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
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.
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.
99 in[0-*]_min Voltage min value.
103 in[0-*]_max Voltage max value.
107 in[0-*]_input Voltage input value.
110 Voltage measured on the chip pin.
111 Actual voltage depends on the scaling resistors on the
112 motherboard, as recommended in the chip datasheet.
113 This varies by chip and by motherboard.
114 Because of this variation, values are generally NOT scaled
115 by the chip driver, and must be done by the application.
116 However, some drivers (notably lm87 and via686a)
117 do scale, because of internal resistors built into a chip.
118 These drivers will output the actual voltage. Rule of
119 thumb: drivers should report the voltage values at the
122 in[0-*]_label Suggested voltage channel label.
124 Should only be created if the driver has hints about what
125 this voltage channel is being used for, and user-space
126 doesn't. In all other cases, the label is provided by
130 cpu[0-*]_vid CPU core reference voltage.
135 vrm Voltage Regulator Module version number.
136 RW (but changing it should no more be necessary)
137 Originally the VRM standard version multiplied by 10, but now
138 an arbitrary number, as not all standards have a version
140 Affects the way the driver calculates the CPU core reference
141 voltage from the vid pins.
143 Also see the Alarms section for status flags associated with voltages.
150 fan[1-*]_min Fan minimum value
151 Unit: revolution/min (RPM)
154 fan[1-*]_max Fan maximum value
155 Unit: revolution/min (RPM)
156 Only rarely supported by the hardware.
159 fan[1-*]_input Fan input value.
160 Unit: revolution/min (RPM)
163 fan[1-*]_div Fan divisor.
164 Integer value in powers of two (1, 2, 4, 8, 16, 32, 64, 128).
166 Some chips only support values 1, 2, 4 and 8.
167 Note that this is actually an internal clock divisor, which
168 affects the measurable speed range, not the read value.
172 Unit: revolution/min (RPM)
174 Only makes sense if the chip supports closed-loop fan speed
175 control based on the measured fan speed.
177 fan[1-*]_label Suggested fan channel label.
179 Should only be created if the driver has hints about what
180 this fan channel is being used for, and user-space doesn't.
181 In all other cases, the label is provided by user-space.
184 Also see the Alarms section for status flags associated with fans.
191 pwm[1-*] Pulse width modulation fan control.
192 Integer value in the range 0 to 255
197 Fan speed control method:
198 0: no fan speed control (i.e. fan at full speed)
199 1: manual fan speed control enabled (using pwm[1-*])
200 2+: automatic fan speed control enabled
201 Check individual chip documentation files for automatic mode
205 pwm[1-*]_mode 0: DC mode (direct current)
206 1: PWM mode (pulse-width modulation)
209 pwm[1-*]_freq Base PWM frequency in Hz.
210 Only possibly available when pwmN_mode is PWM, but not always
214 pwm[1-*]_auto_channels_temp
215 Select which temperature channels affect this PWM output in
216 auto mode. Bitfield, 1 is temp1, 2 is temp2, 4 is temp3 etc...
217 Which values are possible depend on the chip used.
220 pwm[1-*]_auto_point[1-*]_pwm
221 pwm[1-*]_auto_point[1-*]_temp
222 pwm[1-*]_auto_point[1-*]_temp_hyst
223 Define the PWM vs temperature curve. Number of trip points is
224 chip-dependent. Use this for chips which associate trip points
225 to PWM output channels.
228 temp[1-*]_auto_point[1-*]_pwm
229 temp[1-*]_auto_point[1-*]_temp
230 temp[1-*]_auto_point[1-*]_temp_hyst
231 Define the PWM vs temperature curve. Number of trip points is
232 chip-dependent. Use this for chips which associate trip points
233 to temperature channels.
236 There is a third case where trip points are associated to both PWM output
237 channels and temperature channels: the PWM values are associated to PWM
238 output channels while the temperature values are associated to temperature
239 channels. In that case, the result is determined by the mapping between
240 temperature inputs and PWM outputs. When several temperature inputs are
241 mapped to a given PWM output, this leads to several candidate PWM values.
242 The actual result is up to the chip, but in general the highest candidate
243 value (fastest fan speed) wins.
250 temp[1-*]_type Sensor type selection.
259 Not all types are supported by all chips
261 temp[1-*]_max Temperature max value.
262 Unit: millidegree Celsius (or millivolt, see below)
265 temp[1-*]_min Temperature min value.
266 Unit: millidegree Celsius
270 Temperature hysteresis value for max limit.
271 Unit: millidegree Celsius
272 Must be reported as an absolute temperature, NOT a delta
276 temp[1-*]_input Temperature input value.
277 Unit: millidegree Celsius
280 temp[1-*]_crit Temperature critical value, typically greater than
281 corresponding temp_max values.
282 Unit: millidegree Celsius
286 Temperature hysteresis value for critical limit.
287 Unit: millidegree Celsius
288 Must be reported as an absolute temperature, NOT a delta
289 from the critical value.
293 Temperature offset which is added to the temperature reading
295 Unit: millidegree Celsius
298 temp[1-*]_label Suggested temperature channel label.
300 Should only be created if the driver has hints about what
301 this temperature channel is being used for, and user-space
302 doesn't. In all other cases, the label is provided by
307 Historical minimum temperature
308 Unit: millidegree Celsius
312 Historical maximum temperature
313 Unit: millidegree Celsius
316 temp[1-*]_reset_history
317 Reset temp_lowest and temp_highest
321 Reset temp_lowest and temp_highest for all sensors
324 Some chips measure temperature using external thermistors and an ADC, and
325 report the temperature measurement as a voltage. Converting this voltage
326 back to a temperature (or the other way around for limits) requires
327 mathematical functions not available in the kernel, so the conversion
328 must occur in user space. For these chips, all temp* files described
329 above should contain values expressed in millivolt instead of millidegree
330 Celsius. In other words, such temperature channels are handled as voltage
331 channels by the driver.
333 Also see the Alarms section for status flags associated with temperatures.
340 Note that no known chip provides current measurements as of writing,
341 so this part is theoretical, so to say.
343 curr[1-*]_max Current max value
347 curr[1-*]_min Current min value.
351 curr[1-*]_input Current input value
359 power[1-*]_average Average power use
363 power[1-*]_average_interval Power use averaging interval. A poll
364 notification is sent to this file if the
365 hardware changes the averaging interval.
369 power[1-*]_average_interval_max Maximum power use averaging interval
373 power[1-*]_average_interval_min Minimum power use averaging interval
377 power[1-*]_average_highest Historical average maximum power use
381 power[1-*]_average_lowest Historical average minimum power use
385 power[1-*]_average_max A poll notification is sent to
386 power[1-*]_average when power use
387 rises above this value.
391 power[1-*]_average_min A poll notification is sent to
392 power[1-*]_average when power use
393 sinks below this value.
397 power[1-*]_input Instantaneous power use
401 power[1-*]_input_highest Historical maximum power use
405 power[1-*]_input_lowest Historical minimum power use
409 power[1-*]_reset_history Reset input_highest, input_lowest,
410 average_highest and average_lowest.
413 power[1-*]_accuracy Accuracy of the power meter.
417 power[1-*]_alarm 1 if the system is drawing more power than the
418 cap allows; 0 otherwise. A poll notification is
419 sent to this file when the power use exceeds the
420 cap. This file only appears if the cap is known
421 to be enforced by hardware.
424 power[1-*]_cap If power use rises above this limit, the
425 system should take action to reduce power use.
426 A poll notification is sent to this file if the
427 cap is changed by the hardware. The *_cap
428 files only appear if the cap is known to be
429 enforced by hardware.
433 power[1-*]_cap_hyst Margin of hysteresis built around capping and
438 power[1-*]_cap_max Maximum cap that can be set.
442 power[1-*]_cap_min Minimum cap that can be set.
450 energy[1-*]_input Cumulative energy use
459 Each channel or limit may have an associated alarm file, containing a
460 boolean value. 1 means than an alarm condition exists, 0 means no alarm.
462 Usually a given chip will either use channel-related alarms, or
463 limit-related alarms, not both. The driver should just reflect the hardware
488 Each input channel may have an associated fault file. This can be used
489 to notify open diodes, unconnected fans etc. where the hardware
490 supports it. When this boolean has value 1, the measurement for that
491 channel should not be trusted.
496 Input fault condition
501 Some chips also offer the possibility to get beeped when an alarm occurs:
503 beep_enable Master beep enable
516 In theory, a chip could provide per-limit beep masking, but no such chip
519 Old drivers provided a different, non-standard interface to alarms and
520 beeps. These interface files are deprecated, but will be kept around
521 for compatibility reasons:
523 alarms Alarm bitmask.
525 Integer representation of one to four bytes.
526 A '1' bit means an alarm.
527 Chips should be programmed for 'comparator' mode so that
528 the alarm will 'come back' after you read the register
529 if it is still valid.
530 Generally a direct representation of a chip's internal
531 alarm registers; there is no standard for the position
532 of individual bits. For this reason, the use of this
533 interface file for new drivers is discouraged. Use
534 individual *_alarm and *_fault files instead.
535 Bits are defined in kernel/include/sensors.h.
537 beep_mask Bitmask for beep.
538 Same format as 'alarms' with the same bit locations,
539 use discouraged for the same reason. Use individual
540 *_beep files instead.
544 ***********************
545 * Intrusion detection *
546 ***********************
549 Chassis intrusion detection
551 1: intrusion detected
553 Contrary to regular alarm flags which clear themselves
554 automatically when read, this one sticks until cleared by
555 the user. This is done by writing 0 to the file. Writing
556 other values is unsupported.
559 Chassis intrusion beep
565 sysfs attribute writes interpretation
566 -------------------------------------
568 hwmon sysfs attributes always contain numbers, so the first thing to do is to
569 convert the input to a number, there are 2 ways todo this depending whether
570 the number can be negative or not:
571 unsigned long u = simple_strtoul(buf, NULL, 10);
572 long s = simple_strtol(buf, NULL, 10);
574 With buf being the buffer with the user input being passed by the kernel.
575 Notice that we do not use the second argument of strto[u]l, and thus cannot
576 tell when 0 is returned, if this was really 0 or is caused by invalid input.
577 This is done deliberately as checking this everywhere would add a lot of
580 Notice that it is important to always store the converted value in an
581 unsigned long or long, so that no wrap around can happen before any further
584 After the input string is converted to an (unsigned) long, the value should be
585 checked if its acceptable. Be careful with further conversions on the value
586 before checking it for validity, as these conversions could still cause a wrap
587 around before the check. For example do not multiply the result, and only
588 add/subtract if it has been divided before the add/subtract.
590 What to do if a value is found to be invalid, depends on the type of the
591 sysfs attribute that is being set. If it is a continuous setting like a
592 tempX_max or inX_max attribute, then the value should be clamped to its
593 limits using SENSORS_LIMIT(value, min_limit, max_limit). If it is not
594 continuous like for example a tempX_type, then when an invalid value is
595 written, -EINVAL should be returned.
597 Example1, temp1_max, register is a signed 8 bit value (-128 - 127 degrees):
599 long v = simple_strtol(buf, NULL, 10) / 1000;
600 v = SENSORS_LIMIT(v, -128, 127);
601 /* write v to register */
603 Example2, fan divider setting, valid values 2, 4 and 8:
605 unsigned long v = simple_strtoul(buf, NULL, 10);
608 case 2: v = 1; break;
609 case 4: v = 2; break;
610 case 8: v = 3; break;
614 /* write v to register */
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