Thanks Coolie, unfortunately I could not get the command line sensor to work, even though all the commands work when run from the shell as the homeassistant user. I did, however, get the file sensor to work!
What platform are you running HA on?
There are no sensors (lm-sensors) in a VM.
In a Raspberry Pi there is a single temp sensor on the CPU if you can get it to read via lm-sensors.
On physical desktop computers, laptops, and servers there are lots of sensors you can read with lm-sensors. I asked about a lm-sensors to mqtt in another thread but no one replied so I assumed it did not exist.
For example, in my desktop Linux box I have the following built in sensors
fam15h_power-pci-00c4
Adapter: PCI adapter
power1: 78.06 W (crit = 94.92 W)
k10temp-pci-00c3
Adapter: PCI adapter
temp1: +23.8°C (high = +70.0°C)
(crit = +83.5°C, hyst = +80.5°C)
atk0110-acpi-0
Adapter: ACPI interface
Vcore Voltage: +1.00 V (min = +0.80 V, max = +1.60 V)
+3.3V Voltage: +3.17 V (min = +2.97 V, max = +3.63 V)
+5V Voltage: +5.04 V (min = +4.50 V, max = +5.50 V)
+12V Voltage: +11.95 V (min = +10.20 V, max = +13.80 V)
CPU Fan Speed: 2033 RPM (min = 600 RPM, max = 7200 RPM)
Chassis Fan Speed: 1295 RPM (min = 600 RPM, max = 7200 RPM)
CPU Temperature: +40.0°C (high = +60.0°C, crit = +95.0°C)
MB Temperature: +34.0°C (high = +45.0°C, crit = +75.0°C)
I’ve been working on a perl script to pull the sensor data and plug it into MQTT with auto-defined topics.
Right now I have it doing the following
Publishing "<MyHostname>.com/PCIadapter/power1" with "74.63"
Publishing "<MyHostname>.com/PCIadapter/temp1" with "32.0"
Publishing "<MyHostname>.com/ACPIinterface/Vcore Voltage" with "1.36"
Publishing "<MyHostname>.com/ACPIinterface/+3.3V Voltage" with "3.17"
Publishing "<MyHostname>.com/ACPIinterface/+5V Voltage" with "5.07"
Publishing "<MyHostname>.com/ACPIinterface/+12V Voltage" with "11.87"
Publishing "<MyHostname>.com/ACPIinterface/CPU Fan Speed" with "1956"
Publishing "<MyHostname>.com/ACPIinterface/Chassis Fan Speed" with "1315"
Publishing "<MyHostname>.com/ACPIinterface/CPU Temperature" with "39.0"
Publishing "<MyHostname>.com/ACPIinterface/MB Temperature" with "34.0"
There is still a lot of work to do on the script but it is basically running. I have a dual xeon processor motherboard here that has 10x that number of sensors on it. It will be interesting to see when I get it up and running. lol
Personally I started it because I want to monitor the wattage draw on the units in the house. 
I’m trying what you do and when I enter /usr/bin/sensors | grep 'Core 0' | cut -c17-20 I get 39.0 in the terminal. However when I use the following in my config:
- platform: command_line
name: Server Temp
command: "/usr/bin/sensors | grep 'Core 0' | cut -c17-20"
unit_of_measurement: "°C"
the sensor does not show anything. When I try the standard example where I pull the temperature like this it works:
- platform: command_line
name: CPU Temperature
command: "cat /sys/class/thermal/thermal_zone0/temp"
# If errors occur, remove degree symbol below
unit_of_measurement: "°C"
value_template: '{{ value | multiply(0.001) | round(1) }}'
Could it be that there is a problem with cut or grep or something?
Did you try that command from an ssh session?
Quickly off the top of my head, I would try the quotation marks.
If you change them to an exact copy of how I have them, does the sensor then work?
It’s also possible that the homeassistant user doesn’t have the permissions to run that command - so you check that by swapping over to the homeassistant user and seeing if the command still works.
You’re right with the permissions. I made a python script now which publishes on mqtt and gets triggered by a cron job.
When I added processor temperature to system monitor in config it came back and shows in Fahrenheit and wondering how to change that to Celsius. Any help would be appreciated.