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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-*]_label Suggested voltage channel label.
143 Text string
144 Should only be created if the driver has hints about what
145 this voltage channel is being used for, and user-space
146 doesn't. In all other cases, the label is provided by
147 user-space.
148 RO
150 cpu[0-*]_vid CPU core reference voltage.
151 Unit: millivolt
152 RO
153 Not always correct.
155 vrm Voltage Regulator Module version number.
156 RW (but changing it should no more be necessary)
157 Originally the VRM standard version multiplied by 10, but now
158 an arbitrary number, as not all standards have a version
159 number.
160 Affects the way the driver calculates the CPU core reference
161 voltage from the vid pins.
163 Also see the Alarms section for status flags associated with voltages.
166 ********
167 * Fans *
168 ********
170 fan[1-*]_min Fan minimum value
171 Unit: revolution/min (RPM)
172 RW
174 fan[1-*]_max Fan maximum value
175 Unit: revolution/min (RPM)
176 Only rarely supported by the hardware.
177 RW
179 fan[1-*]_input Fan input value.
180 Unit: revolution/min (RPM)
181 RO
183 fan[1-*]_div Fan divisor.
184 Integer value in powers of two (1, 2, 4, 8, 16, 32, 64, 128).
185 RW
186 Some chips only support values 1, 2, 4 and 8.
187 Note that this is actually an internal clock divisor, which
188 affects the measurable speed range, not the read value.
190 fan[1-*]_pulses Number of tachometer pulses per fan revolution.
191 Integer value, typically between 1 and 4.
192 RW
193 This value is a characteristic of the fan connected to the
194 device's input, so it has to be set in accordance with the fan
195 model.
196 Should only be created if the chip has a register to configure
197 the number of pulses. In the absence of such a register (and
198 thus attribute) the value assumed by all devices is 2 pulses
199 per fan revolution.
201 fan[1-*]_target
202 Desired fan speed
203 Unit: revolution/min (RPM)
204 RW
205 Only makes sense if the chip supports closed-loop fan speed
206 control based on the measured fan speed.
208 fan[1-*]_label Suggested fan channel label.
209 Text string
210 Should only be created if the driver has hints about what
211 this fan channel is being used for, and user-space doesn't.
212 In all other cases, the label is provided by user-space.
213 RO
215 Also see the Alarms section for status flags associated with fans.
218 *******
219 * PWM *
220 *******
222 pwm[1-*] Pulse width modulation fan control.
223 Integer value in the range 0 to 255
224 RW
225 255 is max or 100%.
227 pwm[1-*]_enable
228 Fan speed control method:
229 0: no fan speed control (i.e. fan at full speed)
230 1: manual fan speed control enabled (using pwm[1-*])
231 2+: automatic fan speed control enabled
232 Check individual chip documentation files for automatic mode
233 details.
234 RW
236 pwm[1-*]_mode 0: DC mode (direct current)
237 1: PWM mode (pulse-width modulation)
238 RW
240 pwm[1-*]_freq Base PWM frequency in Hz.
241 Only possibly available when pwmN_mode is PWM, but not always
242 present even then.
243 RW
245 pwm[1-*]_auto_channels_temp
246 Select which temperature channels affect this PWM output in
247 auto mode. Bitfield, 1 is temp1, 2 is temp2, 4 is temp3 etc...
248 Which values are possible depend on the chip used.
249 RW
251 pwm[1-*]_auto_point[1-*]_pwm
252 pwm[1-*]_auto_point[1-*]_temp
253 pwm[1-*]_auto_point[1-*]_temp_hyst
254 Define the PWM vs temperature curve. Number of trip points is
255 chip-dependent. Use this for chips which associate trip points
256 to PWM output channels.
257 RW
259 temp[1-*]_auto_point[1-*]_pwm
260 temp[1-*]_auto_point[1-*]_temp
261 temp[1-*]_auto_point[1-*]_temp_hyst
262 Define the PWM vs temperature curve. Number of trip points is
263 chip-dependent. Use this for chips which associate trip points
264 to temperature channels.
265 RW
267 There is a third case where trip points are associated to both PWM output
268 channels and temperature channels: the PWM values are associated to PWM
269 output channels while the temperature values are associated to temperature
270 channels. In that case, the result is determined by the mapping between
271 temperature inputs and PWM outputs. When several temperature inputs are
272 mapped to a given PWM output, this leads to several candidate PWM values.
273 The actual result is up to the chip, but in general the highest candidate
274 value (fastest fan speed) wins.
277 ****************
278 * Temperatures *
279 ****************
281 temp[1-*]_type Sensor type selection.
282 Integers 1 to 6
283 RW
284 1: PII/Celeron Diode
285 2: 3904 transistor
286 3: thermal diode
287 4: thermistor
288 5: AMD AMDSI
289 6: Intel PECI
290 Not all types are supported by all chips
292 temp[1-*]_max Temperature max value.
293 Unit: millidegree Celsius (or millivolt, see below)
294 RW
296 temp[1-*]_min Temperature min value.
297 Unit: millidegree Celsius
298 RW
300 temp[1-*]_max_hyst
301 Temperature hysteresis value for max limit.
302 Unit: millidegree Celsius
303 Must be reported as an absolute temperature, NOT a delta
304 from the max value.
305 RW
307 temp[1-*]_input Temperature input value.
308 Unit: millidegree Celsius
309 RO
311 temp[1-*]_crit Temperature critical max value, typically greater than
312 corresponding temp_max values.
313 Unit: millidegree Celsius
314 RW
316 temp[1-*]_crit_hyst
317 Temperature hysteresis value for critical limit.
318 Unit: millidegree Celsius
319 Must be reported as an absolute temperature, NOT a delta
320 from the critical value.
321 RW
323 temp[1-*]_emergency
324 Temperature emergency max value, for chips supporting more than
325 two upper temperature limits. Must be equal or greater than
326 corresponding temp_crit values.
327 Unit: millidegree Celsius
328 RW
330 temp[1-*]_emergency_hyst
331 Temperature hysteresis value for emergency limit.
332 Unit: millidegree Celsius
333 Must be reported as an absolute temperature, NOT a delta
334 from the emergency value.
335 RW
337 temp[1-*]_lcrit Temperature critical min value, typically lower than
338 corresponding temp_min values.
339 Unit: millidegree Celsius
340 RW
342 temp[1-*]_offset
343 Temperature offset which is added to the temperature reading
344 by the chip.
345 Unit: millidegree Celsius
346 Read/Write value.
348 temp[1-*]_label Suggested temperature channel label.
349 Text string
350 Should only be created if the driver has hints about what
351 this temperature channel is being used for, and user-space
352 doesn't. In all other cases, the label is provided by
353 user-space.
354 RO
356 temp[1-*]_lowest
357 Historical minimum temperature
358 Unit: millidegree Celsius
359 RO
361 temp[1-*]_highest
362 Historical maximum temperature
363 Unit: millidegree Celsius
364 RO
366 temp[1-*]_reset_history
367 Reset temp_lowest and temp_highest
368 WO
370 temp_reset_history
371 Reset temp_lowest and temp_highest for all sensors
372 WO
374 Some chips measure temperature using external thermistors and an ADC, and
375 report the temperature measurement as a voltage. Converting this voltage
376 back to a temperature (or the other way around for limits) requires
377 mathematical functions not available in the kernel, so the conversion
378 must occur in user space. For these chips, all temp* files described
379 above should contain values expressed in millivolt instead of millidegree
380 Celsius. In other words, such temperature channels are handled as voltage
381 channels by the driver.
383 Also see the Alarms section for status flags associated with temperatures.
386 ************
387 * Currents *
388 ************
390 curr[1-*]_max Current max value
391 Unit: milliampere
392 RW
394 curr[1-*]_min Current min value.
395 Unit: milliampere
396 RW
398 curr[1-*]_lcrit Current critical low value
399 Unit: milliampere
400 RW
402 curr[1-*]_crit Current critical high value.
403 Unit: milliampere
404 RW
406 curr[1-*]_input Current input value
407 Unit: milliampere
408 RO
410 Also see the Alarms section for status flags associated with currents.
412 *********
413 * Power *
414 *********
416 power[1-*]_average Average power use
417 Unit: microWatt
418 RO
420 power[1-*]_average_interval Power use averaging interval. A poll
421 notification is sent to this file if the
422 hardware changes the averaging interval.
423 Unit: milliseconds
424 RW
426 power[1-*]_average_interval_max Maximum power use averaging interval
427 Unit: milliseconds
428 RO
430 power[1-*]_average_interval_min Minimum power use averaging interval
431 Unit: milliseconds
432 RO
434 power[1-*]_average_highest Historical average maximum power use
435 Unit: microWatt
436 RO
438 power[1-*]_average_lowest Historical average minimum power use
439 Unit: microWatt
440 RO
442 power[1-*]_average_max A poll notification is sent to
443 power[1-*]_average when power use
444 rises above this value.
445 Unit: microWatt
446 RW
448 power[1-*]_average_min A poll notification is sent to
449 power[1-*]_average when power use
450 sinks below this value.
451 Unit: microWatt
452 RW
454 power[1-*]_input Instantaneous power use
455 Unit: microWatt
456 RO
458 power[1-*]_input_highest Historical maximum power use
459 Unit: microWatt
460 RO
462 power[1-*]_input_lowest Historical minimum power use
463 Unit: microWatt
464 RO
466 power[1-*]_reset_history Reset input_highest, input_lowest,
467 average_highest and average_lowest.
468 WO
470 power[1-*]_accuracy Accuracy of the power meter.
471 Unit: Percent
472 RO
474 power[1-*]_cap If power use rises above this limit, the
475 system should take action to reduce power use.
476 A poll notification is sent to this file if the
477 cap is changed by the hardware. The *_cap
478 files only appear if the cap is known to be
479 enforced by hardware.
480 Unit: microWatt
481 RW
483 power[1-*]_cap_hyst Margin of hysteresis built around capping and
484 notification.
485 Unit: microWatt
486 RW
488 power[1-*]_cap_max Maximum cap that can be set.
489 Unit: microWatt
490 RO
492 power[1-*]_cap_min Minimum cap that can be set.
493 Unit: microWatt
494 RO
496 power[1-*]_max Maximum power.
497 Unit: microWatt
498 RW
500 power[1-*]_crit Critical maximum power.
501 If power rises to or above this limit, the
502 system is expected take drastic action to reduce
503 power consumption, such as a system shutdown or
504 a forced powerdown of some devices.
505 Unit: microWatt
506 RW
508 Also see the Alarms section for status flags associated with power readings.
510 **********
511 * Energy *
512 **********
514 energy[1-*]_input Cumulative energy use
515 Unit: microJoule
516 RO
519 ************
520 * Humidity *
521 ************
523 humidity[1-*]_input Humidity
524 Unit: milli-percent (per cent mille, pcm)
525 RO
528 **********
529 * Alarms *
530 **********
532 Each channel or limit may have an associated alarm file, containing a
533 boolean value. 1 means than an alarm condition exists, 0 means no alarm.
535 Usually a given chip will either use channel-related alarms, or
536 limit-related alarms, not both. The driver should just reflect the hardware
537 implementation.
539 in[0-*]_alarm
540 curr[1-*]_alarm
541 power[1-*]_alarm
542 fan[1-*]_alarm
543 temp[1-*]_alarm
544 Channel alarm
545 0: no alarm
546 1: alarm
547 RO
549 OR
551 in[0-*]_min_alarm
552 in[0-*]_max_alarm
553 in[0-*]_lcrit_alarm
554 in[0-*]_crit_alarm
555 curr[1-*]_min_alarm
556 curr[1-*]_max_alarm
557 curr[1-*]_lcrit_alarm
558 curr[1-*]_crit_alarm
559 power[1-*]_cap_alarm
560 power[1-*]_max_alarm
561 power[1-*]_crit_alarm
562 fan[1-*]_min_alarm
563 fan[1-*]_max_alarm
564 temp[1-*]_min_alarm
565 temp[1-*]_max_alarm
566 temp[1-*]_lcrit_alarm
567 temp[1-*]_crit_alarm
568 temp[1-*]_emergency_alarm
569 Limit alarm
570 0: no alarm
571 1: alarm
572 RO
574 Each input channel may have an associated fault file. This can be used
575 to notify open diodes, unconnected fans etc. where the hardware
576 supports it. When this boolean has value 1, the measurement for that
577 channel should not be trusted.
579 fan[1-*]_fault
580 temp[1-*]_fault
581 Input fault condition
582 0: no fault occurred
583 1: fault condition
584 RO
586 Some chips also offer the possibility to get beeped when an alarm occurs:
588 beep_enable Master beep enable
589 0: no beeps
590 1: beeps
591 RW
593 in[0-*]_beep
594 curr[1-*]_beep
595 fan[1-*]_beep
596 temp[1-*]_beep
597 Channel beep
598 0: disable
599 1: enable
600 RW
602 In theory, a chip could provide per-limit beep masking, but no such chip
603 was seen so far.
605 Old drivers provided a different, non-standard interface to alarms and
606 beeps. These interface files are deprecated, but will be kept around
607 for compatibility reasons:
609 alarms Alarm bitmask.
610 RO
611 Integer representation of one to four bytes.
612 A '1' bit means an alarm.
613 Chips should be programmed for 'comparator' mode so that
614 the alarm will 'come back' after you read the register
615 if it is still valid.
616 Generally a direct representation of a chip's internal
617 alarm registers; there is no standard for the position
618 of individual bits. For this reason, the use of this
619 interface file for new drivers is discouraged. Use
620 individual *_alarm and *_fault files instead.
621 Bits are defined in kernel/include/sensors.h.
623 beep_mask Bitmask for beep.
624 Same format as 'alarms' with the same bit locations,
625 use discouraged for the same reason. Use individual
626 *_beep files instead.
627 RW
630 ***********************
631 * Intrusion detection *
632 ***********************
634 intrusion[0-*]_alarm
635 Chassis intrusion detection
636 0: OK
637 1: intrusion detected
638 RW
639 Contrary to regular alarm flags which clear themselves
640 automatically when read, this one sticks until cleared by
641 the user. This is done by writing 0 to the file. Writing
642 other values is unsupported.
644 intrusion[0-*]_beep
645 Chassis intrusion beep
646 0: disable
647 1: enable
648 RW
651 sysfs attribute writes interpretation
652 -------------------------------------
654 hwmon sysfs attributes always contain numbers, so the first thing to do is to
655 convert the input to a number, there are 2 ways todo this depending whether
656 the number can be negative or not:
657 unsigned long u = simple_strtoul(buf, NULL, 10);
658 long s = simple_strtol(buf, NULL, 10);
660 With buf being the buffer with the user input being passed by the kernel.
661 Notice that we do not use the second argument of strto[u]l, and thus cannot
662 tell when 0 is returned, if this was really 0 or is caused by invalid input.
663 This is done deliberately as checking this everywhere would add a lot of
664 code to the kernel.
666 Notice that it is important to always store the converted value in an
667 unsigned long or long, so that no wrap around can happen before any further
668 checking.
670 After the input string is converted to an (unsigned) long, the value should be
671 checked if its acceptable. Be careful with further conversions on the value
672 before checking it for validity, as these conversions could still cause a wrap
673 around before the check. For example do not multiply the result, and only
674 add/subtract if it has been divided before the add/subtract.
676 What to do if a value is found to be invalid, depends on the type of the
677 sysfs attribute that is being set. If it is a continuous setting like a
678 tempX_max or inX_max attribute, then the value should be clamped to its
679 limits using SENSORS_LIMIT(value, min_limit, max_limit). If it is not
680 continuous like for example a tempX_type, then when an invalid value is
681 written, -EINVAL should be returned.
683 Example1, temp1_max, register is a signed 8 bit value (-128 - 127 degrees):
685 long v = simple_strtol(buf, NULL, 10) / 1000;
686 v = SENSORS_LIMIT(v, -128, 127);
687 /* write v to register */
689 Example2, fan divider setting, valid values 2, 4 and 8:
691 unsigned long v = simple_strtoul(buf, NULL, 10);
693 switch (v) {
694 case 2: v = 1; break;
695 case 4: v = 2; break;
696 case 8: v = 3; break;
697 default:
698 return -EINVAL;
699 }
700 /* write v to register */