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.
94 update_rate The rate at which the chip will update readings.
97 Some devices have a variable update rate. This attribute
98 can be used to change the update rate to the desired
106 in[0-*]_min Voltage min value.
110 in[0-*]_max Voltage max value.
114 in[0-*]_input Voltage input value.
117 Voltage measured on the chip pin.
118 Actual voltage depends on the scaling resistors on the
119 motherboard, as recommended in the chip datasheet.
120 This varies by chip and by motherboard.
121 Because of this variation, values are generally NOT scaled
122 by the chip driver, and must be done by the application.
123 However, some drivers (notably lm87 and via686a)
124 do scale, because of internal resistors built into a chip.
125 These drivers will output the actual voltage. Rule of
126 thumb: drivers should report the voltage values at the
129 in[0-*]_label Suggested voltage channel label.
131 Should only be created if the driver has hints about what
132 this voltage channel is being used for, and user-space
133 doesn't. In all other cases, the label is provided by
137 cpu[0-*]_vid CPU core reference voltage.
142 vrm Voltage Regulator Module version number.
143 RW (but changing it should no more be necessary)
144 Originally the VRM standard version multiplied by 10, but now
145 an arbitrary number, as not all standards have a version
147 Affects the way the driver calculates the CPU core reference
148 voltage from the vid pins.
150 Also see the Alarms section for status flags associated with voltages.
157 fan[1-*]_min Fan minimum value
158 Unit: revolution/min (RPM)
161 fan[1-*]_max Fan maximum value
162 Unit: revolution/min (RPM)
163 Only rarely supported by the hardware.
166 fan[1-*]_input Fan input value.
167 Unit: revolution/min (RPM)
170 fan[1-*]_div Fan divisor.
171 Integer value in powers of two (1, 2, 4, 8, 16, 32, 64, 128).
173 Some chips only support values 1, 2, 4 and 8.
174 Note that this is actually an internal clock divisor, which
175 affects the measurable speed range, not the read value.
179 Unit: revolution/min (RPM)
181 Only makes sense if the chip supports closed-loop fan speed
182 control based on the measured fan speed.
184 fan[1-*]_label Suggested fan channel label.
186 Should only be created if the driver has hints about what
187 this fan channel is being used for, and user-space doesn't.
188 In all other cases, the label is provided by user-space.
191 Also see the Alarms section for status flags associated with fans.
198 pwm[1-*] Pulse width modulation fan control.
199 Integer value in the range 0 to 255
204 Fan speed control method:
205 0: no fan speed control (i.e. fan at full speed)
206 1: manual fan speed control enabled (using pwm[1-*])
207 2+: automatic fan speed control enabled
208 Check individual chip documentation files for automatic mode
212 pwm[1-*]_mode 0: DC mode (direct current)
213 1: PWM mode (pulse-width modulation)
216 pwm[1-*]_freq Base PWM frequency in Hz.
217 Only possibly available when pwmN_mode is PWM, but not always
221 pwm[1-*]_auto_channels_temp
222 Select which temperature channels affect this PWM output in
223 auto mode. Bitfield, 1 is temp1, 2 is temp2, 4 is temp3 etc...
224 Which values are possible depend on the chip used.
227 pwm[1-*]_auto_point[1-*]_pwm
228 pwm[1-*]_auto_point[1-*]_temp
229 pwm[1-*]_auto_point[1-*]_temp_hyst
230 Define the PWM vs temperature curve. Number of trip points is
231 chip-dependent. Use this for chips which associate trip points
232 to PWM output channels.
235 temp[1-*]_auto_point[1-*]_pwm
236 temp[1-*]_auto_point[1-*]_temp
237 temp[1-*]_auto_point[1-*]_temp_hyst
238 Define the PWM vs temperature curve. Number of trip points is
239 chip-dependent. Use this for chips which associate trip points
240 to temperature channels.
243 There is a third case where trip points are associated to both PWM output
244 channels and temperature channels: the PWM values are associated to PWM
245 output channels while the temperature values are associated to temperature
246 channels. In that case, the result is determined by the mapping between
247 temperature inputs and PWM outputs. When several temperature inputs are
248 mapped to a given PWM output, this leads to several candidate PWM values.
249 The actual result is up to the chip, but in general the highest candidate
250 value (fastest fan speed) wins.
257 temp[1-*]_type Sensor type selection.
266 Not all types are supported by all chips
268 temp[1-*]_max Temperature max value.
269 Unit: millidegree Celsius (or millivolt, see below)
272 temp[1-*]_min Temperature min value.
273 Unit: millidegree Celsius
277 Temperature hysteresis value for max limit.
278 Unit: millidegree Celsius
279 Must be reported as an absolute temperature, NOT a delta
283 temp[1-*]_input Temperature input value.
284 Unit: millidegree Celsius
287 temp[1-*]_crit Temperature critical value, typically greater than
288 corresponding temp_max values.
289 Unit: millidegree Celsius
293 Temperature hysteresis value for critical limit.
294 Unit: millidegree Celsius
295 Must be reported as an absolute temperature, NOT a delta
296 from the critical value.
300 Temperature offset which is added to the temperature reading
302 Unit: millidegree Celsius
305 temp[1-*]_label Suggested temperature channel label.
307 Should only be created if the driver has hints about what
308 this temperature channel is being used for, and user-space
309 doesn't. In all other cases, the label is provided by
314 Historical minimum temperature
315 Unit: millidegree Celsius
319 Historical maximum temperature
320 Unit: millidegree Celsius
323 temp[1-*]_reset_history
324 Reset temp_lowest and temp_highest
328 Reset temp_lowest and temp_highest for all sensors
331 Some chips measure temperature using external thermistors and an ADC, and
332 report the temperature measurement as a voltage. Converting this voltage
333 back to a temperature (or the other way around for limits) requires
334 mathematical functions not available in the kernel, so the conversion
335 must occur in user space. For these chips, all temp* files described
336 above should contain values expressed in millivolt instead of millidegree
337 Celsius. In other words, such temperature channels are handled as voltage
338 channels by the driver.
340 Also see the Alarms section for status flags associated with temperatures.
347 Note that no known chip provides current measurements as of writing,
348 so this part is theoretical, so to say.
350 curr[1-*]_max Current max value
354 curr[1-*]_min Current min value.
358 curr[1-*]_input Current input value
366 power[1-*]_average Average power use
370 power[1-*]_average_interval Power use averaging interval. A poll
371 notification is sent to this file if the
372 hardware changes the averaging interval.
376 power[1-*]_average_interval_max Maximum power use averaging interval
380 power[1-*]_average_interval_min Minimum power use averaging interval
384 power[1-*]_average_highest Historical average maximum power use
388 power[1-*]_average_lowest Historical average minimum power use
392 power[1-*]_average_max A poll notification is sent to
393 power[1-*]_average when power use
394 rises above this value.
398 power[1-*]_average_min A poll notification is sent to
399 power[1-*]_average when power use
400 sinks below this value.
404 power[1-*]_input Instantaneous power use
408 power[1-*]_input_highest Historical maximum power use
412 power[1-*]_input_lowest Historical minimum power use
416 power[1-*]_reset_history Reset input_highest, input_lowest,
417 average_highest and average_lowest.
420 power[1-*]_accuracy Accuracy of the power meter.
424 power[1-*]_alarm 1 if the system is drawing more power than the
425 cap allows; 0 otherwise. A poll notification is
426 sent to this file when the power use exceeds the
427 cap. This file only appears if the cap is known
428 to be enforced by hardware.
431 power[1-*]_cap If power use rises above this limit, the
432 system should take action to reduce power use.
433 A poll notification is sent to this file if the
434 cap is changed by the hardware. The *_cap
435 files only appear if the cap is known to be
436 enforced by hardware.
440 power[1-*]_cap_hyst Margin of hysteresis built around capping and
445 power[1-*]_cap_max Maximum cap that can be set.
449 power[1-*]_cap_min Minimum cap that can be set.
457 energy[1-*]_input Cumulative energy use
466 Each channel or limit may have an associated alarm file, containing a
467 boolean value. 1 means than an alarm condition exists, 0 means no alarm.
469 Usually a given chip will either use channel-related alarms, or
470 limit-related alarms, not both. The driver should just reflect the hardware
495 Each input channel may have an associated fault file. This can be used
496 to notify open diodes, unconnected fans etc. where the hardware
497 supports it. When this boolean has value 1, the measurement for that
498 channel should not be trusted.
503 Input fault condition
508 Some chips also offer the possibility to get beeped when an alarm occurs:
510 beep_enable Master beep enable
523 In theory, a chip could provide per-limit beep masking, but no such chip
526 Old drivers provided a different, non-standard interface to alarms and
527 beeps. These interface files are deprecated, but will be kept around
528 for compatibility reasons:
530 alarms Alarm bitmask.
532 Integer representation of one to four bytes.
533 A '1' bit means an alarm.
534 Chips should be programmed for 'comparator' mode so that
535 the alarm will 'come back' after you read the register
536 if it is still valid.
537 Generally a direct representation of a chip's internal
538 alarm registers; there is no standard for the position
539 of individual bits. For this reason, the use of this
540 interface file for new drivers is discouraged. Use
541 individual *_alarm and *_fault files instead.
542 Bits are defined in kernel/include/sensors.h.
544 beep_mask Bitmask for beep.
545 Same format as 'alarms' with the same bit locations,
546 use discouraged for the same reason. Use individual
547 *_beep files instead.
551 ***********************
552 * Intrusion detection *
553 ***********************
556 Chassis intrusion detection
558 1: intrusion detected
560 Contrary to regular alarm flags which clear themselves
561 automatically when read, this one sticks until cleared by
562 the user. This is done by writing 0 to the file. Writing
563 other values is unsupported.
566 Chassis intrusion beep
572 sysfs attribute writes interpretation
573 -------------------------------------
575 hwmon sysfs attributes always contain numbers, so the first thing to do is to
576 convert the input to a number, there are 2 ways todo this depending whether
577 the number can be negative or not:
578 unsigned long u = simple_strtoul(buf, NULL, 10);
579 long s = simple_strtol(buf, NULL, 10);
581 With buf being the buffer with the user input being passed by the kernel.
582 Notice that we do not use the second argument of strto[u]l, and thus cannot
583 tell when 0 is returned, if this was really 0 or is caused by invalid input.
584 This is done deliberately as checking this everywhere would add a lot of
587 Notice that it is important to always store the converted value in an
588 unsigned long or long, so that no wrap around can happen before any further
591 After the input string is converted to an (unsigned) long, the value should be
592 checked if its acceptable. Be careful with further conversions on the value
593 before checking it for validity, as these conversions could still cause a wrap
594 around before the check. For example do not multiply the result, and only
595 add/subtract if it has been divided before the add/subtract.
597 What to do if a value is found to be invalid, depends on the type of the
598 sysfs attribute that is being set. If it is a continuous setting like a
599 tempX_max or inX_max attribute, then the value should be clamped to its
600 limits using SENSORS_LIMIT(value, min_limit, max_limit). If it is not
601 continuous like for example a tempX_type, then when an invalid value is
602 written, -EINVAL should be returned.
604 Example1, temp1_max, register is a signed 8 bit value (-128 - 127 degrees):
606 long v = simple_strtol(buf, NULL, 10) / 1000;
607 v = SENSORS_LIMIT(v, -128, 127);
608 /* write v to register */
610 Example2, fan divider setting, valid values 2, 4 and 8:
612 unsigned long v = simple_strtoul(buf, NULL, 10);
615 case 2: v = 1; break;
616 case 4: v = 2; break;
617 case 8: v = 3; break;
621 /* write v to register */
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