# 8 Sensor

Each sensor chip gets its own directory in the sysfs /sys/devices tree.
To find all sensor chips, it is easier to follow the device symlinks
from /sys/class/hwmon/hwmon\*, where \* is a real number (0,1,2,...).

The sensor readings are located either in /sys/class/hwmon/hwmon\*/
directory for virtual devices, or in /sys/class/hwmon/hwmon\*/device
directory for non-virtual devices. A file, called name, located inside
hwmon\* or hwmon\*/device directories contains the name of the chip,
which corresponds to the name of the kernel driver used by the sensor
chip.

There is only one sensor reading value per file. The common scheme for
naming the files that contain sensor readings inside any of the
directories mentioned above is:
<type><number>\_<item>, where

-   **type** - for sensor chips is "in" (voltage), "temp" (temperature),
    "fan" (fan), etc.,
-   **item** - "input" (measured value), "max" (high threshold), "min"
    (low threshold), etc.,
-   **number** - always used for elements that can be present more than
    once (usually starts from 1, except for voltages which start from
    0). If files do not refer to a specific element they have a simple
    name with no number.

The information regarding sensors available on the host can be acquired
using **sensor-detect** and **sensors** tools (lm-sensors package:
<http://lm-sensors.org/>). **Sensors-detect** helps to determine which
modules are necessary for available sensors. When modules are loaded the
**sensors** program can be used to show the readings of all sensor
chips. The labeling of sensor readings, used by this program, can be
different from the common naming scheme
(<type><number>\_<item> ):

-   if there is a file called <type><number>\_label, then
    the label inside this file will be used instead of
    <type><number><item> name;
-   if there is no <type><number>\_label file, then the
    program searches inside the /etc/sensors.conf (could be also
    /etc/sensors3.conf, or different) for the name substitution.

This labeling allows user to determine what kind of hardware is used. If
there is neither <type><number>\_label file nor label inside
the configuration file the type of hardware can be determined by the
name attribute (hwmon\*/device/name). The actual names of sensors, which
zabbix\_agent accepts, can be obtained by running **sensors** program
with -u parameter (**sensors -u**).

In **sensor** program the available sensors are separated by the bus
type (ISA adapter, PCI adapter, SPI adapter, Virtual device, ACPI
interface, HID adapter).

##### On Linux 2.4:

(Sensor readings are obtained from /proc/sys/dev/sensors directory)

-   **device** - device name (if <mode> is used, it is a regular
    expression);
-   **sensor** - sensor name (if <mode> is used, it is a regular
    expression);
-   **mode** - possible values: avg, max, min (if this parameter is
    omitted, device and sensor are treated verbatim).

Example key: sensor\[w83781d-i2c-0-2d,temp1\]

Prior to Zabbix 1.8.4, the sensor\[temp1\] format was used.

##### On Linux 2.6+:

(Sensor readings are obtained from /sys/class/hwmon directory)

-   **device** - device name (non regular expression). The device name
    could be the actual name of the device (e.g 0000:00:18.3) or the
    name acquired using sensors program (e.g. k8temp-pci-00c3). It is up
    to the user to choose which name to use;
-   **sensor** - sensor name (non regular expression);
-   **mode** - possible values: avg, max, min (if this parameter is
    omitted, device and sensor are treated verbatim).

Example key:

sensor\[k8temp-pci-00c3,temp,max\] or sensor\[0000:00:18.3,temp1\]

sensor\[smsc47b397-isa-0880,in,avg\] or sensor\[smsc47b397.2176,in1\]

#### Obtaining sensor names

Sensor labels, as printed by the *sensors* command, cannot always be
used directly because the naming of labels may be different for each
sensor chip vendor. For example, *sensors* output might contain the
following lines:

    $ sensors
    in0:         +2.24 V  (min =  +0.00 V, max =  +3.32 V)   
    Vcore:       +1.15 V  (min =  +0.00 V, max =  +2.99 V)   
    +3.3V:       +3.30 V  (min =  +2.97 V, max =  +3.63 V)   
    +12V:       +13.00 V  (min =  +0.00 V, max = +15.94 V)
    M/B Temp:    +30.0°C  (low  = -127.0°C, high = +127.0°C)

Out of these, only one label may be used directly:

    $ zabbix_get -s 127.0.0.1 -k sensor[lm85-i2c-0-2e,in0]
    2.240000

Attempting to use other labels (like *Vcore* or *+12V*) will not work.

    $ zabbix_get -s 127.0.0.1 -k sensor[lm85-i2c-0-2e,Vcore]
    ZBX_NOTSUPPORTED

To find out the actual sensor name, which can be used by Zabbix to
retrieve the sensor readings, run *sensors -u*. In the output, the
following may be observed:

    $ sensors -u
    ...
    Vcore:
      in1_input: 1.15
      in1_min: 0.00
      in1_max: 2.99
      in1_alarm: 0.00
    ...    
    +12V:
      in4_input: 13.00
      in4_min: 0.00
      in4_max: 15.94
      in4_alarm: 0.00
    ...

So *Vcore* should be queried as *in1*, and *+12V* should be queried as
*in4*.[^1]

    $ zabbix_get -s 127.0.0.1 -k sensor[lm85-i2c-0-2e,in1]
    1.301000

Not only voltage (in), but also current (curr), temperature (temp) and
fan speed (fan) readings can be retrieved by Zabbix.

[^1]: According to
    [specification](https://www.kernel.org/doc/Documentation/hwmon/sysfs-interface)
    these are voltages on chip pins and generally speaking may need
    scaling.