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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 spaces nor dashes, representing the chip name. This is
90 the only mandatory attribute.
91 I2C devices get this attribute created automatically.
92 RO
94 update_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.
101 ************
102 * Voltages *
103 ************
105 in[0-*]_min Voltage min value.
106 Unit: millivolt
107 RW
109 in[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.
116 in[0-*]_max Voltage max value.
117 Unit: millivolt
118 RW
120 in[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.
127 in[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.
142 in[0-*]_average
143 Average voltage
144 Unit: millivolt
145 RO
147 in[0-*]_lowest
148 Historical minimum voltage
149 Unit: millivolt
150 RO
152 in[0-*]_highest
153 Historical maximum voltage
154 Unit: millivolt
155 RO
157 in[0-*]_reset_history
158 Reset inX_lowest and inX_highest
159 WO
161 in_reset_history
162 Reset inX_lowest and inX_highest for all sensors
163 WO
165 in[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
173 cpu[0-*]_vid CPU core reference voltage.
174 Unit: millivolt
175 RO
176 Not always correct.
178 vrm 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.
186 Also see the Alarms section for status flags associated with voltages.
189 ********
190 * Fans *
191 ********
193 fan[1-*]_min Fan minimum value
194 Unit: revolution/min (RPM)
195 RW
197 fan[1-*]_max Fan maximum value
198 Unit: revolution/min (RPM)
199 Only rarely supported by the hardware.
200 RW
202 fan[1-*]_input Fan input value.
203 Unit: revolution/min (RPM)
204 RO
206 fan[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.
213 fan[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.
224 fan[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.
231 fan[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
238 Also see the Alarms section for status flags associated with fans.
241 *******
242 * PWM *
243 *******
245 pwm[1-*] Pulse width modulation fan control.
246 Integer value in the range 0 to 255
247 RW
248 255 is max or 100%.
250 pwm[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
259 pwm[1-*]_mode 0: DC mode (direct current)
260 1: PWM mode (pulse-width modulation)
261 RW
263 pwm[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
268 pwm[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
274 pwm[1-*]_auto_point[1-*]_pwm
275 pwm[1-*]_auto_point[1-*]_temp
276 pwm[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
282 temp[1-*]_auto_point[1-*]_pwm
283 temp[1-*]_auto_point[1-*]_temp
284 temp[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
290 There is a third case where trip points are associated to both PWM output
291 channels and temperature channels: the PWM values are associated to PWM
292 output channels while the temperature values are associated to temperature
293 channels. In that case, the result is determined by the mapping between
294 temperature inputs and PWM outputs. When several temperature inputs are
295 mapped to a given PWM output, this leads to several candidate PWM values.
296 The actual result is up to the chip, but in general the highest candidate
297 value (fastest fan speed) wins.
300 ****************
301 * Temperatures *
302 ****************
304 temp[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
315 temp[1-*]_max Temperature max value.
316 Unit: millidegree Celsius (or millivolt, see below)
317 RW
319 temp[1-*]_min Temperature min value.
320 Unit: millidegree Celsius
321 RW
323 temp[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
330 temp[1-*]_input Temperature input value.
331 Unit: millidegree Celsius
332 RO
334 temp[1-*]_crit Temperature critical max value, typically greater than
335 corresponding temp_max values.
336 Unit: millidegree Celsius
337 RW
339 temp[1-*]_crit_hyst
340 Temperature hysteresis value for critical limit.
341 Unit: millidegree Celsius
342 Must be reported as an absolute temperature, NOT a delta
343 from the critical value.
344 RW
346 temp[1-*]_emergency
347 Temperature emergency max value, for chips supporting more than
348 two upper temperature limits. Must be equal or greater than
349 corresponding temp_crit values.
350 Unit: millidegree Celsius
351 RW
353 temp[1-*]_emergency_hyst
354 Temperature hysteresis value for emergency limit.
355 Unit: millidegree Celsius
356 Must be reported as an absolute temperature, NOT a delta
357 from the emergency value.
358 RW
360 temp[1-*]_lcrit Temperature critical min value, typically lower than
361 corresponding temp_min values.
362 Unit: millidegree Celsius
363 RW
365 temp[1-*]_offset
366 Temperature offset which is added to the temperature reading
367 by the chip.
368 Unit: millidegree Celsius
369 Read/Write value.
371 temp[1-*]_label Suggested temperature channel label.
372 Text string
373 Should only be created if the driver has hints about what
374 this temperature channel is being used for, and user-space
375 doesn't. In all other cases, the label is provided by
376 user-space.
377 RO
379 temp[1-*]_lowest
380 Historical minimum temperature
381 Unit: millidegree Celsius
382 RO
384 temp[1-*]_highest
385 Historical maximum temperature
386 Unit: millidegree Celsius
387 RO
389 temp[1-*]_reset_history
390 Reset temp_lowest and temp_highest
391 WO
393 temp_reset_history
394 Reset temp_lowest and temp_highest for all sensors
395 WO
397 Some chips measure temperature using external thermistors and an ADC, and
398 report the temperature measurement as a voltage. Converting this voltage
399 back to a temperature (or the other way around for limits) requires
400 mathematical functions not available in the kernel, so the conversion
401 must occur in user space. For these chips, all temp* files described
402 above should contain values expressed in millivolt instead of millidegree
403 Celsius. In other words, such temperature channels are handled as voltage
404 channels by the driver.
406 Also see the Alarms section for status flags associated with temperatures.
409 ************
410 * Currents *
411 ************
413 curr[1-*]_max Current max value
414 Unit: milliampere
415 RW
417 curr[1-*]_min Current min value.
418 Unit: milliampere
419 RW
421 curr[1-*]_lcrit Current critical low value
422 Unit: milliampere
423 RW
425 curr[1-*]_crit Current critical high value.
426 Unit: milliampere
427 RW
429 curr[1-*]_input Current input value
430 Unit: milliampere
431 RO
433 curr[1-*]_average
434 Average current use
435 Unit: milliampere
436 RO
438 curr[1-*]_lowest
439 Historical minimum current
440 Unit: milliampere
441 RO
443 curr[1-*]_highest
444 Historical maximum current
445 Unit: milliampere
446 RO
448 curr[1-*]_reset_history
449 Reset currX_lowest and currX_highest
450 WO
452 curr_reset_history
453 Reset currX_lowest and currX_highest for all sensors
454 WO
456 Also see the Alarms section for status flags associated with currents.
458 *********
459 * Power *
460 *********
462 power[1-*]_average Average power use
463 Unit: microWatt
464 RO
466 power[1-*]_average_interval Power use averaging interval. A poll
467 notification is sent to this file if the
468 hardware changes the averaging interval.
469 Unit: milliseconds
470 RW
472 power[1-*]_average_interval_max Maximum power use averaging interval
473 Unit: milliseconds
474 RO
476 power[1-*]_average_interval_min Minimum power use averaging interval
477 Unit: milliseconds
478 RO
480 power[1-*]_average_highest Historical average maximum power use
481 Unit: microWatt
482 RO
484 power[1-*]_average_lowest Historical average minimum power use
485 Unit: microWatt
486 RO
488 power[1-*]_average_max A poll notification is sent to
489 power[1-*]_average when power use
490 rises above this value.
491 Unit: microWatt
492 RW
494 power[1-*]_average_min A poll notification is sent to
495 power[1-*]_average when power use
496 sinks below this value.
497 Unit: microWatt
498 RW
500 power[1-*]_input Instantaneous power use
501 Unit: microWatt
502 RO
504 power[1-*]_input_highest Historical maximum power use
505 Unit: microWatt
506 RO
508 power[1-*]_input_lowest Historical minimum power use
509 Unit: microWatt
510 RO
512 power[1-*]_reset_history Reset input_highest, input_lowest,
513 average_highest and average_lowest.
514 WO
516 power[1-*]_accuracy Accuracy of the power meter.
517 Unit: Percent
518 RO
520 power[1-*]_cap If power use rises above this limit, the
521 system should take action to reduce power use.
522 A poll notification is sent to this file if the
523 cap is changed by the hardware. The *_cap
524 files only appear if the cap is known to be
525 enforced by hardware.
526 Unit: microWatt
527 RW
529 power[1-*]_cap_hyst Margin of hysteresis built around capping and
530 notification.
531 Unit: microWatt
532 RW
534 power[1-*]_cap_max Maximum cap that can be set.
535 Unit: microWatt
536 RO
538 power[1-*]_cap_min Minimum cap that can be set.
539 Unit: microWatt
540 RO
542 power[1-*]_max Maximum power.
543 Unit: microWatt
544 RW
546 power[1-*]_crit Critical maximum power.
547 If power rises to or above this limit, the
548 system is expected take drastic action to reduce
549 power consumption, such as a system shutdown or
550 a forced powerdown of some devices.
551 Unit: microWatt
552 RW
554 Also see the Alarms section for status flags associated with power readings.
556 **********
557 * Energy *
558 **********
560 energy[1-*]_input Cumulative energy use
561 Unit: microJoule
562 RO
565 ************
566 * Humidity *
567 ************
569 humidity[1-*]_input Humidity
570 Unit: milli-percent (per cent mille, pcm)
571 RO
574 **********
575 * Alarms *
576 **********
578 Each channel or limit may have an associated alarm file, containing a
579 boolean value. 1 means than an alarm condition exists, 0 means no alarm.
581 Usually a given chip will either use channel-related alarms, or
582 limit-related alarms, not both. The driver should just reflect the hardware
583 implementation.
585 in[0-*]_alarm
586 curr[1-*]_alarm
587 power[1-*]_alarm
588 fan[1-*]_alarm
589 temp[1-*]_alarm
590 Channel alarm
591 0: no alarm
592 1: alarm
593 RO
595 OR
597 in[0-*]_min_alarm
598 in[0-*]_max_alarm
599 in[0-*]_lcrit_alarm
600 in[0-*]_crit_alarm
601 curr[1-*]_min_alarm
602 curr[1-*]_max_alarm
603 curr[1-*]_lcrit_alarm
604 curr[1-*]_crit_alarm
605 power[1-*]_cap_alarm
606 power[1-*]_max_alarm
607 power[1-*]_crit_alarm
608 fan[1-*]_min_alarm
609 fan[1-*]_max_alarm
610 temp[1-*]_min_alarm
611 temp[1-*]_max_alarm
612 temp[1-*]_lcrit_alarm
613 temp[1-*]_crit_alarm
614 temp[1-*]_emergency_alarm
615 Limit alarm
616 0: no alarm
617 1: alarm
618 RO
620 Each input channel may have an associated fault file. This can be used
621 to notify open diodes, unconnected fans etc. where the hardware
622 supports it. When this boolean has value 1, the measurement for that
623 channel should not be trusted.
625 fan[1-*]_fault
626 temp[1-*]_fault
627 Input fault condition
628 0: no fault occurred
629 1: fault condition
630 RO
632 Some chips also offer the possibility to get beeped when an alarm occurs:
634 beep_enable Master beep enable
635 0: no beeps
636 1: beeps
637 RW
639 in[0-*]_beep
640 curr[1-*]_beep
641 fan[1-*]_beep
642 temp[1-*]_beep
643 Channel beep
644 0: disable
645 1: enable
646 RW
648 In theory, a chip could provide per-limit beep masking, but no such chip
649 was seen so far.
651 Old drivers provided a different, non-standard interface to alarms and
652 beeps. These interface files are deprecated, but will be kept around
653 for compatibility reasons:
655 alarms Alarm bitmask.
656 RO
657 Integer representation of one to four bytes.
658 A '1' bit means an alarm.
659 Chips should be programmed for 'comparator' mode so that
660 the alarm will 'come back' after you read the register
661 if it is still valid.
662 Generally a direct representation of a chip's internal
663 alarm registers; there is no standard for the position
664 of individual bits. For this reason, the use of this
665 interface file for new drivers is discouraged. Use
666 individual *_alarm and *_fault files instead.
667 Bits are defined in kernel/include/sensors.h.
669 beep_mask Bitmask for beep.
670 Same format as 'alarms' with the same bit locations,
671 use discouraged for the same reason. Use individual
672 *_beep files instead.
673 RW
676 ***********************
677 * Intrusion detection *
678 ***********************
680 intrusion[0-*]_alarm
681 Chassis intrusion detection
682 0: OK
683 1: intrusion detected
684 RW
685 Contrary to regular alarm flags which clear themselves
686 automatically when read, this one sticks until cleared by
687 the user. This is done by writing 0 to the file. Writing
688 other values is unsupported.
690 intrusion[0-*]_beep
691 Chassis intrusion beep
692 0: disable
693 1: enable
694 RW
697 sysfs attribute writes interpretation
698 -------------------------------------
700 hwmon sysfs attributes always contain numbers, so the first thing to do is to
701 convert the input to a number, there are 2 ways todo this depending whether
702 the number can be negative or not:
703 unsigned long u = simple_strtoul(buf, NULL, 10);
704 long s = simple_strtol(buf, NULL, 10);
706 With buf being the buffer with the user input being passed by the kernel.
707 Notice that we do not use the second argument of strto[u]l, and thus cannot
708 tell when 0 is returned, if this was really 0 or is caused by invalid input.
709 This is done deliberately as checking this everywhere would add a lot of
710 code to the kernel.
712 Notice that it is important to always store the converted value in an
713 unsigned long or long, so that no wrap around can happen before any further
714 checking.
716 After the input string is converted to an (unsigned) long, the value should be
717 checked if its acceptable. Be careful with further conversions on the value
718 before checking it for validity, as these conversions could still cause a wrap
719 around before the check. For example do not multiply the result, and only
720 add/subtract if it has been divided before the add/subtract.
722 What to do if a value is found to be invalid, depends on the type of the
723 sysfs attribute that is being set. If it is a continuous setting like a
724 tempX_max or inX_max attribute, then the value should be clamped to its
725 limits using SENSORS_LIMIT(value, min_limit, max_limit). If it is not
726 continuous like for example a tempX_type, then when an invalid value is
727 written, -EINVAL should be returned.
729 Example1, temp1_max, register is a signed 8 bit value (-128 - 127 degrees):
731 long v = simple_strtol(buf, NULL, 10) / 1000;
732 v = SENSORS_LIMIT(v, -128, 127);
733 /* write v to register */
735 Example2, fan divider setting, valid values 2, 4 and 8:
737 unsigned long v = simple_strtoul(buf, NULL, 10);
739 switch (v) {
740 case 2: v = 1; break;
741 case 4: v = 2; break;
742 case 8: v = 3; break;
743 default:
744 return -EINVAL;
745 }
746 /* write v to register */