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`update_interval` 103 The interval at which the chip will update readings. 104 105 106******** 107Voltages 108******** 109 110`in[0-*]_min` 111 Voltage min value. 112 113`in[0-*]_lcrit` 114 Voltage critical min value. 115 116`in[0-*]_max` 117 Voltage max value. 118 119`in[0-*]_crit` 120 Voltage critical max value. 121 122`in[0-*]_input` 123 Voltage input value. 124 125`in[0-*]_average` 126 Average voltage 127 128`in[0-*]_lowest` 129 Historical minimum voltage 130 131`in[0-*]_highest` 132 Historical maximum voltage 133 134`in[0-*]_reset_history` 135 Reset inX_lowest and inX_highest 136 137`in_reset_history` 138 Reset inX_lowest and inX_highest for all sensors 139 140`in[0-*]_label` 141 Suggested voltage channel label. 142 143`in[0-*]_enable` 144 Enable or disable the sensors. 145 146`cpu[0-*]_vid` 147 CPU core reference voltage. 148 149`vrm` 150 Voltage Regulator Module version number. 151 152`in[0-*]_rated_min` 153 Minimum rated voltage. 154 155`in[0-*]_rated_max` 156 Maximum rated voltage. 157 158Also see the Alarms section for status flags associated with voltages. 159 160 161**** 162Fans 163**** 164 165`fan[1-*]_min` 166 Fan minimum value 167 168`fan[1-*]_max` 169 Fan maximum value 170 171`fan[1-*]_input` 172 Fan input value. 173 174`fan[1-*]_div` 175 Fan divisor. 176 177`fan[1-*]_pulses` 178 Number of tachometer pulses per fan revolution. 179 180`fan[1-*]_target` 181 Desired fan speed 182 183`fan[1-*]_label` 184 Suggested fan channel label. 185 186`fan[1-*]_enable` 187 Enable or disable the sensors. 188 189Also see the Alarms section for status flags associated with fans. 190 191 192*** 193PWM 194*** 195 196`pwm[1-*]` 197 Pulse width modulation fan control. 198 199`pwm[1-*]_enable` 200 Fan speed control method: 201 202`pwm[1-*]_mode` 203 direct current or pulse-width modulation. 204 205`pwm[1-*]_freq` 206 Base PWM frequency in Hz. 207 208`pwm[1-*]_auto_channels_temp` 209 Select which temperature channels affect this PWM output in 210 auto mode. 211 212`pwm[1-*]_auto_point[1-*]_pwm` / `pwm[1-*]_auto_point[1-*]_temp` / `pwm[1-*]_auto_point[1-*]_temp_hyst` 213 Define the PWM vs temperature curve. 214 215`temp[1-*]_auto_point[1-*]_pwm` / `temp[1-*]_auto_point[1-*]_temp` / `temp[1-*]_auto_point[1-*]_temp_hyst` 216 Define the PWM vs temperature curve. 217 218There is a third case where trip points are associated to both PWM output 219channels and temperature channels: the PWM values are associated to PWM 220output channels while the temperature values are associated to temperature 221channels. In that case, the result is determined by the mapping between 222temperature inputs and PWM outputs. When several temperature inputs are 223mapped to a given PWM output, this leads to several candidate PWM values. 224The actual result is up to the chip, but in general the highest candidate 225value (fastest fan speed) wins. 226 227 228************ 229Temperatures 230************ 231 232`temp[1-*]_type` 233 Sensor type selection. 234 235`temp[1-*]_max` 236 Temperature max value. 237 238`temp[1-*]_min` 239 Temperature min value. 240 241`temp[1-*]_max_hyst` 242 Temperature hysteresis value for max limit. 243 244`temp[1-*]_min_hyst` 245 Temperature hysteresis value for min limit. 246 247`temp[1-*]_input` 248 Temperature input value. 249 250`temp[1-*]_crit` 251 Temperature critical max value, typically greater than 252 corresponding temp_max values. 253 254`temp[1-*]_crit_hyst` 255 Temperature hysteresis value for critical limit. 256 257`temp[1-*]_emergency` 258 Temperature emergency max value, for chips supporting more than 259 two upper temperature limits. 260 261`temp[1-*]_emergency_hyst` 262 Temperature hysteresis value for emergency limit. 263 264`temp[1-*]_lcrit` 265 Temperature critical min value, typically lower than 266 corresponding temp_min values. 267 268`temp[1-*]_lcrit_hyst` 269 Temperature hysteresis value for critical min limit. 270 271`temp[1-*]_offset` 272 Temperature offset which is added to the temperature reading 273 by the chip. 274 275`temp[1-*]_label` 276 Suggested temperature channel label. 277 278`temp[1-*]_lowest` 279 Historical minimum temperature 280 281`temp[1-*]_highest` 282 Historical maximum temperature 283 284`temp[1-*]_reset_history` 285 Reset temp_lowest and temp_highest 286 287`temp_reset_history` 288 Reset temp_lowest and temp_highest for all sensors 289 290`temp[1-*]_enable` 291 Enable or disable the sensors. 292 293`temp[1-*]_rated_min` 294 Minimum rated temperature. 295 296`temp[1-*]_rated_max` 297 Maximum rated temperature. 298 299Some chips measure temperature using external thermistors and an ADC, and 300report the temperature measurement as a voltage. Converting this voltage 301back to a temperature (or the other way around for limits) requires 302mathematical functions not available in the kernel, so the conversion 303must occur in user space. For these chips, all temp* files described 304above should contain values expressed in millivolt instead of millidegree 305Celsius. In other words, such temperature channels are handled as voltage 306channels by the driver. 307 308Also see the Alarms section for status flags associated with temperatures. 309 310 311******** 312Currents 313******** 314 315`curr[1-*]_max` 316 Current max value. 317 318`curr[1-*]_min` 319 Current min value. 320 321`curr[1-*]_lcrit` 322 Current critical low value 323 324`curr[1-*]_crit` 325 Current critical high value. 326 327`curr[1-*]_input` 328 Current input value. 329 330`curr[1-*]_average` 331 Average current use. 332 333`curr[1-*]_lowest` 334 Historical minimum current. 335 336`curr[1-*]_highest` 337 Historical maximum current. 338 339`curr[1-*]_reset_history` 340 Reset currX_lowest and currX_highest 341 342 WO 343 344`curr_reset_history` 345 Reset currX_lowest and currX_highest for all sensors. 346 347`curr[1-*]_enable` 348 Enable or disable the sensors. 349 350`curr[1-*]_rated_min` 351 Minimum rated current. 352 353`curr[1-*]_rated_max` 354 Maximum rated current. 355 356Also see the Alarms section for status flags associated with currents. 357 358***** 359Power 360***** 361 362`power[1-*]_average` 363 Average power use. 364 365`power[1-*]_average_interval` 366 Power use averaging interval. 367 368`power[1-*]_average_interval_max` 369 Maximum power use averaging interval. 370 371`power[1-*]_average_interval_min` 372 Minimum power use averaging interval. 373 374`power[1-*]_average_highest` 375 Historical average maximum power use 376 377`power[1-*]_average_lowest` 378 Historical average minimum power use 379 380`power[1-*]_average_max` 381 A poll notification is sent to `power[1-*]_average` when 382 power use rises above this value. 383 384`power[1-*]_average_min` 385 A poll notification is sent to `power[1-*]_average` when 386 power use sinks below this value. 387 388`power[1-*]_input` 389 Instantaneous power use. 390 391`power[1-*]_input_highest` 392 Historical maximum power use 393 394`power[1-*]_input_lowest` 395 Historical minimum power use. 396 397`power[1-*]_reset_history` 398 Reset input_highest, input_lowest, average_highest and 399 average_lowest. 400 401`power[1-*]_accuracy` 402 Accuracy of the power meter. 403 404`power[1-*]_cap` 405 If power use rises above this limit, the 406 system should take action to reduce power use. 407 408`power[1-*]_cap_hyst` 409 Margin of hysteresis built around capping and notification. 410 411`power[1-*]_cap_max` 412 Maximum cap that can be set. 413 414`power[1-*]_cap_min` 415 Minimum cap that can be set. 416 417`power[1-*]_max` 418 Maximum power. 419 420`power[1-*]_crit` 421 Critical maximum power. 422 423 If power rises to or above this limit, the 424 system is expected take drastic action to reduce 425 power consumption, such as a system shutdown or 426 a forced powerdown of some devices. 427 428 Unit: microWatt 429 430 RW 431 432`power[1-*]_enable` 433 Enable or disable the sensors. 434 435 When disabled the sensor read will return 436 -ENODATA. 437 438 - 1: Enable 439 - 0: Disable 440 441 RW 442 443`power[1-*]_rated_min` 444 Minimum rated power. 445 446 Unit: microWatt 447 448 RO 449 450`power[1-*]_rated_max` 451 Maximum rated power. 452 453 Unit: microWatt 454 455 RO 456 457Also see the Alarms section for status flags associated with power readings. 458 459****** 460Energy 461****** 462 463`energy[1-*]_input` 464 Cumulative energy use 465 466 Unit: microJoule 467 468 RO 469 470`energy[1-*]_enable` 471 Enable or disable the sensors. 472 473 When disabled the sensor read will return 474 -ENODATA. 475 476 - 1: Enable 477 - 0: Disable 478 479 RW 480 481******** 482Humidity 483******** 484 485`humidity[1-*]_input` 486 Humidity. 487 488`humidity[1-*]_enable` 489 Enable or disable the sensors. 490 491`humidity[1-*]_rated_min` 492 Minimum rated humidity. 493 494`humidity[1-*]_rated_max` 495 Maximum rated humidity. 496 497****** 498Alarms 499****** 500 501Each channel or limit may have an associated alarm file, containing a 502boolean value. 1 means than an alarm condition exists, 0 means no alarm. 503 504Usually a given chip will either use channel-related alarms, or 505limit-related alarms, not both. The driver should just reflect the hardware 506implementation. 507 508+-------------------------------+-----------------------+ 509| **`in[0-*]_alarm`, | Channel alarm | 510| `curr[1-*]_alarm`, | | 511| `power[1-*]_alarm`, | - 0: no alarm | 512| `fan[1-*]_alarm`, | - 1: alarm | 513| `temp[1-*]_alarm`** | | 514| | RO | 515+-------------------------------+-----------------------+ 516 517**OR** 518 519+-------------------------------+-----------------------+ 520| **`in[0-*]_min_alarm`, | Limit alarm | 521| `in[0-*]_max_alarm`, | | 522| `in[0-*]_lcrit_alarm`, | - 0: no alarm | 523| `in[0-*]_crit_alarm`, | - 1: alarm | 524| `curr[1-*]_min_alarm`, | | 525| `curr[1-*]_max_alarm`, | RO | 526| `curr[1-*]_lcrit_alarm`, | | 527| `curr[1-*]_crit_alarm`, | | 528| `power[1-*]_cap_alarm`, | | 529| `power[1-*]_max_alarm`, | | 530| `power[1-*]_crit_alarm`, | | 531| `fan[1-*]_min_alarm`, | | 532| `fan[1-*]_max_alarm`, | | 533| `temp[1-*]_min_alarm`, | | 534| `temp[1-*]_max_alarm`, | | 535| `temp[1-*]_lcrit_alarm`, | | 536| `temp[1-*]_crit_alarm`, | | 537| `temp[1-*]_emergency_alarm`** | | 538+-------------------------------+-----------------------+ 539 540Each input channel may have an associated fault file. This can be used 541to notify open diodes, unconnected fans etc. where the hardware 542supports it. When this boolean has value 1, the measurement for that 543channel should not be trusted. 544 545`fan[1-*]_fault` / `temp[1-*]_fault` 546 Input fault condition. 547 548Some chips also offer the possibility to get beeped when an alarm occurs: 549 550`beep_enable` 551 Master beep enable. 552 553`in[0-*]_beep`, `curr[1-*]_beep`, `fan[1-*]_beep`, `temp[1-*]_beep`, 554 Channel beep. 555 556In theory, a chip could provide per-limit beep masking, but no such chip 557was seen so far. 558 559Old drivers provided a different, non-standard interface to alarms and 560beeps. These interface files are deprecated, but will be kept around 561for compatibility reasons: 562 563`alarms` 564 Alarm bitmask. 565 566`beep_mask` 567 Bitmask for beep. 568 569 570******************* 571Intrusion detection 572******************* 573 574`intrusion[0-*]_alarm` 575 Chassis intrusion detection. 576 577`intrusion[0-*]_beep` 578 Chassis intrusion beep. 579 580**************************** 581Average sample configuration 582**************************** 583 584Devices allowing for reading {in,power,curr,temp}_average values may export 585attributes for controlling number of samples used to compute average. 586 587+--------------+---------------------------------------------------------------+ 588| samples | Sets number of average samples for all types of measurements. | 589| | | 590| | RW | 591+--------------+---------------------------------------------------------------+ 592| in_samples | Sets number of average samples for specific type of | 593| power_samples| measurements. | 594| curr_samples | | 595| temp_samples | Note that on some devices it won't be possible to set all of | 596| | them to different values so changing one might also change | 597| | some others. | 598| | | 599| | RW | 600+--------------+---------------------------------------------------------------+ 601 602sysfs attribute writes interpretation 603------------------------------------- 604 605hwmon sysfs attributes always contain numbers, so the first thing to do is to 606convert the input to a number, there are 2 ways todo this depending whether 607the number can be negative or not:: 608 609 unsigned long u = simple_strtoul(buf, NULL, 10); 610 long s = simple_strtol(buf, NULL, 10); 611 612With buf being the buffer with the user input being passed by the kernel. 613Notice that we do not use the second argument of strto[u]l, and thus cannot 614tell when 0 is returned, if this was really 0 or is caused by invalid input. 615This is done deliberately as checking this everywhere would add a lot of 616code to the kernel. 617 618Notice that it is important to always store the converted value in an 619unsigned long or long, so that no wrap around can happen before any further 620checking. 621 622After the input string is converted to an (unsigned) long, the value should be 623checked if its acceptable. Be careful with further conversions on the value 624before checking it for validity, as these conversions could still cause a wrap 625around before the check. For example do not multiply the result, and only 626add/subtract if it has been divided before the add/subtract. 627 628What to do if a value is found to be invalid, depends on the type of the 629sysfs attribute that is being set. If it is a continuous setting like a 630tempX_max or inX_max attribute, then the value should be clamped to its 631limits using clamp_val(value, min_limit, max_limit). If it is not continuous 632like for example a tempX_type, then when an invalid value is written, 633-EINVAL should be returned. 634 635Example1, temp1_max, register is a signed 8 bit value (-128 - 127 degrees):: 636 637 long v = simple_strtol(buf, NULL, 10) / 1000; 638 v = clamp_val(v, -128, 127); 639 /* write v to register */ 640 641Example2, fan divider setting, valid values 2, 4 and 8:: 642 643 unsigned long v = simple_strtoul(buf, NULL, 10); 644 645 switch (v) { 646 case 2: v = 1; break; 647 case 4: v = 2; break; 648 case 8: v = 3; break; 649 default: 650 return -EINVAL; 651 } 652 /* write v to register */ 653