1Naming and data format standards for sysfs files
2------------------------------------------------
3
4The libsensors library offers an interface to the raw sensors data
5through the sysfs interface. Since lm-sensors 3.0.0, libsensors is
6completely chip-independent. It assumes that all the kernel drivers
7implement the standard sysfs interface described in this document.
8This makes adding or updating support for any given chip very easy, as
9libsensors, and applications using it, do not need to be modified.
10This is a major improvement compared to lm-sensors 2.
11
12Note that motherboards vary widely in the connections to sensor chips.
13There is no standard that ensures, for example, that the second
14temperature sensor is connected to the CPU, or that the second fan is on
15the CPU. Also, some values reported by the chips need some computation
16before they make full sense. For example, most chips can only measure
17voltages between 0 and +4V. Other voltages are scaled back into that
18range using external resistors. Since the values of these resistors
19can change from motherboard to motherboard, the conversions cannot be
20hard coded into the driver and have to be done in user space.
21
22For this reason, even if we aim at a chip-independent libsensors, it will
23still require a configuration file (e.g. /etc/sensors.conf) for proper
24values conversion, labeling of inputs and hiding of unused inputs.
25
26An alternative method that some programs use is to access the sysfs
27files directly. This document briefly describes the standards that the
28drivers follow, so that an application program can scan for entries and
29access this data in a simple and consistent way. That said, such programs
30will have to implement conversion, labeling and hiding of inputs. For
31this reason, it is still not recommended to bypass the library.
32
33Each chip gets its own directory in the sysfs /sys/devices tree.  To
34find all sensor chips, it is easier to follow the device symlinks from
35/sys/class/hwmon/hwmon*.
36
37Up to lm-sensors 3.0.0, libsensors looks for hardware monitoring attributes
38in the "physical" device directory. Since lm-sensors 3.0.1, attributes found
39in the hwmon "class" device directory are also supported. Complex drivers
40(e.g. drivers for multifunction chips) may want to use this possibility to
41avoid namespace pollution. The only drawback will be that older versions of
42libsensors won't support the driver in question.
43
44All sysfs values are fixed point numbers.
45
46There is only one value per file, unlike the older /proc specification.
47The common scheme for files naming is: <type><number>_<item>. Usual
48types for sensor chips are "in" (voltage), "temp" (temperature) and
49"fan" (fan). Usual items are "input" (measured value), "max" (high
50threshold, "min" (low threshold). Numbering usually starts from 1,
51except for voltages which start from 0 (because most data sheets use
52this). A number is always used for elements that can be present more
53than once, even if there is a single element of the given type on the
54specific chip. Other files do not refer to a specific element, so
55they have a simple name, and no number.
56
57Alarms are direct indications read from the chips. The drivers do NOT
58make comparisons of readings to thresholds. This allows violations
59between readings to be caught and alarmed. The exact definition of an
60alarm (for example, whether a threshold must be met or must be exceeded
61to cause an alarm) is chip-dependent.
62
63When setting values of hwmon sysfs attributes, the string representation of
64the desired value must be written, note that strings which are not a number
65are interpreted as 0! For more on how written strings are interpreted see the
66"sysfs attribute writes interpretation" section at the end of this file.
67
68-------------------------------------------------------------------------
69
70[0-*]	denotes any positive number starting from 0
71[1-*]	denotes any positive number starting from 1
72RO	read only value
73WO	write only value
74RW	read/write value
75
76Read/write values may be read-only for some chips, depending on the
77hardware implementation.
78
79All entries (except name) are optional, and should only be created in a
80given driver if the chip has the feature.
81
82
83*********************
84* Global attributes *
85*********************
86
87name		The chip name.
88		This should be a short, lowercase string, not containing
89		spaces nor dashes, representing the chip name. This is
90		the only mandatory attribute.
91		I2C devices get this attribute created automatically.
92		RO
93
94update_interval	The interval at which the chip will update readings.
95		Unit: millisecond
96		RW
97		Some devices have a variable update rate or interval.
98		This attribute can be used to change it to the desired value.
99
100
101************
102* Voltages *
103************
104
105in[0-*]_min	Voltage min value.
106		Unit: millivolt
107		RW
108		
109in[0-*]_lcrit	Voltage critical min value.
110		Unit: millivolt
111		RW
112		If voltage drops to or below this limit, the system may
113		take drastic action such as power down or reset. At the very
114		least, it should report a fault.
115
116in[0-*]_max	Voltage max value.
117		Unit: millivolt
118		RW
119		
120in[0-*]_crit	Voltage critical max value.
121		Unit: millivolt
122		RW
123		If voltage reaches or exceeds this limit, the system may
124		take drastic action such as power down or reset. At the very
125		least, it should report a fault.
126
127in[0-*]_input	Voltage input value.
128		Unit: millivolt
129		RO
130		Voltage measured on the chip pin.
131		Actual voltage depends on the scaling resistors on the
132		motherboard, as recommended in the chip datasheet.
133		This varies by chip and by motherboard.
134		Because of this variation, values are generally NOT scaled
135		by the chip driver, and must be done by the application.
136		However, some drivers (notably lm87 and via686a)
137		do scale, because of internal resistors built into a chip.
138		These drivers will output the actual voltage. Rule of
139		thumb: drivers should report the voltage values at the
140		"pins" of the chip.
141
142in[0-*]_average
143		Average voltage
144		Unit: millivolt
145		RO
146
147in[0-*]_lowest
148		Historical minimum voltage
149		Unit: millivolt
150		RO
151
152in[0-*]_highest
153		Historical maximum voltage
154		Unit: millivolt
155		RO
156
157in[0-*]_reset_history
158		Reset inX_lowest and inX_highest
159		WO
160
161in_reset_history
162		Reset inX_lowest and inX_highest for all sensors
163		WO
164
165in[0-*]_label	Suggested voltage channel label.
166		Text string
167		Should only be created if the driver has hints about what
168		this voltage channel is being used for, and user-space
169		doesn't. In all other cases, the label is provided by
170		user-space.
171		RO
172
173cpu[0-*]_vid	CPU core reference voltage.
174		Unit: millivolt
175		RO
176		Not always correct.
177
178vrm		Voltage Regulator Module version number. 
179		RW (but changing it should no more be necessary)
180		Originally the VRM standard version multiplied by 10, but now
181		an arbitrary number, as not all standards have a version
182		number.
183		Affects the way the driver calculates the CPU core reference
184		voltage from the vid pins.
185
186Also see the Alarms section for status flags associated with voltages.
187
188
189********
190* Fans *
191********
192
193fan[1-*]_min	Fan minimum value
194		Unit: revolution/min (RPM)
195		RW
196
197fan[1-*]_max	Fan maximum value
198		Unit: revolution/min (RPM)
199		Only rarely supported by the hardware.
200		RW
201
202fan[1-*]_input	Fan input value.
203		Unit: revolution/min (RPM)
204		RO
205
206fan[1-*]_div	Fan divisor.
207		Integer value in powers of two (1, 2, 4, 8, 16, 32, 64, 128).
208		RW
209		Some chips only support values 1, 2, 4 and 8.
210		Note that this is actually an internal clock divisor, which
211		affects the measurable speed range, not the read value.
212
213fan[1-*]_pulses	Number of tachometer pulses per fan revolution.
214		Integer value, typically between 1 and 4.
215		RW
216		This value is a characteristic of the fan connected to the
217		device's input, so it has to be set in accordance with the fan
218		model.
219		Should only be created if the chip has a register to configure
220		the number of pulses. In the absence of such a register (and
221		thus attribute) the value assumed by all devices is 2 pulses
222		per fan revolution.
223
224fan[1-*]_target
225		Desired fan speed
226		Unit: revolution/min (RPM)
227		RW
228		Only makes sense if the chip supports closed-loop fan speed
229		control based on the measured fan speed.
230
231fan[1-*]_label	Suggested fan channel label.
232		Text string
233		Should only be created if the driver has hints about what
234		this fan channel is being used for, and user-space doesn't.
235		In all other cases, the label is provided by user-space.
236		RO
237
238Also see the Alarms section for status flags associated with fans.
239
240
241*******
242* PWM *
243*******
244
245pwm[1-*]	Pulse width modulation fan control.
246		Integer value in the range 0 to 255
247		RW
248		255 is max or 100%.
249
250pwm[1-*]_enable
251		Fan speed control method:
252		0: no fan speed control (i.e. fan at full speed)
253		1: manual fan speed control enabled (using pwm[1-*])
254		2+: automatic fan speed control enabled
255		Check individual chip documentation files for automatic mode
256		details.
257		RW
258
259pwm[1-*]_mode	0: DC mode (direct current)
260		1: PWM mode (pulse-width modulation)
261		RW
262
263pwm[1-*]_freq	Base PWM frequency in Hz.
264		Only possibly available when pwmN_mode is PWM, but not always
265		present even then.
266		RW
267
268pwm[1-*]_auto_channels_temp
269		Select which temperature channels affect this PWM output in
270		auto mode. Bitfield, 1 is temp1, 2 is temp2, 4 is temp3 etc...
271		Which values are possible depend on the chip used.
272		RW
273
274pwm[1-*]_auto_point[1-*]_pwm
275pwm[1-*]_auto_point[1-*]_temp
276pwm[1-*]_auto_point[1-*]_temp_hyst
277		Define the PWM vs temperature curve. Number of trip points is
278		chip-dependent. Use this for chips which associate trip points
279		to PWM output channels.
280		RW
281
282temp[1-*]_auto_point[1-*]_pwm
283temp[1-*]_auto_point[1-*]_temp
284temp[1-*]_auto_point[1-*]_temp_hyst
285		Define the PWM vs temperature curve. Number of trip points is
286		chip-dependent. Use this for chips which associate trip points
287		to temperature channels.
288		RW
289
290There is a third case where trip points are associated to both PWM output
291channels and temperature channels: the PWM values are associated to PWM
292output channels while the temperature values are associated to temperature
293channels. In that case, the result is determined by the mapping between
294temperature inputs and PWM outputs. When several temperature inputs are
295mapped to a given PWM output, this leads to several candidate PWM values.
296The actual result is up to the chip, but in general the highest candidate
297value (fastest fan speed) wins.
298
299
300****************
301* Temperatures *
302****************
303
304temp[1-*]_type	Sensor type selection.
305		Integers 1 to 6
306		RW
307		1: CPU embedded diode
308		2: 3904 transistor
309		3: thermal diode
310		4: thermistor
311		5: AMD AMDSI
312		6: Intel PECI
313		Not all types are supported by all chips
314
315temp[1-*]_max	Temperature max value.
316		Unit: millidegree Celsius (or millivolt, see below)
317		RW
318
319temp[1-*]_min	Temperature min value.
320		Unit: millidegree Celsius
321		RW
322
323temp[1-*]_max_hyst
324		Temperature hysteresis value for max limit.
325		Unit: millidegree Celsius
326		Must be reported as an absolute temperature, NOT a delta
327		from the max value.
328		RW
329
330temp[1-*]_min_hyst
331		Temperature hysteresis value for min limit.
332		Unit: millidegree Celsius
333		Must be reported as an absolute temperature, NOT a delta
334		from the min value.
335		RW
336
337temp[1-*]_input Temperature input value.
338		Unit: millidegree Celsius
339		RO
340
341temp[1-*]_crit	Temperature critical max value, typically greater than
342		corresponding temp_max values.
343		Unit: millidegree Celsius
344		RW
345
346temp[1-*]_crit_hyst
347		Temperature hysteresis value for critical limit.
348		Unit: millidegree Celsius
349		Must be reported as an absolute temperature, NOT a delta
350		from the critical value.
351		RW
352
353temp[1-*]_emergency
354		Temperature emergency max value, for chips supporting more than
355		two upper temperature limits. Must be equal or greater than
356		corresponding temp_crit values.
357		Unit: millidegree Celsius
358		RW
359
360temp[1-*]_emergency_hyst
361		Temperature hysteresis value for emergency limit.
362		Unit: millidegree Celsius
363		Must be reported as an absolute temperature, NOT a delta
364		from the emergency value.
365		RW
366
367temp[1-*]_lcrit	Temperature critical min value, typically lower than
368		corresponding temp_min values.
369		Unit: millidegree Celsius
370		RW
371
372temp[1-*]_lcrit_hyst
373		Temperature hysteresis value for critical min limit.
374		Unit: millidegree Celsius
375		Must be reported as an absolute temperature, NOT a delta
376		from the critical min value.
377		RW
378
379temp[1-*]_offset
380		Temperature offset which is added to the temperature reading
381		by the chip.
382		Unit: millidegree Celsius
383		Read/Write value.
384
385temp[1-*]_label	Suggested temperature channel label.
386		Text string
387		Should only be created if the driver has hints about what
388		this temperature channel is being used for, and user-space
389		doesn't. In all other cases, the label is provided by
390		user-space.
391		RO
392
393temp[1-*]_lowest
394		Historical minimum temperature
395		Unit: millidegree Celsius
396		RO
397
398temp[1-*]_highest
399		Historical maximum temperature
400		Unit: millidegree Celsius
401		RO
402
403temp[1-*]_reset_history
404		Reset temp_lowest and temp_highest
405		WO
406
407temp_reset_history
408		Reset temp_lowest and temp_highest for all sensors
409		WO
410
411Some chips measure temperature using external thermistors and an ADC, and
412report the temperature measurement as a voltage. Converting this voltage
413back to a temperature (or the other way around for limits) requires
414mathematical functions not available in the kernel, so the conversion
415must occur in user space. For these chips, all temp* files described
416above should contain values expressed in millivolt instead of millidegree
417Celsius. In other words, such temperature channels are handled as voltage
418channels by the driver.
419
420Also see the Alarms section for status flags associated with temperatures.
421
422
423************
424* Currents *
425************
426
427curr[1-*]_max	Current max value
428		Unit: milliampere
429		RW
430
431curr[1-*]_min	Current min value.
432		Unit: milliampere
433		RW
434
435curr[1-*]_lcrit	Current critical low value
436		Unit: milliampere
437		RW
438
439curr[1-*]_crit	Current critical high value.
440		Unit: milliampere
441		RW
442
443curr[1-*]_input	Current input value
444		Unit: milliampere
445		RO
446
447curr[1-*]_average
448		Average current use
449		Unit: milliampere
450		RO
451
452curr[1-*]_lowest
453		Historical minimum current
454		Unit: milliampere
455		RO
456
457curr[1-*]_highest
458		Historical maximum current
459		Unit: milliampere
460		RO
461
462curr[1-*]_reset_history
463		Reset currX_lowest and currX_highest
464		WO
465
466curr_reset_history
467		Reset currX_lowest and currX_highest for all sensors
468		WO
469
470Also see the Alarms section for status flags associated with currents.
471
472*********
473* Power *
474*********
475
476power[1-*]_average		Average power use
477				Unit: microWatt
478				RO
479
480power[1-*]_average_interval	Power use averaging interval.  A poll
481				notification is sent to this file if the
482				hardware changes the averaging interval.
483				Unit: milliseconds
484				RW
485
486power[1-*]_average_interval_max	Maximum power use averaging interval
487				Unit: milliseconds
488				RO
489
490power[1-*]_average_interval_min	Minimum power use averaging interval
491				Unit: milliseconds
492				RO
493
494power[1-*]_average_highest	Historical average maximum power use
495				Unit: microWatt
496				RO
497
498power[1-*]_average_lowest	Historical average minimum power use
499				Unit: microWatt
500				RO
501
502power[1-*]_average_max		A poll notification is sent to
503				power[1-*]_average when power use
504				rises above this value.
505				Unit: microWatt
506				RW
507
508power[1-*]_average_min		A poll notification is sent to
509				power[1-*]_average when power use
510				sinks below this value.
511				Unit: microWatt
512				RW
513
514power[1-*]_input		Instantaneous power use
515				Unit: microWatt
516				RO
517
518power[1-*]_input_highest	Historical maximum power use
519				Unit: microWatt
520				RO
521
522power[1-*]_input_lowest		Historical minimum power use
523				Unit: microWatt
524				RO
525
526power[1-*]_reset_history	Reset input_highest, input_lowest,
527				average_highest and average_lowest.
528				WO
529
530power[1-*]_accuracy		Accuracy of the power meter.
531				Unit: Percent
532				RO
533
534power[1-*]_cap			If power use rises above this limit, the
535				system should take action to reduce power use.
536				A poll notification is sent to this file if the
537				cap is changed by the hardware.  The *_cap
538				files only appear if the cap is known to be
539				enforced by hardware.
540				Unit: microWatt
541				RW
542
543power[1-*]_cap_hyst		Margin of hysteresis built around capping and
544				notification.
545				Unit: microWatt
546				RW
547
548power[1-*]_cap_max		Maximum cap that can be set.
549				Unit: microWatt
550				RO
551
552power[1-*]_cap_min		Minimum cap that can be set.
553				Unit: microWatt
554				RO
555
556power[1-*]_max			Maximum power.
557				Unit: microWatt
558				RW
559
560power[1-*]_crit			Critical maximum power.
561				If power rises to or above this limit, the
562				system is expected take drastic action to reduce
563				power consumption, such as a system shutdown or
564				a forced powerdown of some devices.
565				Unit: microWatt
566				RW
567
568Also see the Alarms section for status flags associated with power readings.
569
570**********
571* Energy *
572**********
573
574energy[1-*]_input		Cumulative energy use
575				Unit: microJoule
576				RO
577
578
579************
580* Humidity *
581************
582
583humidity[1-*]_input		Humidity
584				Unit: milli-percent (per cent mille, pcm)
585				RO
586
587
588**********
589* Alarms *
590**********
591
592Each channel or limit may have an associated alarm file, containing a
593boolean value. 1 means than an alarm condition exists, 0 means no alarm.
594
595Usually a given chip will either use channel-related alarms, or
596limit-related alarms, not both. The driver should just reflect the hardware
597implementation.
598
599in[0-*]_alarm
600curr[1-*]_alarm
601power[1-*]_alarm
602fan[1-*]_alarm
603temp[1-*]_alarm
604		Channel alarm
605		0: no alarm
606		1: alarm
607		RO
608
609OR
610
611in[0-*]_min_alarm
612in[0-*]_max_alarm
613in[0-*]_lcrit_alarm
614in[0-*]_crit_alarm
615curr[1-*]_min_alarm
616curr[1-*]_max_alarm
617curr[1-*]_lcrit_alarm
618curr[1-*]_crit_alarm
619power[1-*]_cap_alarm
620power[1-*]_max_alarm
621power[1-*]_crit_alarm
622fan[1-*]_min_alarm
623fan[1-*]_max_alarm
624temp[1-*]_min_alarm
625temp[1-*]_max_alarm
626temp[1-*]_lcrit_alarm
627temp[1-*]_crit_alarm
628temp[1-*]_emergency_alarm
629		Limit alarm
630		0: no alarm
631		1: alarm
632		RO
633
634Each input channel may have an associated fault file. This can be used
635to notify open diodes, unconnected fans etc. where the hardware
636supports it. When this boolean has value 1, the measurement for that
637channel should not be trusted.
638
639fan[1-*]_fault
640temp[1-*]_fault
641		Input fault condition
642		0: no fault occurred
643		1: fault condition
644		RO
645
646Some chips also offer the possibility to get beeped when an alarm occurs:
647
648beep_enable	Master beep enable
649		0: no beeps
650		1: beeps
651		RW
652
653in[0-*]_beep
654curr[1-*]_beep
655fan[1-*]_beep
656temp[1-*]_beep
657		Channel beep
658		0: disable
659		1: enable
660		RW
661
662In theory, a chip could provide per-limit beep masking, but no such chip
663was seen so far.
664
665Old drivers provided a different, non-standard interface to alarms and
666beeps. These interface files are deprecated, but will be kept around
667for compatibility reasons:
668
669alarms		Alarm bitmask.
670		RO
671		Integer representation of one to four bytes.
672		A '1' bit means an alarm.
673		Chips should be programmed for 'comparator' mode so that
674		the alarm will 'come back' after you read the register
675		if it is still valid.
676		Generally a direct representation of a chip's internal
677		alarm registers; there is no standard for the position
678		of individual bits. For this reason, the use of this
679		interface file for new drivers is discouraged. Use
680		individual *_alarm and *_fault files instead.
681		Bits are defined in kernel/include/sensors.h.
682
683beep_mask	Bitmask for beep.
684		Same format as 'alarms' with the same bit locations,
685		use discouraged for the same reason. Use individual
686		*_beep files instead.
687		RW
688
689
690***********************
691* Intrusion detection *
692***********************
693
694intrusion[0-*]_alarm
695		Chassis intrusion detection
696		0: OK
697		1: intrusion detected
698		RW
699		Contrary to regular alarm flags which clear themselves
700		automatically when read, this one sticks until cleared by
701		the user. This is done by writing 0 to the file. Writing
702		other values is unsupported.
703
704intrusion[0-*]_beep
705		Chassis intrusion beep
706		0: disable
707		1: enable
708		RW
709
710
711sysfs attribute writes interpretation
712-------------------------------------
713
714hwmon sysfs attributes always contain numbers, so the first thing to do is to
715convert the input to a number, there are 2 ways todo this depending whether
716the number can be negative or not:
717unsigned long u = simple_strtoul(buf, NULL, 10);
718long s = simple_strtol(buf, NULL, 10);
719
720With buf being the buffer with the user input being passed by the kernel.
721Notice that we do not use the second argument of strto[u]l, and thus cannot
722tell when 0 is returned, if this was really 0 or is caused by invalid input.
723This is done deliberately as checking this everywhere would add a lot of
724code to the kernel.
725
726Notice that it is important to always store the converted value in an
727unsigned long or long, so that no wrap around can happen before any further
728checking.
729
730After the input string is converted to an (unsigned) long, the value should be
731checked if its acceptable. Be careful with further conversions on the value
732before checking it for validity, as these conversions could still cause a wrap
733around before the check. For example do not multiply the result, and only
734add/subtract if it has been divided before the add/subtract.
735
736What to do if a value is found to be invalid, depends on the type of the
737sysfs attribute that is being set. If it is a continuous setting like a
738tempX_max or inX_max attribute, then the value should be clamped to its
739limits using clamp_val(value, min_limit, max_limit). If it is not continuous
740like for example a tempX_type, then when an invalid value is written,
741-EINVAL should be returned.
742
743Example1, temp1_max, register is a signed 8 bit value (-128 - 127 degrees):
744
745	long v = simple_strtol(buf, NULL, 10) / 1000;
746	v = clamp_val(v, -128, 127);
747	/* write v to register */
748
749Example2, fan divider setting, valid values 2, 4 and 8:
750
751	unsigned long v = simple_strtoul(buf, NULL, 10);
752
753	switch (v) {
754	case 2: v = 1; break;
755	case 4: v = 2; break;
756	case 8: v = 3; break;
757	default:
758		return -EINVAL;
759	}
760	/* write v to register */
761