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My computer is restarting unexpectedly for some days. First I though Its an os issue. I gone through all the sys log and didn't find any clue. Then gone through bios event log. Nothing was there too. Then at the hardware monitor section I saw CPU Thermal margin is very low. Like 1°-3° celsius. And CPU temperature (ICS Temp) is about 83°-86°

After googling a bit I found temperature margin seems like a margin that CPU is not designed to operate if temperature goes beyond it.
So I though I would monitor this. But couldn't find any tool on Ubuntu 12.04.

So,

  1. How do I reduce CPU temperature? I have already cleaned all the pc component. All fans are functional?
  2. How do I monitor CPU temperature? All the temperature monitor applet I found monitors M/B temperature. All of them shows temperature 54°. which I see is M/B temp on BIOS. But CPU is more than 80° on BIOS?
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Monitoring/Getting current temperature

The classic tool for this kind of monitoring under Linux is sensors:

sudo apt-get install lm-sensors
sudo sensors-detect

Answer "y" to all questions and load any modules suggested by the last step using (sudo modprobe module_name), make sure the settings are loaded and then then run sensors:

sensors

That should show you output similar to this:

$ sensors
coretemp-isa-0000
Adapter: ISA adapter
Core 0:       +53.0°C  (high = +95.0°C, crit = +105.0°C)
Core 2:       +58.0°C  (high = +95.0°C, crit = +105.0°C)

i8k-virtual-0
Adapter: Virtual device
Right Fan:   87690 RPM
CPU:          +58.0°C  

Depending on your system, there are various files that can contain this information. One of these should give you your temperature:

cat /sys/devices/platform/coretemp.0/temp?_input

or

cat /proc/acpi/thermal_zone/THM0/temperature

or

cat /sys/kernel/debug/ips/cpu_temp

or

cat /sys/devices/virtual/hwmon/hwmon1/temp1_input 

or

cat cat /sys/bus/platform/devices/coretemp.0/temp2_input

Reducing CPU temperature.

  1. Is your CPU always running at top speed? Try setting another scaling governor. Your options are:

    • Performance keeps the CPU at the highest possible frequency
    • Powersave keeps the CPU at the lowest possible frequency
    • Userspace exports the available frequency information to the user level (through the /sys file system) and permits user-space control of the CPU frequency
    • Ondemand scales the CPU frequencies according to the CPU usage (like does the userspace frequency scaling daemons, but in kernel)
    • Conservative acts like the ondemand but increases frequency step by step

    Personally, I use ondemand and recommend it. The Ubuntu wiki warns of certain problems, but I have never had any trouble with it. To use the ondemand governor do:

    sudo echo ondemand > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor

  2. If the above does not help, you might have a hardware issue. Since you have already checked the fan, the next most likely culprit is the thermal paste. If you've had your computer for a while, it is likely that the paste between the heat sink and the CPU has gotten old and you should change it:

    • Open the machine, remove the fan and heatsink from the CPU.
    • Remove the old thermal paste from both the CPU and the heatsink, ideally using a cotton swab with isopropyl alcohol. For the heatsink, you can also use a knife or similar to scrape off the paste before cleaning the rest with the alcohol. I don't recommend you try and scrape it off the CPU though, just use the cotton swab.
    • Once you have cleaned the old paste away, apply a small amount to the center of the CPU and then re-attache the heatsink. Since the heatsink will be held down tightly against the CPU, it will also spread the paste around uniformly. Make sure you don't use a lot of paste since that might cause it to overflow around the edges of the heatsink.

    For a (very) detailed tutorial on changing your thermal paste, see here.

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