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
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.
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.
98 in[0-*]_min Voltage min value.
102 in[0-*]_max Voltage max value.
106 in[0-*]_input Voltage input value.
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
121 in[0-*]_label Suggested voltage channel label.
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
129 cpu[0-*]_vid CPU core reference voltage.
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
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.
149 fan[1-*]_min Fan minimum value
150 Unit: revolution/min (RPM)
153 fan[1-*]_input Fan input value.
154 Unit: revolution/min (RPM)
157 fan[1-*]_div Fan divisor.
158 Integer value in powers of two (1, 2, 4, 8, 16, 32, 64, 128).
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.
166 Unit: revolution/min (RPM)
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.
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.
178 Also see the Alarms section for status flags associated with fans.
185 pwm[1-*] Pulse width modulation fan control.
186 Integer value in the range 0 to 255
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
199 pwm[1-*]_mode 0: DC mode (direct current)
200 1: PWM mode (pulse-width modulation)
203 pwm[1-*]_freq Base PWM frequency in Hz.
204 Only possibly available when pwmN_mode is PWM, but not always
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.
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.
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.
237 temp[1-*]_type Sensor type selection.
246 Not all types are supported by all chips
248 temp[1-*]_max Temperature max value.
249 Unit: millidegree Celsius (or millivolt, see below)
252 temp[1-*]_min Temperature min value.
253 Unit: millidegree Celsius
257 Temperature hysteresis value for max limit.
258 Unit: millidegree Celsius
259 Must be reported as an absolute temperature, NOT a delta
263 temp[1-*]_input Temperature input value.
264 Unit: millidegree Celsius
267 temp[1-*]_crit Temperature critical value, typically greater than
268 corresponding temp_max values.
269 Unit: millidegree Celsius
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.
280 Temperature offset which is added to the temperature reading
282 Unit: millidegree Celsius
285 temp[1-*]_label Suggested temperature channel label.
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
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.
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
316 curr[1-*]_min Current min value.
320 curr[1-*]_input Current input value
328 power[1-*]_average Average power use
332 power[1-*]_average_highest Historical average maximum power use
336 power[1-*]_average_lowest Historical average minimum power use
340 power[1-*]_input Instantaneous power use
344 power[1-*]_input_highest Historical maximum power use
348 power[1-*]_input_lowest Historical minimum power use
352 power[1-*]_reset_history Reset input_highest, input_lowest,
353 average_highest and average_lowest.
360 Each channel or limit may have an associated alarm file, containing a
361 boolean value. 1 means than an alarm condition exists, 0 means no alarm.
363 Usually a given chip will either use channel-related alarms, or
364 limit-related alarms, not both. The driver should just reflect the hardware
388 Each input channel may have an associated fault file. This can be used
389 to notify open diodes, unconnected fans etc. where the hardware
390 supports it. When this boolean has value 1, the measurement for that
391 channel should not be trusted.
396 Input fault condition
401 Some chips also offer the possibility to get beeped when an alarm occurs:
403 beep_enable Master beep enable
416 In theory, a chip could provide per-limit beep masking, but no such chip
419 Old drivers provided a different, non-standard interface to alarms and
420 beeps. These interface files are deprecated, but will be kept around
421 for compatibility reasons:
423 alarms Alarm bitmask.
425 Integer representation of one to four bytes.
426 A '1' bit means an alarm.
427 Chips should be programmed for 'comparator' mode so that
428 the alarm will 'come back' after you read the register
429 if it is still valid.
430 Generally a direct representation of a chip's internal
431 alarm registers; there is no standard for the position
432 of individual bits. For this reason, the use of this
433 interface file for new drivers is discouraged. Use
434 individual *_alarm and *_fault files instead.
435 Bits are defined in kernel/include/sensors.h.
437 beep_mask Bitmask for beep.
438 Same format as 'alarms' with the same bit locations,
439 use discouraged for the same reason. Use individual
440 *_beep files instead.
444 sysfs attribute writes interpretation
445 -------------------------------------
447 hwmon sysfs attributes always contain numbers, so the first thing to do is to
448 convert the input to a number, there are 2 ways todo this depending whether
449 the number can be negative or not:
450 unsigned long u = simple_strtoul(buf, NULL, 10);
451 long s = simple_strtol(buf, NULL, 10);
453 With buf being the buffer with the user input being passed by the kernel.
454 Notice that we do not use the second argument of strto[u]l, and thus cannot
455 tell when 0 is returned, if this was really 0 or is caused by invalid input.
456 This is done deliberately as checking this everywhere would add a lot of
459 Notice that it is important to always store the converted value in an
460 unsigned long or long, so that no wrap around can happen before any further
463 After the input string is converted to an (unsigned) long, the value should be
464 checked if its acceptable. Be careful with further conversions on the value
465 before checking it for validity, as these conversions could still cause a wrap
466 around before the check. For example do not multiply the result, and only
467 add/subtract if it has been divided before the add/subtract.
469 What to do if a value is found to be invalid, depends on the type of the
470 sysfs attribute that is being set. If it is a continuous setting like a
471 tempX_max or inX_max attribute, then the value should be clamped to its
472 limits using SENSORS_LIMIT(value, min_limit, max_limit). If it is not
473 continuous like for example a tempX_type, then when an invalid value is
474 written, -EINVAL should be returned.
476 Example1, temp1_max, register is a signed 8 bit value (-128 - 127 degrees):
478 long v = simple_strtol(buf, NULL, 10) / 1000;
479 v = SENSORS_LIMIT(v, -128, 127);
480 /* write v to register */
482 Example2, fan divider setting, valid values 2, 4 and 8:
484 unsigned long v = simple_strtoul(buf, NULL, 10);
487 case 2: v = 1; break;
488 case 4: v = 2; break;
489 case 8: v = 3; break;
493 /* write v to register */
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