How to understand the output of lm-sensors?

Question

$ sensors
Adapter: Virtual device
temp1:        +27.8°C  (crit = +105.0°C)
temp2:        +29.8°C  (crit = +105.0°C)

coretemp-isa-0000
Adapter: ISA adapter
Physical id 0:  +30.0°C  (high = +80.0°C, crit = +100.0°C)
Core 0:         +30.0°C  (high = +80.0°C, crit = +100.0°C)
Core 1:         +29.0°C  (high = +80.0°C, crit = +100.0°C)
Core 2:         +25.0°C  (high = +80.0°C, crit = +100.0°C)
Core 3:         +23.0°C  (high = +80.0°C, crit = +100.0°C)

it8728-isa-0a30
Adapter: ISA adapter
in0:          +0.01 V  (min =  +0.00 V, max =  +3.06 V)
in1:          +2.02 V  (min =  +0.00 V, max =  +3.06 V)
in2:          +2.04 V  (min =  +0.00 V, max =  +3.06 V)
in3:          +2.03 V  (min =  +0.00 V, max =  +3.06 V)
in4:          +0.01 V  (min =  +0.00 V, max =  +3.06 V)
in5:          +1.79 V  (min =  +0.00 V, max =  +3.06 V)
in6:          +1.54 V  (min =  +0.00 V, max =  +3.06 V)
3VSB:         +3.38 V  (min =  +0.00 V, max =  +6.12 V)
Vbat:         +3.00 V  
fan1:        1066 RPM  (min =    0 RPM)
fan2:           0 RPM  (min =    0 RPM)
fan3:           0 RPM  (min =    0 RPM)
fan4:           0 RPM  (min =    0 RPM)
fan5:           0 RPM  (min =    0 RPM)
temp1:        +25.0°C  (low  = +127.0°C, high = +127.0°C)  sensor = thermistor
temp2:       -128.0°C  (low  = +127.0°C, high = +127.0°C)  sensor = disabled
temp3:        +21.0°C  (low  = +127.0°C, high = +127.0°C)  sensor = Intel PECI
intrusion0:  ALARM

How to understand the output of lm-sensors especially in0~in6, 3VSB, and Vbat?

Answer 1

It can be different for different hardware combinations. Might be best to look at your BIOS/EFI for it's sensor info (it should be correct), and try comparing those to the output from sensors.

The "Adapter: Virtual device" I'm not sure, looks similar to cpu or gpu cores.

"coretemp-isa-0000" with it's 4 cores looks like a 4 core cpu.

Last one "it8728-isa-0a30" looks like motherboard sensors. I'm not sure what each one could be exactly, aside from V's are volages, fan speed RPMs, don't know exactly where the temp sensors could be. Here's where comparing these to the BIOS could be useful.

Web search for "it8728-isa-0a30" found this page for a "Gigabyte B75-D3V" might have better descriptions/labels for them. I think placing it a file in /etc/sensors.d/ (and then maybe a reboot, or at least a sudo service kmod stop and sudo service kmod start (restart the sensors module?).
See the sensors and sensors.conf man pages

Here's a paste of the file from the link Gigabyte link above, even though it does not look like a match for your motherboard, it could be useful if you want to write your own labels yourself:

# libsensors configuration file
# -----------------------------
#
#  For the Gigabyte B75-D3V Rev: 1.2
#
#
#

    ######################################
    # VOLTAGES                           #
    # These figures are from estimations #
    # based on values provided in BIOS.  #
    # This means that some of them may   #
    # be mixed up.                       #
    ######################################


##############################################
chip "it8728-isa-0a30"

########
# Fans
label fan1 "CPU-Fan"
set fan1_min 1000

label fan2 "System Fan 1"
set fan2_min 450

label fan3 "System Fan 2"
set fan3_min 450

label fan4 "System Fan 3"
set fan4_min 450

ignore fan5 #"Chassis Fan" # It is not connected, no pinout available.


################
# Temperatures
label temp1 "System Temperature"
set temp1_min 10
set temp1_max 60

ignore temp2 
#label temp2 "Unknown" # Does not seem to give sensible data (Always shows 25)

label temp3 "Chipset Temperature"
set temp3_min 10
set temp3_max 55


############
# Voltages
label in0 "Vtt"
set in0_min 1.020
set in0_max 1.080

label in1 "+3.3V"
set in1_min 3.3 * 0.95
set in1_max 3.3 * 1.05
compute in1 1.635*@,@/1.635

label in2 "+12V"
set in2_min 12.0 * 0.95
set in2_max 12.0 * 1.05
compute in2 6.0*@,@/6.0

label in3 "+5V"
set in3_min 5.0 * 0.95
set in3_max 5.0 * 1.05
compute in3 2.5*@,@/2.5

label in4 "Vaxg IGD"
set in4_min 0.800
set in4_max 1.000

label in5 "CPU Vcore"
set in5_min 0.750
set in5_max 1.150

label in6 "Dram Voltage"
set in6_min 1.450
set in6_max 1.550

label in7 "3.3 VSB"
set in7_min 3.3 * 0.95
set in7_max 3.3 * 1.05

label in8 "Vbat"

# Other sensor readings
label intrusion0 "Chassis Open"
#set intrusion0_alarm 0


##############################################
chip "acpitz-virtual-0"

ignore temp1
#label temp1 "ACPI Thermal Zone 0 Temp1" # Shows always 27.8

ignore temp2
#label temp2 "ACPI Thermal Zone 0 Temp2" # Shows always 29.8