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