The mystery of lm-sensors

[Timothy Murphy]

Does anyone understand the output of "sensors"
under the lm-sensors program?

I've been having heat problems with x86_64 Fedora 6
on an Athlon 64 machine (Asus K8V-F motherboard).
The machine runs perfectly under Windows XP and i386 Fedora,
but crashes repeatedly under x86_64 Fedora.

I've come to the pretty firm conclusion
that this is due to overheating,
so I've installed lm-sensors to check the temperature.
Unfortunately I find the output completely incomprehensible,
and none of the documentation I have seen helps much.

Here is the output (under i386 Fedora):
------------------------------------
[tim at blanche ~]$ sensors
w83697hf-isa-0290
Adapter: ISA adapter
VCore:     +1.50 V  (min =  +1.71 V, max =  +1.89 V)       ALARM
+3.3V:     +3.34 V  (min =  +3.14 V, max =  +3.47 V)
+5V:       +5.03 V  (min =  +4.76 V, max =  +5.24 V)
+12V:     +11.07 V  (min = +10.82 V, max = +13.19 V)
-12V:      +0.14 V  (min = -13.18 V, max = -10.80 V)       ALARM
-5V:       +5.10 V  (min =  -5.25 V, max =  -4.75 V)       ALARM
V5SB:      +5.64 V  (min =  +4.76 V, max =  +5.24 V)       ALARM
VBat:      +0.00 V  (min =  +2.40 V, max =  +3.60 V)       ALARM
fan1:        0 RPM  (min =   44 RPM, div = 128)              ALARM
fan2:     1486 RPM  (min = 1506 RPM, div = 4)              ALARM
temp1:       +23°C  (high =   +21°C, hyst =   -72°C)   sensor = thermistor
        ALARM
temp2:     +38.0°C  (high =   +80°C, hyst =   +75°C)   sensor = thermistor
alarms:
beep_enable:
          Sound alarm enabled
------------------------------------

At first sight all those ALARMs seem somewhat frightening,
but then I ran sensors on two machines (PIII and AMD Sempron) 
which seem to have no problems,
and I found a number of ALARMs reported there too:
------------------------------------
[tim at alfred ~]$ sensors
w83781d-i2c-0-2d
Adapter: SMBus PIIX4 adapter at e800

VCore 1:   +1.98 V  (min =  +1.94 V, max =  +2.14 V)
VCore 2:   +1.47 V  (min =  +1.94 V, max =  +2.14 V)       ALARM
+3.3V:     +3.50 V  (min =  +3.14 V, max =  +3.46 V)       ALARM
+5V:       +4.78 V  (min =  +4.73 V, max =  +5.24 V)
+12V:     +11.86 V  (min = +11.37 V, max = +12.59 V)
-12V:     -11.74 V  (min = -12.57 V, max = -11.35 V)
-5V:       -5.06 V  (min =  -5.25 V, max =  -4.74 V)
fan1:        0 RPM  (min = 8437 RPM, div = 4)              ALARM
fan2:     4017 RPM  (min = 3924 RPM, div = 4)
fan3:        0 RPM  (min = 2689 RPM, div = 2)              ALARM
temp1:       +27°C  (high =   -82°C, hyst =   +13°C)
temp2:     -48.0°C  (high =   +70°C, hyst =   +60°C)
temp3:     +29.5°C  (high =   +80°C, hyst =   +75°C)
vid:      +2.050 V  (VRM Version 8.2)
alarms:
beep_enable:
          Sound alarm enabled
------------------------------------
[tim at helen ~]$ sudo sensors
w83697hf-isa-0290
Adapter: ISA adapter
VCore:     +1.41 V  (min =  +1.71 V, max =  +1.89 V)       ALARM
+3.3V:     +3.34 V  (min =  +3.14 V, max =  +3.47 V)
+5V:       +4.97 V  (min =  +4.76 V, max =  +5.24 V)
+12V:     +11.19 V  (min = +10.82 V, max = +13.19 V)
-12V:      +0.55 V  (min = -13.18 V, max = -10.80 V)       ALARM
-5V:       +0.18 V  (min =  -5.25 V, max =  -4.75 V)       ALARM
V5SB:      +5.54 V  (min =  +4.76 V, max =  +5.24 V)       ALARM
VBat:      +2.24 V  (min =  +2.40 V, max =  +3.60 V)       ALARM
fan1:        0 RPM  (min = 2280 RPM, div = 8)              ALARM
fan2:        0 RPM  (min = 14062 RPM, div = 2)              ALARM
temp1:       +31°C  (high =   +71°C, hyst =   -60°C)   sensor = thermistor
temp2:     +33.0°C  (high =   +80°C, hyst =   +75°C)   sensor = thermistor
alarms:   Chassis intrusion detection                      ALARM
beep_enable:
          Sound alarm enabled
------------------------------------

I realise the ALARMs mean the reading is out of the specified range,
but who sets these ranges?
Some of them seem absurd eg high=-82C for temp1.

Incidentally, I gather that "hyst" stands for hysterisis,
but what on earth does that mean in this context?

And (finally) how does one tell what the different "temp" refer to?




-- 
Timothy Murphy  
e-mail (<80k only): tim /at/ birdsnest.maths.tcd.ie
tel: +353-86-2336090, +353-1-2842366
s-mail: School of Mathematics, Trinity College, Dublin 2, Ireland