1 Naming and data format standards for sysfs files
2 ------------------------------------------------
4 The libsensors library offers an interface to the raw sensors data
5 through the sysfs interface. See libsensors documentation and source for
6 further information. As of writing this document, libsensors
7 (from lm_sensors 2.8.3) is heavily chip-dependent. Adding or updating
8 support for any given chip requires modifying the library's code.
9 This is because libsensors was written for the procfs interface
10 older kernel modules were using, which wasn't standardized enough.
11 Recent versions of libsensors (from lm_sensors 2.8.2 and later) have
12 support for the sysfs interface, though.
14 The new sysfs interface was designed to be as chip-independent as
17 Note that motherboards vary widely in the connections to sensor chips.
18 There is no standard that ensures, for example, that the second
19 temperature sensor is connected to the CPU, or that the second fan is on
20 the CPU. Also, some values reported by the chips need some computation
21 before they make full sense. For example, most chips can only measure
22 voltages between 0 and +4V. Other voltages are scaled back into that
23 range using external resistors. Since the values of these resistors
24 can change from motherboard to motherboard, the conversions cannot be
25 hard coded into the driver and have to be done in user space.
27 For this reason, even if we aim at a chip-independent libsensors, it will
28 still require a configuration file (e.g. /etc/sensors.conf) for proper
29 values conversion, labeling of inputs and hiding of unused inputs.
31 An alternative method that some programs use is to access the sysfs
32 files directly. This document briefly describes the standards that the
33 drivers follow, so that an application program can scan for entries and
34 access this data in a simple and consistent way. That said, such programs
35 will have to implement conversion, labeling and hiding of inputs. For
36 this reason, it is still not recommended to bypass the library.
38 If you are developing a userspace application please send us feedback on
41 Note that this standard isn't completely established yet, so it is subject
42 to changes. If you are writing a new hardware monitoring driver those
43 features can't seem to fit in this interface, please contact us with your
44 extension proposal. Keep in mind that backward compatibility must be
47 Each chip gets its own directory in the sysfs /sys/devices tree. To
48 find all sensor chips, it is easier to follow the device symlinks from
49 /sys/class/hwmon/hwmon*.
51 All sysfs values are fixed point numbers.
53 There is only one value per file, unlike the older /proc specification.
54 The common scheme for files naming is: <type><number>_<item>. Usual
55 types for sensor chips are "in" (voltage), "temp" (temperature) and
56 "fan" (fan). Usual items are "input" (measured value), "max" (high
57 threshold, "min" (low threshold). Numbering usually starts from 1,
58 except for voltages which start from 0 (because most data sheets use
59 this). A number is always used for elements that can be present more
60 than once, even if there is a single element of the given type on the
61 specific chip. Other files do not refer to a specific element, so
62 they have a simple name, and no number.
64 Alarms are direct indications read from the chips. The drivers do NOT
65 make comparisons of readings to thresholds. This allows violations
66 between readings to be caught and alarmed. The exact definition of an
67 alarm (for example, whether a threshold must be met or must be exceeded
68 to cause an alarm) is chip-dependent.
71 -------------------------------------------------------------------------
73 [0-*] denotes any positive number starting from 0
74 [1-*] denotes any positive number starting from 1
78 Read/write values may be read-only for some chips, depending on the
79 hardware implementation.
81 All entries are optional, and should only be created in a given driver
82 if the chip has the feature.
88 in[0-*]_min Voltage min value.
92 in[0-*]_max Voltage max value.
96 in[0-*]_input Voltage input value.
99 Voltage measured on the chip pin.
100 Actual voltage depends on the scaling resistors on the
101 motherboard, as recommended in the chip datasheet.
102 This varies by chip and by motherboard.
103 Because of this variation, values are generally NOT scaled
104 by the chip driver, and must be done by the application.
105 However, some drivers (notably lm87 and via686a)
106 do scale, because of internal resistors built into a chip.
107 These drivers will output the actual voltage.
110 in0_* CPU #1 voltage (not scaled)
111 in1_* CPU #2 voltage (not scaled)
112 in2_* 3.3V nominal (not scaled)
113 in3_* 5.0V nominal (scaled)
114 in4_* 12.0V nominal (scaled)
115 in5_* -12.0V nominal (scaled)
116 in6_* -5.0V nominal (scaled)
120 cpu[0-*]_vid CPU core reference voltage.
125 vrm Voltage Regulator Module version number.
126 RW (but changing it should no more be necessary)
127 Originally the VRM standard version multiplied by 10, but now
128 an arbitrary number, as not all standards have a version
130 Affects the way the driver calculates the CPU core reference
131 voltage from the vid pins.
133 Also see the Alarms section for status flags associated with voltages.
140 fan[1-*]_min Fan minimum value
141 Unit: revolution/min (RPM)
144 fan[1-*]_input Fan input value.
145 Unit: revolution/min (RPM)
148 fan[1-*]_div Fan divisor.
149 Integer value in powers of two (1, 2, 4, 8, 16, 32, 64, 128).
151 Some chips only support values 1, 2, 4 and 8.
152 Note that this is actually an internal clock divisor, which
153 affects the measurable speed range, not the read value.
155 Also see the Alarms section for status flags associated with fans.
162 pwm[1-*] Pulse width modulation fan control.
163 Integer value in the range 0 to 255
168 Switch PWM on and off.
169 Not always present even if fan*_pwm is.
171 1: turn on in manual mode
172 2+: turn on in automatic mode
173 Check individual chip documentation files for automatic mode details.
181 pwm[1-*]_auto_channels_temp
182 Select which temperature channels affect this PWM output in
183 auto mode. Bitfield, 1 is temp1, 2 is temp2, 4 is temp3 etc...
184 Which values are possible depend on the chip used.
187 pwm[1-*]_auto_point[1-*]_pwm
188 pwm[1-*]_auto_point[1-*]_temp
189 pwm[1-*]_auto_point[1-*]_temp_hyst
190 Define the PWM vs temperature curve. Number of trip points is
191 chip-dependent. Use this for chips which associate trip points
192 to PWM output channels.
197 temp[1-*]_auto_point[1-*]_pwm
198 temp[1-*]_auto_point[1-*]_temp
199 temp[1-*]_auto_point[1-*]_temp_hyst
200 Define the PWM vs temperature curve. Number of trip points is
201 chip-dependent. Use this for chips which associate trip points
202 to temperature channels.
210 temp[1-*]_type Sensor type selection.
211 Integers 1 to 6 or thermistor Beta value (typically 3435)
216 4: thermistor (default/unknown Beta)
219 Not all types are supported by all chips
221 temp[1-*]_max Temperature max value.
222 Unit: millidegree Celsius (or millivolt, see below)
225 temp[1-*]_min Temperature min value.
226 Unit: millidegree Celsius
230 Temperature hysteresis value for max limit.
231 Unit: millidegree Celsius
232 Must be reported as an absolute temperature, NOT a delta
236 temp[1-*]_input Temperature input value.
237 Unit: millidegree Celsius
240 temp[1-*]_crit Temperature critical value, typically greater than
241 corresponding temp_max values.
242 Unit: millidegree Celsius
246 Temperature hysteresis value for critical limit.
247 Unit: millidegree Celsius
248 Must be reported as an absolute temperature, NOT a delta
249 from the critical value.
253 Temperature offset which is added to the temperature reading
255 Unit: millidegree Celsius
258 If there are multiple temperature sensors, temp1_* is
259 generally the sensor inside the chip itself,
260 reported as "motherboard temperature". temp2_* to
261 temp4_* are generally sensors external to the chip
262 itself, for example the thermal diode inside the CPU or
265 Some chips measure temperature using external thermistors and an ADC, and
266 report the temperature measurement as a voltage. Converting this voltage
267 back to a temperature (or the other way around for limits) requires
268 mathematical functions not available in the kernel, so the conversion
269 must occur in user space. For these chips, all temp* files described
270 above should contain values expressed in millivolt instead of millidegree
271 Celsius. In other words, such temperature channels are handled as voltage
272 channels by the driver.
274 Also see the Alarms section for status flags associated with temperatures.
281 Note that no known chip provides current measurements as of writing,
282 so this part is theoretical, so to say.
284 curr[1-*]_max Current max value
288 curr[1-*]_min Current min value.
292 curr[1-*]_input Current input value
301 Each channel or limit may have an associated alarm file, containing a
302 boolean value. 1 means than an alarm condition exists, 0 means no alarm.
304 Usually a given chip will either use channel-related alarms, or
305 limit-related alarms, not both. The driver should just reflect the hardware
329 Each input channel may have an associated fault file. This can be used
330 to notify open diodes, unconnected fans etc. where the hardware
331 supports it. When this boolean has value 1, the measurement for that
332 channel should not be trusted.
336 temp[1-*]_input_fault
337 Input fault condition
342 Some chips also offer the possibility to get beeped when an alarm occurs:
344 beep_enable Master beep enable
357 In theory, a chip could provide per-limit beep masking, but no such chip
360 Old drivers provided a different, non-standard interface to alarms and
361 beeps. These interface files are deprecated, but will be kept around
362 for compatibility reasons:
364 alarms Alarm bitmask.
366 Integer representation of one to four bytes.
367 A '1' bit means an alarm.
368 Chips should be programmed for 'comparator' mode so that
369 the alarm will 'come back' after you read the register
370 if it is still valid.
371 Generally a direct representation of a chip's internal
372 alarm registers; there is no standard for the position
373 of individual bits. For this reason, the use of this
374 interface file for new drivers is discouraged. Use
375 individual *_alarm and *_fault files instead.
376 Bits are defined in kernel/include/sensors.h.
378 beep_mask Bitmask for beep.
379 Same format as 'alarms' with the same bit locations,
380 use discouraged for the same reason. Use individual
381 *_beep files instead.
389 eeprom Raw EEPROM data in binary form.
392 pec Enable or disable PEC (SMBus only)
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