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. Since lm-sensors 3.0.0, libsensors is 6completely chip-independent. It assumes that all the kernel drivers 7implement the standard sysfs interface described in this document. 8This makes adding or updating support for any given chip very easy, as 9libsensors, and applications using it, do not need to be modified. 10This is a major improvement compared to lm-sensors 2. 11 12Note that motherboards vary widely in the connections to sensor chips. 13There is no standard that ensures, for example, that the second 14temperature sensor is connected to the CPU, or that the second fan is on 15the CPU. Also, some values reported by the chips need some computation 16before they make full sense. For example, most chips can only measure 17voltages between 0 and +4V. Other voltages are scaled back into that 18range using external resistors. Since the values of these resistors 19can change from motherboard to motherboard, the conversions cannot be 20hard coded into the driver and have to be done in user space. 21 22For this reason, even if we aim at a chip-independent libsensors, it will 23still require a configuration file (e.g. /etc/sensors.conf) for proper 24values conversion, labeling of inputs and hiding of unused inputs. 25 26An alternative method that some programs use is to access the sysfs 27files directly. This document briefly describes the standards that the 28drivers follow, so that an application program can scan for entries and 29access this data in a simple and consistent way. That said, such programs 30will have to implement conversion, labeling and hiding of inputs. For 31this reason, it is still not recommended to bypass the library. 32 33Each chip gets its own directory in the sysfs /sys/devices tree. To 34find all sensor chips, it is easier to follow the device symlinks from 35`/sys/class/hwmon/hwmon*`. 36 37Up to lm-sensors 3.0.0, libsensors looks for hardware monitoring attributes 38in the "physical" device directory. Since lm-sensors 3.0.1, attributes found 39in the hwmon "class" device directory are also supported. Complex drivers 40(e.g. drivers for multifunction chips) may want to use this possibility to 41avoid namespace pollution. The only drawback will be that older versions of 42libsensors won't support the driver in question. 43 44All sysfs values are fixed point numbers. 45 46There is only one value per file, unlike the older /proc specification. 47The common scheme for files naming is: <type><number>_<item>. Usual 48types for sensor chips are "in" (voltage), "temp" (temperature) and 49"fan" (fan). Usual items are "input" (measured value), "max" (high 50threshold, "min" (low threshold). Numbering usually starts from 1, 51except for voltages which start from 0 (because most data sheets use 52this). A number is always used for elements that can be present more 53than once, even if there is a single element of the given type on the 54specific chip. Other files do not refer to a specific element, so 55they have a simple name, and no number. 56 57Alarms are direct indications read from the chips. The drivers do NOT 58make comparisons of readings to thresholds. This allows violations 59between readings to be caught and alarmed. The exact definition of an 60alarm (for example, whether a threshold must be met or must be exceeded 61to cause an alarm) is chip-dependent. 62 63When setting values of hwmon sysfs attributes, the string representation of 64the desired value must be written, note that strings which are not a number 65are 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. 67 68Attribute access 69---------------- 70 71Hardware monitoring sysfs attributes are displayed by unrestricted userspace 72applications. For this reason, all standard ABI attributes shall be world 73readable. Writeable standard ABI attributes shall be writeable only for 74privileged users. 75 76------------------------------------------------------------------------- 77 78======= =========================================== 79`[0-*]` denotes any positive number starting from 0 80`[1-*]` denotes any positive number starting from 1 81RO read only value 82WO write only value 83RW read/write value 84======= =========================================== 85 86Read/write values may be read-only for some chips, depending on the 87hardware implementation. 88 89All entries (except name) are optional, and should only be created in a 90given driver if the chip has the feature. 91 92See Documentation/ABI/testing/sysfs-class-hwmon for a complete description 93of the attributes. 94 95***************** 96Global attributes 97***************** 98 99`name` 100 The chip name. 101 102`label` 103 A descriptive label that allows to uniquely identify a device 104 within the system. 105 106`update_interval` 107 The interval at which the chip will update readings. 108 109 110******** 111Voltages 112******** 113 114`in[0-*]_min` 115 Voltage min value. 116 117`in[0-*]_lcrit` 118 Voltage critical min value. 119 120`in[0-*]_max` 121 Voltage max value. 122 123`in[0-*]_crit` 124 Voltage critical max value. 125 126`in[0-*]_input` 127 Voltage input value. 128 129`in[0-*]_average` 130 Average voltage 131 132`in[0-*]_lowest` 133 Historical minimum voltage 134 135`in[0-*]_highest` 136 Historical maximum voltage 137 138`in[0-*]_reset_history` 139 Reset inX_lowest and inX_highest 140 141`in_reset_history` 142 Reset inX_lowest and inX_highest for all sensors 143 144`in[0-*]_label` 145 Suggested voltage channel label. 146 147`in[0-*]_enable` 148 Enable or disable the sensors. 149 150`cpu[0-*]_vid` 151 CPU core reference voltage. 152 153`vrm` 154 Voltage Regulator Module version number. 155 156`in[0-*]_rated_min` 157 Minimum rated voltage. 158 159`in[0-*]_rated_max` 160 Maximum rated voltage. 161 162Also see the Alarms section for status flags associated with voltages. 163 164 165**** 166Fans 167**** 168 169`fan[1-*]_min` 170 Fan minimum value 171 172`fan[1-*]_max` 173 Fan maximum value 174 175`fan[1-*]_input` 176 Fan input value. 177 178`fan[1-*]_div` 179 Fan divisor. 180 181`fan[1-*]_pulses` 182 Number of tachometer pulses per fan revolution. 183 184`fan[1-*]_target` 185 Desired fan speed 186 187`fan[1-*]_label` 188 Suggested fan channel label. 189 190`fan[1-*]_enable` 191 Enable or disable the sensors. 192 193Also see the Alarms section for status flags associated with fans. 194 195 196*** 197PWM 198*** 199 200`pwm[1-*]` 201 Pulse width modulation fan control. 202 203`pwm[1-*]_enable` 204 Fan speed control method: 205 206`pwm[1-*]_mode` 207 direct current or pulse-width modulation. 208 209`pwm[1-*]_freq` 210 Base PWM frequency in Hz. 211 212`pwm[1-*]_auto_channels_temp` 213 Select which temperature channels affect this PWM output in 214 auto mode. 215 216`pwm[1-*]_auto_point[1-*]_pwm` / `pwm[1-*]_auto_point[1-*]_temp` / `pwm[1-*]_auto_point[1-*]_temp_hyst` 217 Define the PWM vs temperature curve. 218 219`temp[1-*]_auto_point[1-*]_pwm` / `temp[1-*]_auto_point[1-*]_temp` / `temp[1-*]_auto_point[1-*]_temp_hyst` 220 Define the PWM vs temperature curve. 221 222There is a third case where trip points are associated to both PWM output 223channels and temperature channels: the PWM values are associated to PWM 224output channels while the temperature values are associated to temperature 225channels. In that case, the result is determined by the mapping between 226temperature inputs and PWM outputs. When several temperature inputs are 227mapped to a given PWM output, this leads to several candidate PWM values. 228The actual result is up to the chip, but in general the highest candidate 229value (fastest fan speed) wins. 230 231 232************ 233Temperatures 234************ 235 236`temp[1-*]_type` 237 Sensor type selection. 238 239`temp[1-*]_max` 240 Temperature max value. 241 242`temp[1-*]_min` 243 Temperature min value. 244 245`temp[1-*]_max_hyst` 246 Temperature hysteresis value for max limit. 247 248`temp[1-*]_min_hyst` 249 Temperature hysteresis value for min limit. 250 251`temp[1-*]_input` 252 Temperature input value. 253 254`temp[1-*]_crit` 255 Temperature critical max value, typically greater than 256 corresponding temp_max values. 257 258`temp[1-*]_crit_hyst` 259 Temperature hysteresis value for critical limit. 260 261`temp[1-*]_emergency` 262 Temperature emergency max value, for chips supporting more than 263 two upper temperature limits. 264 265`temp[1-*]_emergency_hyst` 266 Temperature hysteresis value for emergency limit. 267 268`temp[1-*]_lcrit` 269 Temperature critical min value, typically lower than 270 corresponding temp_min values. 271 272`temp[1-*]_lcrit_hyst` 273 Temperature hysteresis value for critical min limit. 274 275`temp[1-*]_offset` 276 Temperature offset which is added to the temperature reading 277 by the chip. 278 279`temp[1-*]_label` 280 Suggested temperature channel label. 281 282`temp[1-*]_lowest` 283 Historical minimum temperature 284 285`temp[1-*]_highest` 286 Historical maximum temperature 287 288`temp[1-*]_reset_history` 289 Reset temp_lowest and temp_highest 290 291`temp_reset_history` 292 Reset temp_lowest and temp_highest for all sensors 293 294`temp[1-*]_enable` 295 Enable or disable the sensors. 296 297`temp[1-*]_rated_min` 298 Minimum rated temperature. 299 300`temp[1-*]_rated_max` 301 Maximum rated temperature. 302 303Some chips measure temperature using external thermistors and an ADC, and 304report the temperature measurement as a voltage. Converting this voltage 305back to a temperature (or the other way around for limits) requires 306mathematical functions not available in the kernel, so the conversion 307must occur in user space. For these chips, all temp* files described 308above should contain values expressed in millivolt instead of millidegree 309Celsius. In other words, such temperature channels are handled as voltage 310channels by the driver. 311 312Also see the Alarms section for status flags associated with temperatures. 313 314 315******** 316Currents 317******** 318 319`curr[1-*]_max` 320 Current max value. 321 322`curr[1-*]_min` 323 Current min value. 324 325`curr[1-*]_lcrit` 326 Current critical low value 327 328`curr[1-*]_crit` 329 Current critical high value. 330 331`curr[1-*]_input` 332 Current input value. 333 334`curr[1-*]_average` 335 Average current use. 336 337`curr[1-*]_lowest` 338 Historical minimum current. 339 340`curr[1-*]_highest` 341 Historical maximum current. 342 343`curr[1-*]_reset_history` 344 Reset currX_lowest and currX_highest 345 346 WO 347 348`curr_reset_history` 349 Reset currX_lowest and currX_highest for all sensors. 350 351`curr[1-*]_enable` 352 Enable or disable the sensors. 353 354`curr[1-*]_rated_min` 355 Minimum rated current. 356 357`curr[1-*]_rated_max` 358 Maximum rated current. 359 360Also see the Alarms section for status flags associated with currents. 361 362***** 363Power 364***** 365 366`power[1-*]_average` 367 Average power use. 368 369`power[1-*]_average_interval` 370 Power use averaging interval. 371 372`power[1-*]_average_interval_max` 373 Maximum power use averaging interval. 374 375`power[1-*]_average_interval_min` 376 Minimum power use averaging interval. 377 378`power[1-*]_average_highest` 379 Historical average maximum power use 380 381`power[1-*]_average_lowest` 382 Historical average minimum power use 383 384`power[1-*]_average_max` 385 A poll notification is sent to `power[1-*]_average` when 386 power use rises above this value. 387 388`power[1-*]_average_min` 389 A poll notification is sent to `power[1-*]_average` when 390 power use sinks below this value. 391 392`power[1-*]_input` 393 Instantaneous power use. 394 395`power[1-*]_input_highest` 396 Historical maximum power use 397 398`power[1-*]_input_lowest` 399 Historical minimum power use. 400 401`power[1-*]_reset_history` 402 Reset input_highest, input_lowest, average_highest and 403 average_lowest. 404 405`power[1-*]_accuracy` 406 Accuracy of the power meter. 407 408`power[1-*]_cap` 409 If power use rises above this limit, the 410 system should take action to reduce power use. 411 412`power[1-*]_cap_hyst` 413 Margin of hysteresis built around capping and notification. 414 415`power[1-*]_cap_max` 416 Maximum cap that can be set. 417 418`power[1-*]_cap_min` 419 Minimum cap that can be set. 420 421`power[1-*]_max` 422 Maximum power. 423 424`power[1-*]_crit` 425 Critical maximum power. 426 427 If power rises to or above this limit, the 428 system is expected take drastic action to reduce 429 power consumption, such as a system shutdown or 430 a forced powerdown of some devices. 431 432 Unit: microWatt 433 434 RW 435 436`power[1-*]_enable` 437 Enable or disable the sensors. 438 439 When disabled the sensor read will return 440 -ENODATA. 441 442 - 1: Enable 443 - 0: Disable 444 445 RW 446 447`power[1-*]_rated_min` 448 Minimum rated power. 449 450 Unit: microWatt 451 452 RO 453 454`power[1-*]_rated_max` 455 Maximum rated power. 456 457 Unit: microWatt 458 459 RO 460 461Also see the Alarms section for status flags associated with power readings. 462 463****** 464Energy 465****** 466 467`energy[1-*]_input` 468 Cumulative energy use 469 470 Unit: microJoule 471 472 RO 473 474`energy[1-*]_enable` 475 Enable or disable the sensors. 476 477 When disabled the sensor read will return 478 -ENODATA. 479 480 - 1: Enable 481 - 0: Disable 482 483 RW 484 485******** 486Humidity 487******** 488 489`humidity[1-*]_input` 490 Humidity. 491 492`humidity[1-*]_enable` 493 Enable or disable the sensors. 494 495`humidity[1-*]_rated_min` 496 Minimum rated humidity. 497 498`humidity[1-*]_rated_max` 499 Maximum rated humidity. 500 501****** 502Alarms 503****** 504 505Each channel or limit may have an associated alarm file, containing a 506boolean value. 1 means than an alarm condition exists, 0 means no alarm. 507 508Usually a given chip will either use channel-related alarms, or 509limit-related alarms, not both. The driver should just reflect the hardware 510implementation. 511 512+-------------------------------+-----------------------+ 513| **`in[0-*]_alarm`, | Channel alarm | 514| `curr[1-*]_alarm`, | | 515| `power[1-*]_alarm`, | - 0: no alarm | 516| `fan[1-*]_alarm`, | - 1: alarm | 517| `temp[1-*]_alarm`** | | 518| | RO | 519+-------------------------------+-----------------------+ 520 521**OR** 522 523+-------------------------------+-----------------------+ 524| **`in[0-*]_min_alarm`, | Limit alarm | 525| `in[0-*]_max_alarm`, | | 526| `in[0-*]_lcrit_alarm`, | - 0: no alarm | 527| `in[0-*]_crit_alarm`, | - 1: alarm | 528| `curr[1-*]_min_alarm`, | | 529| `curr[1-*]_max_alarm`, | RO | 530| `curr[1-*]_lcrit_alarm`, | | 531| `curr[1-*]_crit_alarm`, | | 532| `power[1-*]_cap_alarm`, | | 533| `power[1-*]_max_alarm`, | | 534| `power[1-*]_crit_alarm`, | | 535| `fan[1-*]_min_alarm`, | | 536| `fan[1-*]_max_alarm`, | | 537| `temp[1-*]_min_alarm`, | | 538| `temp[1-*]_max_alarm`, | | 539| `temp[1-*]_lcrit_alarm`, | | 540| `temp[1-*]_crit_alarm`, | | 541| `temp[1-*]_emergency_alarm`** | | 542+-------------------------------+-----------------------+ 543 544Each input channel may have an associated fault file. This can be used 545to notify open diodes, unconnected fans etc. where the hardware 546supports it. When this boolean has value 1, the measurement for that 547channel should not be trusted. 548 549`fan[1-*]_fault` / `temp[1-*]_fault` 550 Input fault condition. 551 552Some chips also offer the possibility to get beeped when an alarm occurs: 553 554`beep_enable` 555 Master beep enable. 556 557`in[0-*]_beep`, `curr[1-*]_beep`, `fan[1-*]_beep`, `temp[1-*]_beep`, 558 Channel beep. 559 560In theory, a chip could provide per-limit beep masking, but no such chip 561was seen so far. 562 563Old drivers provided a different, non-standard interface to alarms and 564beeps. These interface files are deprecated, but will be kept around 565for compatibility reasons: 566 567`alarms` 568 Alarm bitmask. 569 570`beep_mask` 571 Bitmask for beep. 572 573 574******************* 575Intrusion detection 576******************* 577 578`intrusion[0-*]_alarm` 579 Chassis intrusion detection. 580 581`intrusion[0-*]_beep` 582 Chassis intrusion beep. 583 584**************************** 585Average sample configuration 586**************************** 587 588Devices allowing for reading {in,power,curr,temp}_average values may export 589attributes for controlling number of samples used to compute average. 590 591+--------------+---------------------------------------------------------------+ 592| samples | Sets number of average samples for all types of measurements. | 593| | | 594| | RW | 595+--------------+---------------------------------------------------------------+ 596| in_samples | Sets number of average samples for specific type of | 597| power_samples| measurements. | 598| curr_samples | | 599| temp_samples | Note that on some devices it won't be possible to set all of | 600| | them to different values so changing one might also change | 601| | some others. | 602| | | 603| | RW | 604+--------------+---------------------------------------------------------------+ 605 606sysfs attribute writes interpretation 607------------------------------------- 608 609hwmon sysfs attributes always contain numbers, so the first thing to do is to 610convert the input to a number, there are 2 ways todo this depending whether 611the number can be negative or not:: 612 613 unsigned long u = simple_strtoul(buf, NULL, 10); 614 long s = simple_strtol(buf, NULL, 10); 615 616With buf being the buffer with the user input being passed by the kernel. 617Notice that we do not use the second argument of strto[u]l, and thus cannot 618tell when 0 is returned, if this was really 0 or is caused by invalid input. 619This is done deliberately as checking this everywhere would add a lot of 620code to the kernel. 621 622Notice that it is important to always store the converted value in an 623unsigned long or long, so that no wrap around can happen before any further 624checking. 625 626After the input string is converted to an (unsigned) long, the value should be 627checked if its acceptable. Be careful with further conversions on the value 628before checking it for validity, as these conversions could still cause a wrap 629around before the check. For example do not multiply the result, and only 630add/subtract if it has been divided before the add/subtract. 631 632What to do if a value is found to be invalid, depends on the type of the 633sysfs attribute that is being set. If it is a continuous setting like a 634tempX_max or inX_max attribute, then the value should be clamped to its 635limits using clamp_val(value, min_limit, max_limit). If it is not continuous 636like for example a tempX_type, then when an invalid value is written, 637-EINVAL should be returned. 638 639Example1, temp1_max, register is a signed 8 bit value (-128 - 127 degrees):: 640 641 long v = simple_strtol(buf, NULL, 10) / 1000; 642 v = clamp_val(v, -128, 127); 643 /* write v to register */ 644 645Example2, fan divider setting, valid values 2, 4 and 8:: 646 647 unsigned long v = simple_strtoul(buf, NULL, 10); 648 649 switch (v) { 650 case 2: v = 1; break; 651 case 4: v = 2; break; 652 case 8: v = 3; break; 653 default: 654 return -EINVAL; 655 } 656 /* write v to register */ 657