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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 RW read/write value
75 Read/write values may be read-only for some chips, depending on the
76 hardware implementation.
78 All entries (except name) are optional, and should only be created in a
79 given driver if the chip has the feature.
82 ********
83 * Name *
84 ********
86 name The chip name.
87 This should be a short, lowercase string, not containing
88 spaces nor dashes, representing the chip name. This is
89 the only mandatory attribute.
90 I2C devices get this attribute created automatically.
91 RO
94 ************
95 * Voltages *
96 ************
98 in[0-*]_min Voltage min value.
99 Unit: millivolt
100 RW
102 in[0-*]_max Voltage max value.
103 Unit: millivolt
104 RW
106 in[0-*]_input Voltage input value.
107 Unit: millivolt
108 RO
109 Voltage measured on the chip pin.
110 Actual voltage depends on the scaling resistors on the
111 motherboard, as recommended in the chip datasheet.
112 This varies by chip and by motherboard.
113 Because of this variation, values are generally NOT scaled
114 by the chip driver, and must be done by the application.
115 However, some drivers (notably lm87 and via686a)
116 do scale, because of internal resistors built into a chip.
117 These drivers will output the actual voltage. Rule of
118 thumb: drivers should report the voltage values at the
119 "pins" of the chip.
121 in[0-*]_label Suggested voltage channel label.
122 Text string
123 Should only be created if the driver has hints about what
124 this voltage channel is being used for, and user-space
125 doesn't. In all other cases, the label is provided by
126 user-space.
127 RO
129 cpu[0-*]_vid CPU core reference voltage.
130 Unit: millivolt
131 RO
132 Not always correct.
134 vrm Voltage Regulator Module version number.
135 RW (but changing it should no more be necessary)
136 Originally the VRM standard version multiplied by 10, but now
137 an arbitrary number, as not all standards have a version
138 number.
139 Affects the way the driver calculates the CPU core reference
140 voltage from the vid pins.
142 Also see the Alarms section for status flags associated with voltages.
145 ********
146 * Fans *
147 ********
149 fan[1-*]_min Fan minimum value
150 Unit: revolution/min (RPM)
151 RW
153 fan[1-*]_input Fan input value.
154 Unit: revolution/min (RPM)
155 RO
157 fan[1-*]_div Fan divisor.
158 Integer value in powers of two (1, 2, 4, 8, 16, 32, 64, 128).
159 RW
160 Some chips only support values 1, 2, 4 and 8.
161 Note that this is actually an internal clock divisor, which
162 affects the measurable speed range, not the read value.
164 fan[1-*]_target
165 Desired fan speed
166 Unit: revolution/min (RPM)
167 RW
168 Only makes sense if the chip supports closed-loop fan speed
169 control based on the measured fan speed.
171 fan[1-*]_label Suggested fan channel label.
172 Text string
173 Should only be created if the driver has hints about what
174 this fan channel is being used for, and user-space doesn't.
175 In all other cases, the label is provided by user-space.
176 RO
178 Also see the Alarms section for status flags associated with fans.
181 *******
182 * PWM *
183 *******
185 pwm[1-*] Pulse width modulation fan control.
186 Integer value in the range 0 to 255
187 RW
188 255 is max or 100%.
190 pwm[1-*]_enable
191 Fan speed control method:
192 0: no fan speed control (i.e. fan at full speed)
193 1: manual fan speed control enabled (using pwm[1-*])
194 2+: automatic fan speed control enabled
195 Check individual chip documentation files for automatic mode
196 details.
197 RW
199 pwm[1-*]_mode 0: DC mode (direct current)
200 1: PWM mode (pulse-width modulation)
201 RW
203 pwm[1-*]_freq Base PWM frequency in Hz.
204 Only possibly available when pwmN_mode is PWM, but not always
205 present even then.
206 RW
208 pwm[1-*]_auto_channels_temp
209 Select which temperature channels affect this PWM output in
210 auto mode. Bitfield, 1 is temp1, 2 is temp2, 4 is temp3 etc...
211 Which values are possible depend on the chip used.
212 RW
214 pwm[1-*]_auto_point[1-*]_pwm
215 pwm[1-*]_auto_point[1-*]_temp
216 pwm[1-*]_auto_point[1-*]_temp_hyst
217 Define the PWM vs temperature curve. Number of trip points is
218 chip-dependent. Use this for chips which associate trip points
219 to PWM output channels.
220 RW
222 OR
224 temp[1-*]_auto_point[1-*]_pwm
225 temp[1-*]_auto_point[1-*]_temp
226 temp[1-*]_auto_point[1-*]_temp_hyst
227 Define the PWM vs temperature curve. Number of trip points is
228 chip-dependent. Use this for chips which associate trip points
229 to temperature channels.
230 RW
233 ****************
234 * Temperatures *
235 ****************
237 temp[1-*]_type Sensor type selection.
238 Integers 1 to 6
239 RW
240 1: PII/Celeron Diode
241 2: 3904 transistor
242 3: thermal diode
243 4: thermistor
244 5: AMD AMDSI
245 6: Intel PECI
246 Not all types are supported by all chips
248 temp[1-*]_max Temperature max value.
249 Unit: millidegree Celsius (or millivolt, see below)
250 RW
252 temp[1-*]_min Temperature min value.
253 Unit: millidegree Celsius
254 RW
256 temp[1-*]_max_hyst
257 Temperature hysteresis value for max limit.
258 Unit: millidegree Celsius
259 Must be reported as an absolute temperature, NOT a delta
260 from the max value.
261 RW
263 temp[1-*]_input Temperature input value.
264 Unit: millidegree Celsius
265 RO
267 temp[1-*]_crit Temperature critical value, typically greater than
268 corresponding temp_max values.
269 Unit: millidegree Celsius
270 RW
272 temp[1-*]_crit_hyst
273 Temperature hysteresis value for critical limit.
274 Unit: millidegree Celsius
275 Must be reported as an absolute temperature, NOT a delta
276 from the critical value.
277 RW
279 temp[1-*]_offset
280 Temperature offset which is added to the temperature reading
281 by the chip.
282 Unit: millidegree Celsius
283 Read/Write value.
285 temp[1-*]_label Suggested temperature channel label.
286 Text string
287 Should only be created if the driver has hints about what
288 this temperature channel is being used for, and user-space
289 doesn't. In all other cases, the label is provided by
290 user-space.
291 RO
293 Some chips measure temperature using external thermistors and an ADC, and
294 report the temperature measurement as a voltage. Converting this voltage
295 back to a temperature (or the other way around for limits) requires
296 mathematical functions not available in the kernel, so the conversion
297 must occur in user space. For these chips, all temp* files described
298 above should contain values expressed in millivolt instead of millidegree
299 Celsius. In other words, such temperature channels are handled as voltage
300 channels by the driver.
302 Also see the Alarms section for status flags associated with temperatures.
305 ************
306 * Currents *
307 ************
309 Note that no known chip provides current measurements as of writing,
310 so this part is theoretical, so to say.
312 curr[1-*]_max Current max value
313 Unit: milliampere
314 RW
316 curr[1-*]_min Current min value.
317 Unit: milliampere
318 RW
320 curr[1-*]_input Current input value
321 Unit: milliampere
322 RO
324 *********
325 * Power *
326 *********
328 power[1-*]_average Average power use
329 Unit: microWatt
330 RO
332 power[1-*]_average_interval Power use averaging interval
333 Unit: milliseconds
334 RW
336 power[1-*]_average_highest Historical average maximum power use
337 Unit: microWatt
338 RO
340 power[1-*]_average_lowest Historical average minimum power use
341 Unit: microWatt
342 RO
344 power[1-*]_input Instantaneous power use
345 Unit: microWatt
346 RO
348 power[1-*]_input_highest Historical maximum power use
349 Unit: microWatt
350 RO
352 power[1-*]_input_lowest Historical minimum power use
353 Unit: microWatt
354 RO
356 power[1-*]_reset_history Reset input_highest, input_lowest,
357 average_highest and average_lowest.
358 WO
360 **********
361 * Energy *
362 **********
364 energy[1-*]_input Cumulative energy use
365 Unit: microJoule
366 RO
369 **********
370 * Alarms *
371 **********
373 Each channel or limit may have an associated alarm file, containing a
374 boolean value. 1 means than an alarm condition exists, 0 means no alarm.
376 Usually a given chip will either use channel-related alarms, or
377 limit-related alarms, not both. The driver should just reflect the hardware
378 implementation.
380 in[0-*]_alarm
381 fan[1-*]_alarm
382 temp[1-*]_alarm
383 Channel alarm
384 0: no alarm
385 1: alarm
386 RO
388 OR
390 in[0-*]_min_alarm
391 in[0-*]_max_alarm
392 fan[1-*]_min_alarm
393 temp[1-*]_min_alarm
394 temp[1-*]_max_alarm
395 temp[1-*]_crit_alarm
396 Limit alarm
397 0: no alarm
398 1: alarm
399 RO
401 Each input channel may have an associated fault file. This can be used
402 to notify open diodes, unconnected fans etc. where the hardware
403 supports it. When this boolean has value 1, the measurement for that
404 channel should not be trusted.
406 in[0-*]_fault
407 fan[1-*]_fault
408 temp[1-*]_fault
409 Input fault condition
410 0: no fault occured
411 1: fault condition
412 RO
414 Some chips also offer the possibility to get beeped when an alarm occurs:
416 beep_enable Master beep enable
417 0: no beeps
418 1: beeps
419 RW
421 in[0-*]_beep
422 fan[1-*]_beep
423 temp[1-*]_beep
424 Channel beep
425 0: disable
426 1: enable
427 RW
429 In theory, a chip could provide per-limit beep masking, but no such chip
430 was seen so far.
432 Old drivers provided a different, non-standard interface to alarms and
433 beeps. These interface files are deprecated, but will be kept around
434 for compatibility reasons:
436 alarms Alarm bitmask.
437 RO
438 Integer representation of one to four bytes.
439 A '1' bit means an alarm.
440 Chips should be programmed for 'comparator' mode so that
441 the alarm will 'come back' after you read the register
442 if it is still valid.
443 Generally a direct representation of a chip's internal
444 alarm registers; there is no standard for the position
445 of individual bits. For this reason, the use of this
446 interface file for new drivers is discouraged. Use
447 individual *_alarm and *_fault files instead.
448 Bits are defined in kernel/include/sensors.h.
450 beep_mask Bitmask for beep.
451 Same format as 'alarms' with the same bit locations,
452 use discouraged for the same reason. Use individual
453 *_beep files instead.
454 RW
457 ***********************
458 * Intrusion detection *
459 ***********************
461 intrusion[0-*]_alarm
462 Chassis intrusion detection
463 0: OK
464 1: intrusion detected
465 RW
466 Contrary to regular alarm flags which clear themselves
467 automatically when read, this one sticks until cleared by
468 the user. This is done by writing 0 to the file. Writing
469 other values is unsupported.
471 intrusion[0-*]_beep
472 Chassis intrusion beep
473 0: disable
474 1: enable
475 RW
478 sysfs attribute writes interpretation
479 -------------------------------------
481 hwmon sysfs attributes always contain numbers, so the first thing to do is to
482 convert the input to a number, there are 2 ways todo this depending whether
483 the number can be negative or not:
484 unsigned long u = simple_strtoul(buf, NULL, 10);
485 long s = simple_strtol(buf, NULL, 10);
487 With buf being the buffer with the user input being passed by the kernel.
488 Notice that we do not use the second argument of strto[u]l, and thus cannot
489 tell when 0 is returned, if this was really 0 or is caused by invalid input.
490 This is done deliberately as checking this everywhere would add a lot of
491 code to the kernel.
493 Notice that it is important to always store the converted value in an
494 unsigned long or long, so that no wrap around can happen before any further
495 checking.
497 After the input string is converted to an (unsigned) long, the value should be
498 checked if its acceptable. Be careful with further conversions on the value
499 before checking it for validity, as these conversions could still cause a wrap
500 around before the check. For example do not multiply the result, and only
501 add/subtract if it has been divided before the add/subtract.
503 What to do if a value is found to be invalid, depends on the type of the
504 sysfs attribute that is being set. If it is a continuous setting like a
505 tempX_max or inX_max attribute, then the value should be clamped to its
506 limits using SENSORS_LIMIT(value, min_limit, max_limit). If it is not
507 continuous like for example a tempX_type, then when an invalid value is
508 written, -EINVAL should be returned.
510 Example1, temp1_max, register is a signed 8 bit value (-128 - 127 degrees):
512 long v = simple_strtol(buf, NULL, 10) / 1000;
513 v = SENSORS_LIMIT(v, -128, 127);
514 /* write v to register */
516 Example2, fan divider setting, valid values 2, 4 and 8:
518 unsigned long v = simple_strtoul(buf, NULL, 10);
520 switch (v) {
521 case 2: v = 1; break;
522 case 4: v = 2; break;
523 case 8: v = 3; break;
524 default:
525 return -EINVAL;
526 }
527 /* write v to register */