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-*]_max Fan maximum value
154 Unit: revolution/min (RPM)
155 Only rarely supported by the hardware.
158 fan[1-*]_input Fan input value.
159 Unit: revolution/min (RPM)
162 fan[1-*]_div Fan divisor.
163 Integer value in powers of two (1, 2, 4, 8, 16, 32, 64, 128).
165 Some chips only support values 1, 2, 4 and 8.
166 Note that this is actually an internal clock divisor, which
167 affects the measurable speed range, not the read value.
171 Unit: revolution/min (RPM)
173 Only makes sense if the chip supports closed-loop fan speed
174 control based on the measured fan speed.
176 fan[1-*]_label Suggested fan channel label.
178 Should only be created if the driver has hints about what
179 this fan channel is being used for, and user-space doesn't.
180 In all other cases, the label is provided by user-space.
183 Also see the Alarms section for status flags associated with fans.
190 pwm[1-*] Pulse width modulation fan control.
191 Integer value in the range 0 to 255
196 Fan speed control method:
197 0: no fan speed control (i.e. fan at full speed)
198 1: manual fan speed control enabled (using pwm[1-*])
199 2+: automatic fan speed control enabled
200 Check individual chip documentation files for automatic mode
204 pwm[1-*]_mode 0: DC mode (direct current)
205 1: PWM mode (pulse-width modulation)
208 pwm[1-*]_freq Base PWM frequency in Hz.
209 Only possibly available when pwmN_mode is PWM, but not always
213 pwm[1-*]_auto_channels_temp
214 Select which temperature channels affect this PWM output in
215 auto mode. Bitfield, 1 is temp1, 2 is temp2, 4 is temp3 etc...
216 Which values are possible depend on the chip used.
219 pwm[1-*]_auto_point[1-*]_pwm
220 pwm[1-*]_auto_point[1-*]_temp
221 pwm[1-*]_auto_point[1-*]_temp_hyst
222 Define the PWM vs temperature curve. Number of trip points is
223 chip-dependent. Use this for chips which associate trip points
224 to PWM output channels.
229 temp[1-*]_auto_point[1-*]_pwm
230 temp[1-*]_auto_point[1-*]_temp
231 temp[1-*]_auto_point[1-*]_temp_hyst
232 Define the PWM vs temperature curve. Number of trip points is
233 chip-dependent. Use this for chips which associate trip points
234 to temperature channels.
242 temp[1-*]_type Sensor type selection.
251 Not all types are supported by all chips
253 temp[1-*]_max Temperature max value.
254 Unit: millidegree Celsius (or millivolt, see below)
257 temp[1-*]_min Temperature min value.
258 Unit: millidegree Celsius
262 Temperature hysteresis value for max limit.
263 Unit: millidegree Celsius
264 Must be reported as an absolute temperature, NOT a delta
268 temp[1-*]_input Temperature input value.
269 Unit: millidegree Celsius
272 temp[1-*]_crit Temperature critical value, typically greater than
273 corresponding temp_max values.
274 Unit: millidegree Celsius
278 Temperature hysteresis value for critical limit.
279 Unit: millidegree Celsius
280 Must be reported as an absolute temperature, NOT a delta
281 from the critical value.
285 Temperature offset which is added to the temperature reading
287 Unit: millidegree Celsius
290 temp[1-*]_label Suggested temperature channel label.
292 Should only be created if the driver has hints about what
293 this temperature channel is being used for, and user-space
294 doesn't. In all other cases, the label is provided by
298 Some chips measure temperature using external thermistors and an ADC, and
299 report the temperature measurement as a voltage. Converting this voltage
300 back to a temperature (or the other way around for limits) requires
301 mathematical functions not available in the kernel, so the conversion
302 must occur in user space. For these chips, all temp* files described
303 above should contain values expressed in millivolt instead of millidegree
304 Celsius. In other words, such temperature channels are handled as voltage
305 channels by the driver.
307 Also see the Alarms section for status flags associated with temperatures.
314 Note that no known chip provides current measurements as of writing,
315 so this part is theoretical, so to say.
317 curr[1-*]_max Current max value
321 curr[1-*]_min Current min value.
325 curr[1-*]_input Current input value
333 power[1-*]_average Average power use
337 power[1-*]_average_interval Power use averaging interval
341 power[1-*]_average_highest Historical average maximum power use
345 power[1-*]_average_lowest Historical average minimum power use
349 power[1-*]_input Instantaneous power use
353 power[1-*]_input_highest Historical maximum power use
357 power[1-*]_input_lowest Historical minimum power use
361 power[1-*]_reset_history Reset input_highest, input_lowest,
362 average_highest and average_lowest.
369 energy[1-*]_input Cumulative energy use
378 Each channel or limit may have an associated alarm file, containing a
379 boolean value. 1 means than an alarm condition exists, 0 means no alarm.
381 Usually a given chip will either use channel-related alarms, or
382 limit-related alarms, not both. The driver should just reflect the hardware
407 Each input channel may have an associated fault file. This can be used
408 to notify open diodes, unconnected fans etc. where the hardware
409 supports it. When this boolean has value 1, the measurement for that
410 channel should not be trusted.
415 Input fault condition
420 Some chips also offer the possibility to get beeped when an alarm occurs:
422 beep_enable Master beep enable
435 In theory, a chip could provide per-limit beep masking, but no such chip
438 Old drivers provided a different, non-standard interface to alarms and
439 beeps. These interface files are deprecated, but will be kept around
440 for compatibility reasons:
442 alarms Alarm bitmask.
444 Integer representation of one to four bytes.
445 A '1' bit means an alarm.
446 Chips should be programmed for 'comparator' mode so that
447 the alarm will 'come back' after you read the register
448 if it is still valid.
449 Generally a direct representation of a chip's internal
450 alarm registers; there is no standard for the position
451 of individual bits. For this reason, the use of this
452 interface file for new drivers is discouraged. Use
453 individual *_alarm and *_fault files instead.
454 Bits are defined in kernel/include/sensors.h.
456 beep_mask Bitmask for beep.
457 Same format as 'alarms' with the same bit locations,
458 use discouraged for the same reason. Use individual
459 *_beep files instead.
463 ***********************
464 * Intrusion detection *
465 ***********************
468 Chassis intrusion detection
470 1: intrusion detected
472 Contrary to regular alarm flags which clear themselves
473 automatically when read, this one sticks until cleared by
474 the user. This is done by writing 0 to the file. Writing
475 other values is unsupported.
478 Chassis intrusion beep
484 sysfs attribute writes interpretation
485 -------------------------------------
487 hwmon sysfs attributes always contain numbers, so the first thing to do is to
488 convert the input to a number, there are 2 ways todo this depending whether
489 the number can be negative or not:
490 unsigned long u = simple_strtoul(buf, NULL, 10);
491 long s = simple_strtol(buf, NULL, 10);
493 With buf being the buffer with the user input being passed by the kernel.
494 Notice that we do not use the second argument of strto[u]l, and thus cannot
495 tell when 0 is returned, if this was really 0 or is caused by invalid input.
496 This is done deliberately as checking this everywhere would add a lot of
499 Notice that it is important to always store the converted value in an
500 unsigned long or long, so that no wrap around can happen before any further
503 After the input string is converted to an (unsigned) long, the value should be
504 checked if its acceptable. Be careful with further conversions on the value
505 before checking it for validity, as these conversions could still cause a wrap
506 around before the check. For example do not multiply the result, and only
507 add/subtract if it has been divided before the add/subtract.
509 What to do if a value is found to be invalid, depends on the type of the
510 sysfs attribute that is being set. If it is a continuous setting like a
511 tempX_max or inX_max attribute, then the value should be clamped to its
512 limits using SENSORS_LIMIT(value, min_limit, max_limit). If it is not
513 continuous like for example a tempX_type, then when an invalid value is
514 written, -EINVAL should be returned.
516 Example1, temp1_max, register is a signed 8 bit value (-128 - 127 degrees):
518 long v = simple_strtol(buf, NULL, 10) / 1000;
519 v = SENSORS_LIMIT(v, -128, 127);
520 /* write v to register */
522 Example2, fan divider setting, valid values 2, 4 and 8:
524 unsigned long v = simple_strtoul(buf, NULL, 10);
527 case 2: v = 1; break;
528 case 4: v = 2; break;
529 case 8: v = 3; break;
533 /* write v to register */
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