1 Naming and data format standards for sysfs files
2 ================================================
3
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.
11
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.
21
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.
25
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.
32
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*`.
36
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.
43
44 All sysfs values are fixed point numbers.
45
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.
56
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.
62
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.
67
68 Attribute access
69 ----------------
70
71 Hardware monitoring sysfs attributes are displayed by unrestricted userspace
72 applications. For this reason, all standard ABI attributes shall be world
73 readable. Writeable standard ABI attributes shall be writeable only for
74 privileged users.
75
76 -------------------------------------------------------------------------
77
78 ======= ===========================================
79 `[0-*]` denotes any positive number starting from 0
80 `[1-*]` denotes any positive number starting from 1
81 RO read only value
82 WO write only value
83 RW read/write value
84 ======= ===========================================
85
86 Read/write values may be read-only for some chips, depending on the
87 hardware implementation.
88
89 All entries (except name) are optional, and should only be created in a
90 given driver if the chip has the feature.
91
92 See Documentation/ABI/testing/sysfs-class-hwmon for a complete description
93 of the attributes.
94
95 *****************
96 Global attributes
97 *****************
98
99 `name`
100 The chip name.
101
102 `label`
103 A descriptive label that allows to uniquely identify a device
104 within the system.
105
106 `update_interval`
107 The interval at which the chip will update readings.
108
109
110 ********
111 Voltages
112 ********
113
114 `in[0-*]_min`
115 Voltage min value.
116
117 `in[0-*]_lcrit`
118 Voltage critical min value.
119
120 `in[0-*]_max`
121 Voltage max value.
122
123 `in[0-*]_crit`
124 Voltage critical max value.
125
126 `in[0-*]_input`
127 Voltage input value.
128
129 `in[0-*]_average`
130 Average voltage
131
132 `in[0-*]_lowest`
133 Historical minimum voltage
134
135 `in[0-*]_highest`
136 Historical maximum voltage
137
138 `in[0-*]_reset_history`
139 Reset inX_lowest and inX_highest
140
141 `in_reset_history`
142 Reset inX_lowest and inX_highest for all sensors
143
144 `in[0-*]_label`
145 Suggested voltage channel label.
146
147 `in[0-*]_enable`
148 Enable or disable the sensors.
149
150 `cpu[0-*]_vid`
151 CPU core reference voltage.
152
153 `vrm`
154 Voltage Regulator Module version number.
155
156 `in[0-*]_rated_min`
157 Minimum rated voltage.
158
159 `in[0-*]_rated_max`
160 Maximum rated voltage.
161
162 Also see the Alarms section for status flags associated with voltages.
163
164
165 ****
166 Fans
167 ****
168
169 `fan[1-*]_min`
170 Fan minimum value
171
172 `fan[1-*]_max`
173 Fan maximum value
174
175 `fan[1-*]_input`
176 Fan input value.
177
178 `fan[1-*]_div`
179 Fan divisor.
180
181 `fan[1-*]_pulses`
182 Number of tachometer pulses per fan revolution.
183
184 `fan[1-*]_target`
185 Desired fan speed
186
187 `fan[1-*]_label`
188 Suggested fan channel label.
189
190 `fan[1-*]_enable`
191 Enable or disable the sensors.
192
193 Also see the Alarms section for status flags associated with fans.
194
195
196 ***
197 PWM
198 ***
199
200 `pwm[1-*]`
201 Pulse width modulation fan control.
202
203 `pwm[1-*]_enable`
204 Fan speed control method.
205
206 `pwm[1-*]_mode`
207 direct current or pulse-width modulation.
208
209 `pwm[1-*]_freq`
210 Base PWM frequency in Hz.
211
212 `pwm[1-*]_auto_channels_temp`
213 Select which temperature channels affect this PWM output in
214 auto mode.
215
216 `pwm[1-*]_auto_point[1-*]_pwm` / `pwm[1-*]_auto_point[1-*]_temp` / `pwm[1-*]_auto_point[1-*]_temp_hyst`
217 Define the PWM vs temperature curve.
218
219 `temp[1-*]_auto_point[1-*]_pwm` / `temp[1-*]_auto_point[1-*]_temp` / `temp[1-*]_auto_point[1-*]_temp_hyst`
220 Define the PWM vs temperature curve.
221
222 There is a third case where trip points are associated to both PWM output
223 channels and temperature channels: the PWM values are associated to PWM
224 output channels while the temperature values are associated to temperature
225 channels. In that case, the result is determined by the mapping between
226 temperature inputs and PWM outputs. When several temperature inputs are
227 mapped to a given PWM output, this leads to several candidate PWM values.
228 The actual result is up to the chip, but in general the highest candidate
229 value (fastest fan speed) wins.
230
231
232 ************
233 Temperatures
234 ************
235
236 `temp[1-*]_type`
237 Sensor type selection.
238
239 `temp[1-*]_max`
240 Temperature max value.
241
242 `temp[1-*]_min`
243 Temperature min value.
244
245 `temp[1-*]_max_hyst`
246 Temperature hysteresis value for max limit.
247
248 `temp[1-*]_min_hyst`
249 Temperature hysteresis value for min limit.
250
251 `temp[1-*]_input`
252 Temperature input value.
253
254 `temp[1-*]_crit`
255 Temperature critical max value, typically greater than
256 corresponding temp_max values.
257
258 `temp[1-*]_crit_hyst`
259 Temperature hysteresis value for critical limit.
260
261 `temp[1-*]_emergency`
262 Temperature emergency max value, for chips supporting more than
263 two upper temperature limits.
264
265 `temp[1-*]_emergency_hyst`
266 Temperature hysteresis value for emergency limit.
267
268 `temp[1-*]_lcrit`
269 Temperature critical min value, typically lower than
270 corresponding temp_min values.
271
272 `temp[1-*]_lcrit_hyst`
273 Temperature hysteresis value for critical min limit.
274
275 `temp[1-*]_offset`
276 Temperature offset which is added to the temperature reading
277 by the chip.
278
279 `temp[1-*]_label`
280 Suggested temperature channel label.
281
282 `temp[1-*]_lowest`
283 Historical minimum temperature
284
285 `temp[1-*]_highest`
286 Historical maximum temperature
287
288 `temp[1-*]_reset_history`
289 Reset temp_lowest and temp_highest
290
291 `temp_reset_history`
292 Reset temp_lowest and temp_highest for all sensors
293
294 `temp[1-*]_enable`
295 Enable or disable the sensors.
296
297 `temp[1-*]_rated_min`
298 Minimum rated temperature.
299
300 `temp[1-*]_rated_max`
301 Maximum rated temperature.
302
303 Some chips measure temperature using external thermistors and an ADC, and
304 report the temperature measurement as a voltage. Converting this voltage
305 back to a temperature (or the other way around for limits) requires
306 mathematical functions not available in the kernel, so the conversion
307 must occur in user space. For these chips, all temp* files described
308 above should contain values expressed in millivolt instead of millidegree
309 Celsius. In other words, such temperature channels are handled as voltage
310 channels by the driver.
311
312 Also see the Alarms section for status flags associated with temperatures.
313
314
315 ********
316 Currents
317 ********
318
319 `curr[1-*]_max`
320 Current max value.
321
322 `curr[1-*]_min`
323 Current min value.
324
325 `curr[1-*]_lcrit`
326 Current critical low value
327
328 `curr[1-*]_crit`
329 Current critical high value.
330
331 `curr[1-*]_input`
332 Current input value.
333
334 `curr[1-*]_average`
335 Average current use.
336
337 `curr[1-*]_lowest`
338 Historical minimum current.
339
340 `curr[1-*]_highest`
341 Historical maximum current.
342
343 `curr[1-*]_reset_history`
344 Reset currX_lowest and currX_highest
345
346 WO
347
348 `curr_reset_history`
349 Reset currX_lowest and currX_highest for all sensors.
350
351 `curr[1-*]_enable`
352 Enable or disable the sensors.
353
354 `curr[1-*]_rated_min`
355 Minimum rated current.
356
357 `curr[1-*]_rated_max`
358 Maximum rated current.
359
360 Also see the Alarms section for status flags associated with currents.
361
362 *****
363 Power
364 *****
365
366 `power[1-*]_average`
367 Average power use.
368
369 `power[1-*]_average_interval`
370 Power use averaging interval.
371
372 `power[1-*]_average_interval_max`
373 Maximum power use averaging interval.
374
375 `power[1-*]_average_interval_min`
376 Minimum power use averaging interval.
377
378 `power[1-*]_average_highest`
379 Historical average maximum power use
380
381 `power[1-*]_average_lowest`
382 Historical average minimum power use
383
384 `power[1-*]_average_max`
385 A poll notification is sent to `power[1-*]_average` when
386 power use rises above this value.
387
388 `power[1-*]_average_min`
389 A poll notification is sent to `power[1-*]_average` when
390 power use sinks below this value.
391
392 `power[1-*]_input`
393 Instantaneous power use.
394
395 `power[1-*]_input_highest`
396 Historical maximum power use
397
398 `power[1-*]_input_lowest`
399 Historical minimum power use.
400
401 `power[1-*]_reset_history`
402 Reset input_highest, input_lowest, average_highest and
403 average_lowest.
404
405 `power[1-*]_accuracy`
406 Accuracy of the power meter.
407
408 `power[1-*]_cap`
409 If power use rises above this limit, the
410 system should take action to reduce power use.
411
412 `power[1-*]_cap_hyst`
413 Margin of hysteresis built around capping and notification.
414
415 `power[1-*]_cap_max`
416 Maximum cap that can be set.
417
418 `power[1-*]_cap_min`
419 Minimum cap that can be set.
420
421 `power[1-*]_max`
422 Maximum power.
423
424 `power[1-*]_crit`
425 Critical maximum power.
426
427 If power rises to or above this limit, the
428 system is expected take drastic action to reduce
429 power consumption, such as a system shutdown or
430 a forced powerdown of some devices.
431
432 Unit: microWatt
433
434 RW
435
436 `power[1-*]_enable`
437 Enable or disable the sensors.
438
439 When disabled the sensor read will return
440 -ENODATA.
441
442 - 1: Enable
443 - 0: Disable
444
445 RW
446
447 `power[1-*]_rated_min`
448 Minimum rated power.
449
450 Unit: microWatt
451
452 RO
453
454 `power[1-*]_rated_max`
455 Maximum rated power.
456
457 Unit: microWatt
458
459 RO
460
461 Also see the Alarms section for status flags associated with power readings.
462
463 ******
464 Energy
465 ******
466
467 `energy[1-*]_input`
468 Cumulative energy use
469
470 Unit: microJoule
471
472 RO
473
474 `energy[1-*]_enable`
475 Enable or disable the sensors.
476
477 When disabled the sensor read will return
478 -ENODATA.
479
480 - 1: Enable
481 - 0: Disable
482
483 RW
484
485 ********
486 Humidity
487 ********
488
489 `humidity[1-*]_input`
490 Humidity.
491
492 `humidity[1-*]_enable`
493 Enable or disable the sensors.
494
495 `humidity[1-*]_rated_min`
496 Minimum rated humidity.
497
498 `humidity[1-*]_rated_max`
499 Maximum rated humidity.
500
501 ******
502 Alarms
503 ******
504
505 Each channel or limit may have an associated alarm file, containing a
506 boolean value. 1 means than an alarm condition exists, 0 means no alarm.
507
508 Usually a given chip will either use channel-related alarms, or
509 limit-related alarms, not both. The driver should just reflect the hardware
510 implementation.
511
512 +-------------------------------+-----------------------+
513 | **`in[0-*]_alarm`, | Channel alarm |
514 | `curr[1-*]_alarm`, | |
515 | `power[1-*]_alarm`, | - 0: no alarm |
516 | `fan[1-*]_alarm`, | - 1: alarm |
517 | `temp[1-*]_alarm`** | |
518 | | RO |
519 +-------------------------------+-----------------------+
520
521 **OR**
522
523 +-------------------------------+-----------------------+
524 | **`in[0-*]_min_alarm`, | Limit alarm |
525 | `in[0-*]_max_alarm`, | |
526 | `in[0-*]_lcrit_alarm`, | - 0: no alarm |
527 | `in[0-*]_crit_alarm`, | - 1: alarm |
528 | `curr[1-*]_min_alarm`, | |
529 | `curr[1-*]_max_alarm`, | RO |
530 | `curr[1-*]_lcrit_alarm`, | |
531 | `curr[1-*]_crit_alarm`, | |
532 | `power[1-*]_cap_alarm`, | |
533 | `power[1-*]_max_alarm`, | |
534 | `power[1-*]_crit_alarm`, | |
535 | `fan[1-*]_min_alarm`, | |
536 | `fan[1-*]_max_alarm`, | |
537 | `temp[1-*]_min_alarm`, | |
538 | `temp[1-*]_max_alarm`, | |
539 | `temp[1-*]_lcrit_alarm`, | |
540 | `temp[1-*]_crit_alarm`, | |
541 | `temp[1-*]_emergency_alarm`** | |
542 +-------------------------------+-----------------------+
543
544 Each input channel may have an associated fault file. This can be used
545 to notify open diodes, unconnected fans etc. where the hardware
546 supports it. When this boolean has value 1, the measurement for that
547 channel should not be trusted.
548
549 `fan[1-*]_fault` / `temp[1-*]_fault`
550 Input fault condition.
551
552 Some chips also offer the possibility to get beeped when an alarm occurs:
553
554 `beep_enable`
555 Master beep enable.
556
557 `in[0-*]_beep`, `curr[1-*]_beep`, `fan[1-*]_beep`, `temp[1-*]_beep`,
558 Channel beep.
559
560 In theory, a chip could provide per-limit beep masking, but no such chip
561 was seen so far.
562
563 Old drivers provided a different, non-standard interface to alarms and
564 beeps. These interface files are deprecated, but will be kept around
565 for compatibility reasons:
566
567 `alarms`
568 Alarm bitmask.
569
570 `beep_mask`
571 Bitmask for beep.
572
573
574 *******************
575 Intrusion detection
576 *******************
577
578 `intrusion[0-*]_alarm`
579 Chassis intrusion detection.
580
581 `intrusion[0-*]_beep`
582 Chassis intrusion beep.
583
584 ****************************
585 Average sample configuration
586 ****************************
587
588 Devices allowing for reading {in,power,curr,temp}_average values may export
589 attributes for controlling number of samples used to compute average.
590
591 +--------------+---------------------------------------------------------------+
592 | samples | Sets number of average samples for all types of measurements. |
593 | | |
594 | | RW |
595 +--------------+---------------------------------------------------------------+
596 | in_samples | Sets number of average samples for specific type of |
597 | power_samples| measurements. |
598 | curr_samples | |
599 | temp_samples | Note that on some devices it won't be possible to set all of |
600 | | them to different values so changing one might also change |
601 | | some others. |
602 | | |
603 | | RW |
604 +--------------+---------------------------------------------------------------+
605
606 sysfs attribute writes interpretation
607 -------------------------------------
608
609 hwmon sysfs attributes always contain numbers, so the first thing to do is to
610 convert the input to a number, there are 2 ways todo this depending whether
611 the number can be negative or not::
612
613 unsigned long u = simple_strtoul(buf, NULL, 10);
614 long s = simple_strtol(buf, NULL, 10);
615
616 With buf being the buffer with the user input being passed by the kernel.
617 Notice that we do not use the second argument of strto[u]l, and thus cannot
618 tell when 0 is returned, if this was really 0 or is caused by invalid input.
619 This is done deliberately as checking this everywhere would add a lot of
620 code to the kernel.
621
622 Notice that it is important to always store the converted value in an
623 unsigned long or long, so that no wrap around can happen before any further
624 checking.
625
626 After the input string is converted to an (unsigned) long, the value should be
627 checked if its acceptable. Be careful with further conversions on the value
628 before checking it for validity, as these conversions could still cause a wrap
629 around before the check. For example do not multiply the result, and only
630 add/subtract if it has been divided before the add/subtract.
631
632 What to do if a value is found to be invalid, depends on the type of the
633 sysfs attribute that is being set. If it is a continuous setting like a
634 tempX_max or inX_max attribute, then the value should be clamped to its
635 limits using clamp_val(value, min_limit, max_limit). If it is not continuous
636 like for example a tempX_type, then when an invalid value is written,
637 -EINVAL should be returned.
638
639 Example1, temp1_max, register is a signed 8 bit value (-128 - 127 degrees)::
640
641 long v = simple_strtol(buf, NULL, 10) / 1000;
642 v = clamp_val(v, -128, 127);
643 /* write v to register */
644
645 Example2, fan divider setting, valid values 2, 4 and 8::
646
647 unsigned long v = simple_strtoul(buf, NULL, 10);
648
649 switch (v) {
650 case 2: v = 1; break;
651 case 4: v = 2; break;
652 case 8: v = 3; break;
653 default:
654 return -EINVAL;
655 }
656 /* write v to register */
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