencmd:

vcgencmd measure_temp

Output:

temp=39.0'C

Just so you guys know, none of this install junk like sensors are needed. Just do an acpi -V and BOOM, you got everything. Example:

Battery 0: Charging, 91%, 00:17:25 until charged
Battery 0: design capacity 3310 mAh, last full capacity 3309 mAh = 99%
Adapter 0: on-line
Thermal 0: ok, 40.0 degrees C
Thermal 0: trip point 0 switches to mode critical at temperature 127.0 degrees C
Thermal 0: trip point 1 switches to mode hot at temperature 127.0 degrees C
Cooling 0: pkg-temp-0 no state information available
Cooling 1: LCD 0 of 100
Cooling 2: Processor 0 of 10
Cooling 3: Processor 0 of 10
Cooling 4: Processor 0 of 10
Cooling 5: Processor 0 of 10

WAY easier than installing all of this and kmod... Just do acpi -V.