find-sensor-mibs: Tool for finding MIB structure of sensors on OpenBSD

Description

OpenBSD has a great framework called sysctl that can be used for querying system information and modifying various system settings.

One handy application of sysctl is querying sensor data. Most modern machines have plenty of them, and the sysctl framework provides a single method to query this information.

From the command line, one only has to use sysctl(8) to get the information. From C, OpenBSD provides sysctl(3).

To obtain this information using sysctl(3), one has to know the Message Interface Buffer, or MIB, for the sensor in question. A MIB is nothing more than an array of integers. To find these arrays for each sensor, I wrote find-sensor-mibs.

The following program displays all sensors on the system it is running on along with their current readings and, most importantly, their MIB structure.

Example

On my laptop (a Lenovo T61 running OpenBSD 4.3-release) I have the following output from 'sysctl hw.sensors'

      ryan@barwise# sysctl hw.sensors
      hw.sensors.cpu0.temp0=35.00 degC
      hw.sensors.cpu1.temp0=35.00 degC
      hw.sensors.acpitz0.temp0=47.05 degC (zone temperature)
      hw.sensors.acpitz1.temp0=42.05 degC (zone temperature)
      hw.sensors.acpibat0.volt0=14.40 VDC (voltage)
      hw.sensors.acpibat0.volt1=16.58 VDC (current voltage)
      hw.sensors.acpibat0.watthour0=37.22 Wh (last full capacity)
      hw.sensors.acpibat0.watthour1=1.86 Wh (warning capacity)
      hw.sensors.acpibat0.watthour2=0.20 Wh (low capacity)
      hw.sensors.acpibat0.watthour3=37.22 Wh (remaining capacity), OK
      hw.sensors.acpibat0.raw0=0 (battery full), OK
      hw.sensors.acpibat0.raw1=0 (rate)
      hw.sensors.acpiac0.indicator0=On (power supply)

When running the find-sensor-mibs program, I get the following

      ryan@barwise# ./find-sensor-mibs 

      For reading sensor data via sysctl(3), the MIB structure for each
      sensor on this system is the following:

            mib[] = { CTL_HW, HW_SENSORS, x, y, z } 

      where x, y, and z are as follows:

       x   y   z  sensor name (from sysctl) and raw value
      --- --- --- ---------------------------------------
        0   0   0 hw.sensors.cpu0.temp0 = 309150000
        1   0   0 hw.sensors.cpu1.temp0 = 309150000
        2   0   0 hw.sensors.acpitz0.temp0 = 320200000
        3   0   0 hw.sensors.acpitz1.temp0 = 315200000
        4   2   0 hw.sensors.acpibat0.volt0 = 14400000
        4   2   1 hw.sensors.acpibat0.volt1 = 16584000
        4   7   0 hw.sensors.acpibat0.watthour0 = 37220000
        4   7   1 hw.sensors.acpibat0.watthour1 = 1861000
        4   7   2 hw.sensors.acpibat0.watthour2 = 200000
        4   7   3 hw.sensors.acpibat0.watthour3 = 37220000
        4  10   0 hw.sensors.acpibat0.raw0 = 0
        4  10   1 hw.sensors.acpibat0.raw1 = 0
        5   2   0 hw.sensors.acpibat1.volt0 = 0
        5   2   1 hw.sensors.acpibat1.volt1 = 0
        5   7   0 hw.sensors.acpibat1.watthour0 = 0
        5   7   1 hw.sensors.acpibat1.watthour1 = 0
        5   7   2 hw.sensors.acpibat1.watthour2 = 0
        5   7   3 hw.sensors.acpibat1.watthour3 = 0
        5  10   0 hw.sensors.acpibat1.raw0 = 0
        5  10   1 hw.sensors.acpibat1.raw1 = 0
        6   9   0 hw.sensors.acpiac0.indicator0 = 1

As you can see, sensor MIBs are 5-element integer arrays, where the first 2 elements are CTL_HW and HW_SENSORS, respectively (these are defined constants). The remaining 3 components of each MIB are displayed for each sensor.

Documentation

Installation

Download the source zip below and then simply

tar xvzf find-sensor-mibs.tar.gz
cd find-sensor-mibs
make

Usage

After doing the above, you should simply be able to './find-sensor-mibs' and see a list of all sensors and their associated MIB structures.

Download

Here: find-sensor-mibs.tar.gz.

Notes

This could easily be extended to display the MIB structure for any sysctl. Each first and second level sysctl object, however, has its own structure, so some work would have to be done. None-the-less, The code for the program (all 58 lines) should be more than enough to help out anyone who is curious how to find MIB structures of other sysctl properties.