On the raspberry pi 3 for checking temperature of CPU core there are two ways.
First method if you are running official raspbian, second method for any other Linux distro like Kali
Method I:
$ vcgencmd measure_temp
output:
temp=45.1'C
Method II:
$ cat /sys/class/thermal/thermal_zone0/temp
output:
45084
Both are reading 45 degree Celsius
=> turn HDMI off to reduce current requirement
to turn off:
/opt/vc/bin/tvservice -o
to turn on
/opt/vc/bin/tvservice -p
