tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
1Naming and data format standards for sysfs files
2------------------------------------------------
3
4The libsensors library offers an interface to the raw sensors data
5through the sysfs interface. See libsensors documentation and source for
6more further information. As of writing this document, libsensors
7(from lm_sensors 2.8.3) is heavily chip-dependant. Adding or updating
8support for any given chip requires modifying the library's code.
9This is because libsensors was written for the procfs interface
10older kernel modules were using, which wasn't standardized enough.
11Recent versions of libsensors (from lm_sensors 2.8.2 and later) have
12support for the sysfs interface, though.
13
14The new sysfs interface was designed to be as chip-independant as
15possible.
16
17Note that motherboards vary widely in the connections to sensor chips.
18There is no standard that ensures, for example, that the second
19temperature sensor is connected to the CPU, or that the second fan is on
20the CPU. Also, some values reported by the chips need some computation
21before they make full sense. For example, most chips can only measure
22voltages between 0 and +4V. Other voltages are scaled back into that
23range using external resistors. Since the values of these resistors
24can change from motherboard to motherboard, the conversions cannot be
25hard coded into the driver and have to be done in user space.
26
27For this reason, even if we aim at a chip-independant libsensors, it will
28still require a configuration file (e.g. /etc/sensors.conf) for proper
29values conversion, labeling of inputs and hiding of unused inputs.
30
31An alternative method that some programs use is to access the sysfs
32files directly. This document briefly describes the standards that the
33drivers follow, so that an application program can scan for entries and
34access this data in a simple and consistent way. That said, such programs
35will have to implement conversion, labeling and hiding of inputs. For
36this reason, it is still not recommended to bypass the library.
37
38If you are developing a userspace application please send us feedback on
39this standard.
40
41Note that this standard isn't completely established yet, so it is subject
42to changes, even important ones. One more reason to use the library instead
43of accessing sysfs files directly.
44
45Each chip gets its own directory in the sysfs /sys/devices tree. To
46find all sensor chips, it is easier to follow the symlinks from
47/sys/i2c/devices/
48
49All sysfs values are fixed point numbers. To get the true value of some
50of the values, you should divide by the specified value.
51
52There is only one value per file, unlike the older /proc specification.
53The common scheme for files naming is: <type><number>_<item>. Usual
54types for sensor chips are "in" (voltage), "temp" (temperature) and
55"fan" (fan). Usual items are "input" (measured value), "max" (high
56threshold, "min" (low threshold). Numbering usually starts from 1,
57except for voltages which start from 0 (because most data sheets use
58this). A number is always used for elements that can be present more
59than once, even if there is a single element of the given type on the
60specific chip. Other files do not refer to a specific element, so
61they have a simple name, and no number.
62
63Alarms are direct indications read from the chips. The drivers do NOT
64make comparisons of readings to thresholds. This allows violations
65between readings to be caught and alarmed. The exact definition of an
66alarm (for example, whether a threshold must be met or must be exceeded
67to cause an alarm) is chip-dependent.
68
69
70-------------------------------------------------------------------------
71
72************
73* Voltages *
74************
75
76in[0-8]_min Voltage min value.
77 Unit: millivolt
78 Read/Write
79
80in[0-8]_max Voltage max value.
81 Unit: millivolt
82 Read/Write
83
84in[0-8]_input Voltage input value.
85 Unit: millivolt
86 Read only
87 Actual voltage depends on the scaling resistors on the
88 motherboard, as recommended in the chip datasheet.
89 This varies by chip and by motherboard.
90 Because of this variation, values are generally NOT scaled
91 by the chip driver, and must be done by the application.
92 However, some drivers (notably lm87 and via686a)
93 do scale, with various degrees of success.
94 These drivers will output the actual voltage.
95
96 Typical usage:
97 in0_* CPU #1 voltage (not scaled)
98 in1_* CPU #2 voltage (not scaled)
99 in2_* 3.3V nominal (not scaled)
100 in3_* 5.0V nominal (scaled)
101 in4_* 12.0V nominal (scaled)
102 in5_* -12.0V nominal (scaled)
103 in6_* -5.0V nominal (scaled)
104 in7_* varies
105 in8_* varies
106
107cpu[0-1]_vid CPU core reference voltage.
108 Unit: millivolt
109 Read only.
110 Not always correct.
111
112vrm Voltage Regulator Module version number.
113 Read only.
114 Two digit number, first is major version, second is
115 minor version.
116 Affects the way the driver calculates the CPU core reference
117 voltage from the vid pins.
118
119
120********
121* Fans *
122********
123
124fan[1-3]_min Fan minimum value
125 Unit: revolution/min (RPM)
126 Read/Write.
127
128fan[1-3]_input Fan input value.
129 Unit: revolution/min (RPM)
130 Read only.
131
132fan[1-3]_div Fan divisor.
133 Integer value in powers of two (1, 2, 4, 8, 16, 32, 64, 128).
134 Some chips only support values 1, 2, 4 and 8.
135 Note that this is actually an internal clock divisor, which
136 affects the measurable speed range, not the read value.
137
138*******
139* PWM *
140*******
141
142pwm[1-3] Pulse width modulation fan control.
143 Integer value in the range 0 to 255
144 Read/Write
145 255 is max or 100%.
146
147pwm[1-3]_enable
148 Switch PWM on and off.
149 Not always present even if fan*_pwm is.
150 0 to turn off
151 1 to turn on in manual mode
152 2 to turn on in automatic mode
153 Read/Write
154
155pwm[1-*]_auto_channels_temp
156 Select which temperature channels affect this PWM output in
157 auto mode. Bitfield, 1 is temp1, 2 is temp2, 4 is temp3 etc...
158 Which values are possible depend on the chip used.
159
160pwm[1-*]_auto_point[1-*]_pwm
161pwm[1-*]_auto_point[1-*]_temp
162pwm[1-*]_auto_point[1-*]_temp_hyst
163 Define the PWM vs temperature curve. Number of trip points is
164 chip-dependent. Use this for chips which associate trip points
165 to PWM output channels.
166
167OR
168
169temp[1-*]_auto_point[1-*]_pwm
170temp[1-*]_auto_point[1-*]_temp
171temp[1-*]_auto_point[1-*]_temp_hyst
172 Define the PWM vs temperature curve. Number of trip points is
173 chip-dependent. Use this for chips which associate trip points
174 to temperature channels.
175
176
177****************
178* Temperatures *
179****************
180
181temp[1-3]_type Sensor type selection.
182 Integers 1 to 4 or thermistor Beta value (typically 3435)
183 Read/Write.
184 1: PII/Celeron Diode
185 2: 3904 transistor
186 3: thermal diode
187 4: thermistor (default/unknown Beta)
188 Not all types are supported by all chips
189
190temp[1-4]_max Temperature max value.
191 Unit: millidegree Celcius
192 Read/Write value.
193
194temp[1-3]_min Temperature min value.
195 Unit: millidegree Celcius
196 Read/Write value.
197
198temp[1-3]_max_hyst
199 Temperature hysteresis value for max limit.
200 Unit: millidegree Celcius
201 Must be reported as an absolute temperature, NOT a delta
202 from the max value.
203 Read/Write value.
204
205temp[1-4]_input Temperature input value.
206 Unit: millidegree Celcius
207 Read only value.
208
209temp[1-4]_crit Temperature critical value, typically greater than
210 corresponding temp_max values.
211 Unit: millidegree Celcius
212 Read/Write value.
213
214temp[1-2]_crit_hyst
215 Temperature hysteresis value for critical limit.
216 Unit: millidegree Celcius
217 Must be reported as an absolute temperature, NOT a delta
218 from the critical value.
219 Read/Write value.
220
221 If there are multiple temperature sensors, temp1_* is
222 generally the sensor inside the chip itself,
223 reported as "motherboard temperature". temp2_* to
224 temp4_* are generally sensors external to the chip
225 itself, for example the thermal diode inside the CPU or
226 a thermistor nearby.
227
228
229************
230* Currents *
231************
232
233Note that no known chip provides current measurements as of writing,
234so this part is theoretical, so to say.
235
236curr[1-n]_max Current max value
237 Unit: milliampere
238 Read/Write.
239
240curr[1-n]_min Current min value.
241 Unit: milliampere
242 Read/Write.
243
244curr[1-n]_input Current input value
245 Unit: milliampere
246 Read only.
247
248
249*********
250* Other *
251*********
252
253alarms Alarm bitmask.
254 Read only.
255 Integer representation of one to four bytes.
256 A '1' bit means an alarm.
257 Chips should be programmed for 'comparator' mode so that
258 the alarm will 'come back' after you read the register
259 if it is still valid.
260 Generally a direct representation of a chip's internal
261 alarm registers; there is no standard for the position
262 of individual bits.
263 Bits are defined in kernel/include/sensors.h.
264
265alarms_in Alarm bitmask relative to in (voltage) channels
266 Read only
267 A '1' bit means an alarm, LSB corresponds to in0 and so on
268 Prefered to 'alarms' for newer chips
269
270alarms_fan Alarm bitmask relative to fan channels
271 Read only
272 A '1' bit means an alarm, LSB corresponds to fan1 and so on
273 Prefered to 'alarms' for newer chips
274
275alarms_temp Alarm bitmask relative to temp (temperature) channels
276 Read only
277 A '1' bit means an alarm, LSB corresponds to temp1 and so on
278 Prefered to 'alarms' for newer chips
279
280beep_enable Beep/interrupt enable
281 0 to disable.
282 1 to enable.
283 Read/Write
284
285beep_mask Bitmask for beep.
286 Same format as 'alarms' with the same bit locations.
287 Read/Write
288
289eeprom Raw EEPROM data in binary form.
290 Read only.
291
292pec Enable or disable PEC (SMBus only)
293 Read/Write