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. See libsensors documentation and source for
6 more further information. As of writing this document, libsensors
7 (from lm_sensors 2.8.3) is heavily chip-dependant. Adding or updating
8 support for any given chip requires modifying the library's code.
9 This is because libsensors was written for the procfs interface
10 older kernel modules were using, which wasn't standardized enough.
11 Recent versions of libsensors (from lm_sensors 2.8.2 and later) have
12 support for the sysfs interface, though.
14 The new sysfs interface was designed to be as chip-independant as
17 Note that motherboards vary widely in the connections to sensor chips.
18 There is no standard that ensures, for example, that the second
19 temperature sensor is connected to the CPU, or that the second fan is on
20 the CPU. Also, some values reported by the chips need some computation
21 before they make full sense. For example, most chips can only measure
22 voltages between 0 and +4V. Other voltages are scaled back into that
23 range using external resistors. Since the values of these resistors
24 can change from motherboard to motherboard, the conversions cannot be
25 hard coded into the driver and have to be done in user space.
27 For this reason, even if we aim at a chip-independant libsensors, it will
28 still require a configuration file (e.g. /etc/sensors.conf) for proper
29 values conversion, labeling of inputs and hiding of unused inputs.
31 An alternative method that some programs use is to access the sysfs
32 files directly. This document briefly describes the standards that the
33 drivers follow, so that an application program can scan for entries and
34 access this data in a simple and consistent way. That said, such programs
35 will have to implement conversion, labeling and hiding of inputs. For
36 this reason, it is still not recommended to bypass the library.
38 If you are developing a userspace application please send us feedback on
41 Note that this standard isn't completely established yet, so it is subject
42 to changes, even important ones. One more reason to use the library instead
43 of accessing sysfs files directly.
45 Each chip gets its own directory in the sysfs /sys/devices tree. To
46 find all sensor chips, it is easier to follow the symlinks from
49 All sysfs values are fixed point numbers. To get the true value of some
50 of the values, you should divide by the specified value.
52 There is only one value per file, unlike the older /proc specification.
53 The common scheme for files naming is: <type><number>_<item>. Usual
54 types for sensor chips are "in" (voltage), "temp" (temperature) and
55 "fan" (fan). Usual items are "input" (measured value), "max" (high
56 threshold, "min" (low threshold). Numbering usually starts from 1,
57 except for voltages which start from 0 (because most data sheets use
58 this). A number is always used for elements that can be present more
59 than once, even if there is a single element of the given type on the
60 specific chip. Other files do not refer to a specific element, so
61 they have a simple name, and no number.
63 Alarms are direct indications read from the chips. The drivers do NOT
64 make comparisons of readings to thresholds. This allows violations
65 between readings to be caught and alarmed. The exact definition of an
66 alarm (for example, whether a threshold must be met or must be exceeded
67 to cause an alarm) is chip-dependent.
70 -------------------------------------------------------------------------
76 in[0-8]_min Voltage min value.
80 in[0-8]_max Voltage max value.
84 in[0-8]_input Voltage input value.
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.
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)
107 in0_ref CPU core reference voltage.
112 vrm Voltage Regulator Module version number.
114 Two digit number, first is major version, second is
116 Affects the way the driver calculates the CPU core reference
117 voltage from the vid pins.
124 fan[1-3]_min Fan minimum value
125 Unit: revolution/min (RPM)
128 fan[1-3]_input Fan input value.
129 Unit: revolution/min (RPM)
132 fan[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.
138 fan[1-3]_pwm Pulse width modulation fan control.
139 Integer value in the range 0 to 255
144 Switch PWM on and off.
145 Not always present even if fan*_pwm is.
155 temp[1-3]_type Sensor type selection.
156 Integers 1, 2, 3 or thermistor Beta value (3435)
161 Not all types are supported by all chips
163 temp[1-4]_max Temperature max value.
164 Unit: millidegree Celcius
167 temp[1-3]_min Temperature min value.
168 Unit: millidegree Celcius
172 Temperature hysteresis value for max limit.
173 Unit: millidegree Celcius
174 Must be reported as an absolute temperature, NOT a delta
178 temp[1-4]_input Temperature input value.
179 Unit: millidegree Celcius
182 temp[1-4]_crit Temperature critical value, typically greater than
183 corresponding temp_max values.
184 Unit: millidegree Celcius
188 Temperature hysteresis value for critical limit.
189 Unit: millidegree Celcius
190 Must be reported as an absolute temperature, NOT a delta
191 from the critical value.
194 If there are multiple temperature sensors, temp1_* is
195 generally the sensor inside the chip itself,
196 reported as "motherboard temperature". temp2_* to
197 temp4_* are generally sensors external to the chip
198 itself, for example the thermal diode inside the CPU or
206 Note that no known chip provides current measurements as of writing,
207 so this part is theoretical, so to say.
209 curr[1-n]_max Current max value
213 curr[1-n]_min Current min value.
217 curr[1-n]_input Current input value
226 alarms Alarm bitmask.
228 Integer representation of one to four bytes.
229 A '1' bit means an alarm.
230 Chips should be programmed for 'comparator' mode so that
231 the alarm will 'come back' after you read the register
232 if it is still valid.
233 Generally a direct representation of a chip's internal
234 alarm registers; there is no standard for the position
236 Bits are defined in kernel/include/sensors.h.
238 beep_enable Beep/interrupt enable
243 beep_mask Bitmask for beep.
244 Same format as 'alarms' with the same bit locations.
247 eeprom Raw EEPROM data in binary form.