path: root/Documentation/hwmon/sysfs-interface

Naming and data format standards for sysfs files
------------------------------------------------

The libsensors library offers an interface to the raw sensors data
through the sysfs interface. See libsensors documentation and source for
more further information. As of writing this document, libsensors
(from lm_sensors 2.8.3) is heavily chip-dependant. Adding or updating
support for any given chip requires modifying the library's code.
This is because libsensors was written for the procfs interface
older kernel modules were using, which wasn't standardized enough.
Recent versions of libsensors (from lm_sensors 2.8.2 and later) have
support for the sysfs interface, though.

The new sysfs interface was designed to be as chip-independant as
possible.

Note that motherboards vary widely in the connections to sensor chips.
There is no standard that ensures, for example, that the second
temperature sensor is connected to the CPU, or that the second fan is on
the CPU. Also, some values reported by the chips need some computation
before they make full sense. For example, most chips can only measure
voltages between 0 and +4V. Other voltages are scaled back into that
range using external resistors. Since the values of these resistors
can change from motherboard to motherboard, the conversions cannot be
hard coded into the driver and have to be done in user space.

For this reason, even if we aim at a chip-independant libsensors, it will
still require a configuration file (e.g. /etc/sensors.conf) for proper
values conversion, labeling of inputs and hiding of unused inputs.

An alternative method that some programs use is to access the sysfs
files directly. This document briefly describes the standards that the
drivers follow, so that an application program can scan for entries and
access this data in a simple and consistent way. That said, such programs
will have to implement conversion, labeling and hiding of inputs. For
this reason, it is still not recommended to bypass the library.

If you are developing a userspace application please send us feedback on
this standard.

Note that this standard isn't completely established yet, so it is subject
to changes, even important ones. One more reason to use the library instead
of accessing sysfs files directly.

Each chip gets its own directory in the sysfs /sys/devices tree.  To
find all sensor chips, it is easier to follow the symlinks from
/sys/i2c/devices/

All sysfs values are fixed point numbers.  To get the true value of some
of the values, you should divide by the specified value.

There is only one value per file, unlike the older /proc specification.
The common scheme for files naming is: <type><number>_<item>. Usual
types for sensor chips are "in" (voltage), "temp" (temperature) and
"fan" (fan). Usual items are "input" (measured value), "max" (high
threshold, "min" (low threshold). Numbering usually starts from 1,
except for voltages which start from 0 (because most data sheets use
this). A number is always used for elements that can be present more
than once, even if there is a single element of the given type on the
specific chip. Other files do not refer to a specific element, so
they have a simple name, and no number.

Alarms are direct indications read from the chips. The drivers do NOT
make comparisons of readings to thresholds. This allows violations
between readings to be caught and alarmed. The exact definition of an
alarm (for example, whether a threshold must be met or must be exceeded
to cause an alarm) is chip-dependent.


-------------------------------------------------------------------------

[0-*]	denotes any positive number starting from 0
[1-*]	denotes any positive number starting from 1
RO	read only value
RW	read/write value

Read/write values may be read-only for some chips, depending on the
hardware implementation.

************
* Voltages *
************

in[0-*]_min	Voltage min value.
		Unit: millivolt
		RW
		
in[0-*]_max	Voltage max value.
		Unit: millivolt
		RW
		
in[0-*]_input	Voltage input value.
		Unit: millivolt
		RO
		Voltage measured on the chip pin.
		Actual voltage depends on the scaling resistors on the
		motherboard, as recommended in the chip datasheet.
		This varies by chip and by motherboard.
		Because of this variation, values are generally NOT scaled
		by the chip driver, and must be done by the application.
		However, some drivers (notably lm87 and via686a)
		do scale, because of internal resistors built into a chip.
		These drivers will output the actual voltage.

		Typical usage:
			in0_*	CPU #1 voltage (not scaled)
			in1_*	CPU #2 voltage (not scaled)
			in2_*	3.3V nominal (not scaled)
			in3_*	5.0V nominal (scaled)
			in4_*	12.0V nominal (scaled)
			in5_*	-12.0V nominal (scaled)
			in6_*	-5.0V nominal (scaled)
			in7_*	varies
			in8_*	varies

cpu[0-*]_vid	CPU core reference voltage.
		Unit: millivolt
		RO
		Not always correct.

vrm		Voltage Regulator Module version number. 
		RW (but changing it should no more be necessary)
		Originally the VRM standard version multiplied by 10, but now
		an arbitrary number, as not all standards have a version
		number.
		Affects the way the driver calculates the CPU core reference
		voltage from the vid pins.

Also see the Alarms section for status flags associated with voltages.


********
* Fans *
********

fan[1-*]_min	Fan minimum value
		Unit: revolution/min (RPM)
		RW

fan[1-*]_input	Fan input value.
		Unit: revolution/min (RPM)
		RO

fan[1-*]_div	Fan divisor.
		Integer value in powers of two (1, 2, 4, 8, 16, 32, 64, 128).
		RW
		Some chips only support values 1, 2, 4 and 8.
		Note that this is actually an internal clock divisor, which
		affects the measurable speed range, not the read value.

Also see the Alarms section for status flags associated with fans.


*******
* PWM *
*******

pwm[1-*]	Pulse width modulation fan control.
		Integer value in the range 0 to 255
		RW
		255 is max or 100%.

pwm[1-*]_enable
		Switch PWM on and off.
		Not always present even if fan*_pwm is.
		0: turn off
		1: turn on in manual mode
		2+: turn on in automatic mode
		Check individual chip documentation files for automatic mode details.
		RW

pwm[1-*]_mode
		0: DC mode
		1: PWM mode
		RW

pwm[1-*]_auto_channels_temp
		Select which temperature channels affect this PWM output in
		auto mode. Bitfield, 1 is temp1, 2 is temp2, 4 is temp3 etc...
		Which values are possible depend on the chip used.
		RW

pwm[1-*]_auto_point[1-*]_pwm
pwm[1-*]_auto_point[1-*]_temp
pwm[1-*]_auto_point[1-*]_temp_hyst
		Define the PWM vs temperature curve. Number of trip points is
		chip-dependent. Use this for chips which associate trip points
		to PWM output channels.
		RW

OR

temp[1-*]_auto_point[1-*]_pwm
temp[1-*]_auto_point[1-*]_temp
temp[1-*]_auto_point[1-*]_temp_hyst
		Define the PWM vs temperature curve. Number of trip points is
		chip-dependent. Use this for chips which associate trip points
		to temperature channels.
		RW


****************
* Temperatures *
****************

temp[1-*]_type	Sensor type selection.
		Integers 1 to 4 or thermistor Beta value (typically 3435)
		RW
		1: PII/Celeron Diode
		2: 3904 transistor
		3: thermal diode
		4: thermistor (default/unknown Beta)
		Not all types are supported by all chips

temp[1-*]_max	Temperature max value.
		Unit: millidegree Celcius
		RW

temp[1-*]_min	Temperature min value.
		Unit: millidegree Celcius
		RW

temp[1-*]_max_hyst
		Temperature hysteresis value for max limit.
		Unit: millidegree Celcius
		Must be reported as an absolute temperature, NOT a delta
		from the max value.
		RW

temp[1-*]_input Temperature input value.
		Unit: millidegree Celcius
		RO

temp[1-*]_crit	Temperature critical value, typically greater than
		corresponding temp_max values.
		Unit: millidegree Celcius
		RW

temp[1-*]_crit_hyst
		Temperature hysteresis value for critical limit.
		Unit: millidegree Celcius
		Must be reported as an absolute temperature, NOT a delta
		from the critical value.
		RW

temp[1-4]_offset
		Temperature offset which is added to the temperature reading
		by the chip.
		Unit: millidegree Celsius
		Read/Write value.

		If there are multiple temperature sensors, temp1_* is
		generally the sensor inside the chip itself,
		reported as "motherboard temperature".  temp2_* to
		temp4_* are generally sensors external to the chip
		itself, for example the thermal diode inside the CPU or
		a thermistor nearby.

Also see the Alarms section for status flags associated with temperatures.


************
* Currents *
************

Note that no known chip provides current measurements as of writing,
so this part is theoretical, so to say.

curr[1-*]_max	Current max value
		Unit: milliampere
		RW

curr[1-*]_min	Current min value.
		Unit: milliampere
		RW

curr[1-*]_input	Current input value
		Unit: milliampere
		RO


**********
* Alarms *
**********

Each channel or limit may have an associated alarm file, containing a
boolean value. 1 means than an alarm condition exists, 0 means no alarm.

Usually a given chip will either use channel-related alarms, or
limit-related alarms, not both. The driver should just reflect the hardware
implementation.

in[0-*]_alarm
fan[1-*]_alarm
temp[1-*]_alarm
		Channel alarm
		0: no alarm
		1: alarm
		RO

OR

in[0-*]_min_alarm
in[0-*]_max_alarm
fan[1-*]_min_alarm
temp[1-*]_min_alarm
temp[1-*]_max_alarm
temp[1-*]_crit_alarm
		Limit alarm
		0: no alarm
		1: alarm
		RO

Each input channel may have an associated fault file. This can be used
to notify open diodes, unconnected fans etc. where the hardware
supports it. When this boolean has value 1, the measurement for that
channel should not be trusted.

in[0-*]_input_fault
fan[1-*]_input_fault
temp[1-*]_input_fault
		Input fault condition
		0: no fault occured
		1: fault condition
		RO

Some chips also offer the possibility to get beeped when an alarm occurs:

beep_enable	Master beep enable
		0: no beeps
		1: beeps
		RW

in[0-*]_beep
fan[1-*]_beep
temp[1-*]_beep
		Channel beep
		0: disable
		1: enable
		RW

In theory, a chip could provide per-limit beep masking, but no such chip
was seen so far.

Old drivers provided a different, non-standard interface to alarms and
beeps. These interface files are deprecated, but will be kept around
for compatibility reasons:

alarms		Alarm bitmask.
		RO
		Integer representation of one to four bytes.
		A '1' bit means an alarm.
		Chips should be programmed for 'comparator' mode so that
		the alarm will 'come back' after you read the register
		if it is still valid.
		Generally a direct representation of a chip's internal
		alarm registers; there is no standard for the position
		of individual bits. For this reason, the use of this
		interface file for new drivers is discouraged. Use
		individual *_alarm and *_fault files instead.
		Bits are defined in kernel/include/sensors.h.

beep_mask	Bitmask for beep.
		Same format as 'alarms' with the same bit locations,
		use discouraged for the same reason. Use individual
		*_beep files instead.
		RW


*********
* Other *
*********

eeprom		Raw EEPROM data in binary form.
		RO

pec		Enable or disable PEC (SMBus only)
		0: disable
		1: enable
		RW