Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.
1 Naming and data format standards for sysfs files 2 ------------------------------------------------ 3 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. 11 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. 21 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. 25 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. 32 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*. 36 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. 43 44 All sysfs values are fixed point numbers. 45 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. 56 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. 62 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. 67 68 ------------------------------------------------------------------------- 69 70 [0-*] denotes any positive number starting from 0 71 [1-*] denotes any positive number starting from 1 72 RO read only value 73 WO write only value 74 RW read/write value 75 76 Read/write values may be read-only for some chips, depending on the 77 hardware implementation. 78 79 All entries (except name) are optional, and should only be created in a 80 given driver if the chip has the feature. 81 82 83 ********************* 84 * Global attributes * 85 ********************* 86 87 name The chip name. 88 This should be a short, lowercase string, not containing 89 whitespace, dashes, or the wildcard character '*'. 90 This attribute represents the chip name. It is the only 91 mandatory attribute. 92 I2C devices get this attribute created automatically. 93 RO 94 95 update_interval The interval at which the chip will update readings. 96 Unit: millisecond 97 RW 98 Some devices have a variable update rate or interval. 99 This attribute can be used to change it to the desired value. 100 101 102 ************ 103 * Voltages * 104 ************ 105 106 in[0-*]_min Voltage min value. 107 Unit: millivolt 108 RW 109 110 in[0-*]_lcrit Voltage critical min value. 111 Unit: millivolt 112 RW 113 If voltage drops to or below this limit, the system may 114 take drastic action such as power down or reset. At the very 115 least, it should report a fault. 116 117 in[0-*]_max Voltage max value. 118 Unit: millivolt 119 RW 120 121 in[0-*]_crit Voltage critical max value. 122 Unit: millivolt 123 RW 124 If voltage reaches or exceeds this limit, the system may 125 take drastic action such as power down or reset. At the very 126 least, it should report a fault. 127 128 in[0-*]_input Voltage input value. 129 Unit: millivolt 130 RO 131 Voltage measured on the chip pin. 132 Actual voltage depends on the scaling resistors on the 133 motherboard, as recommended in the chip datasheet. 134 This varies by chip and by motherboard. 135 Because of this variation, values are generally NOT scaled 136 by the chip driver, and must be done by the application. 137 However, some drivers (notably lm87 and via686a) 138 do scale, because of internal resistors built into a chip. 139 These drivers will output the actual voltage. Rule of 140 thumb: drivers should report the voltage values at the 141 "pins" of the chip. 142 143 in[0-*]_average 144 Average voltage 145 Unit: millivolt 146 RO 147 148 in[0-*]_lowest 149 Historical minimum voltage 150 Unit: millivolt 151 RO 152 153 in[0-*]_highest 154 Historical maximum voltage 155 Unit: millivolt 156 RO 157 158 in[0-*]_reset_history 159 Reset inX_lowest and inX_highest 160 WO 161 162 in_reset_history 163 Reset inX_lowest and inX_highest for all sensors 164 WO 165 166 in[0-*]_label Suggested voltage channel label. 167 Text string 168 Should only be created if the driver has hints about what 169 this voltage channel is being used for, and user-space 170 doesn't. In all other cases, the label is provided by 171 user-space. 172 RO 173 174 cpu[0-*]_vid CPU core reference voltage. 175 Unit: millivolt 176 RO 177 Not always correct. 178 179 vrm Voltage Regulator Module version number. 180 RW (but changing it should no more be necessary) 181 Originally the VRM standard version multiplied by 10, but now 182 an arbitrary number, as not all standards have a version 183 number. 184 Affects the way the driver calculates the CPU core reference 185 voltage from the vid pins. 186 187 Also see the Alarms section for status flags associated with voltages. 188 189 190 ******** 191 * Fans * 192 ******** 193 194 fan[1-*]_min Fan minimum value 195 Unit: revolution/min (RPM) 196 RW 197 198 fan[1-*]_max Fan maximum value 199 Unit: revolution/min (RPM) 200 Only rarely supported by the hardware. 201 RW 202 203 fan[1-*]_input Fan input value. 204 Unit: revolution/min (RPM) 205 RO 206 207 fan[1-*]_div Fan divisor. 208 Integer value in powers of two (1, 2, 4, 8, 16, 32, 64, 128). 209 RW 210 Some chips only support values 1, 2, 4 and 8. 211 Note that this is actually an internal clock divisor, which 212 affects the measurable speed range, not the read value. 213 214 fan[1-*]_pulses Number of tachometer pulses per fan revolution. 215 Integer value, typically between 1 and 4. 216 RW 217 This value is a characteristic of the fan connected to the 218 device's input, so it has to be set in accordance with the fan 219 model. 220 Should only be created if the chip has a register to configure 221 the number of pulses. In the absence of such a register (and 222 thus attribute) the value assumed by all devices is 2 pulses 223 per fan revolution. 224 225 fan[1-*]_target 226 Desired fan speed 227 Unit: revolution/min (RPM) 228 RW 229 Only makes sense if the chip supports closed-loop fan speed 230 control based on the measured fan speed. 231 232 fan[1-*]_label Suggested fan channel label. 233 Text string 234 Should only be created if the driver has hints about what 235 this fan channel is being used for, and user-space doesn't. 236 In all other cases, the label is provided by user-space. 237 RO 238 239 Also see the Alarms section for status flags associated with fans. 240 241 242 ******* 243 * PWM * 244 ******* 245 246 pwm[1-*] Pulse width modulation fan control. 247 Integer value in the range 0 to 255 248 RW 249 255 is max or 100%. 250 251 pwm[1-*]_enable 252 Fan speed control method: 253 0: no fan speed control (i.e. fan at full speed) 254 1: manual fan speed control enabled (using pwm[1-*]) 255 2+: automatic fan speed control enabled 256 Check individual chip documentation files for automatic mode 257 details. 258 RW 259 260 pwm[1-*]_mode 0: DC mode (direct current) 261 1: PWM mode (pulse-width modulation) 262 RW 263 264 pwm[1-*]_freq Base PWM frequency in Hz. 265 Only possibly available when pwmN_mode is PWM, but not always 266 present even then. 267 RW 268 269 pwm[1-*]_auto_channels_temp 270 Select which temperature channels affect this PWM output in 271 auto mode. Bitfield, 1 is temp1, 2 is temp2, 4 is temp3 etc... 272 Which values are possible depend on the chip used. 273 RW 274 275 pwm[1-*]_auto_point[1-*]_pwm 276 pwm[1-*]_auto_point[1-*]_temp 277 pwm[1-*]_auto_point[1-*]_temp_hyst 278 Define the PWM vs temperature curve. Number of trip points is 279 chip-dependent. Use this for chips which associate trip points 280 to PWM output channels. 281 RW 282 283 temp[1-*]_auto_point[1-*]_pwm 284 temp[1-*]_auto_point[1-*]_temp 285 temp[1-*]_auto_point[1-*]_temp_hyst 286 Define the PWM vs temperature curve. Number of trip points is 287 chip-dependent. Use this for chips which associate trip points 288 to temperature channels. 289 RW 290 291 There is a third case where trip points are associated to both PWM output 292 channels and temperature channels: the PWM values are associated to PWM 293 output channels while the temperature values are associated to temperature 294 channels. In that case, the result is determined by the mapping between 295 temperature inputs and PWM outputs. When several temperature inputs are 296 mapped to a given PWM output, this leads to several candidate PWM values. 297 The actual result is up to the chip, but in general the highest candidate 298 value (fastest fan speed) wins. 299 300 301 **************** 302 * Temperatures * 303 **************** 304 305 temp[1-*]_type Sensor type selection. 306 Integers 1 to 6 307 RW 308 1: CPU embedded diode 309 2: 3904 transistor 310 3: thermal diode 311 4: thermistor 312 5: AMD AMDSI 313 6: Intel PECI 314 Not all types are supported by all chips 315 316 temp[1-*]_max Temperature max value. 317 Unit: millidegree Celsius (or millivolt, see below) 318 RW 319 320 temp[1-*]_min Temperature min value. 321 Unit: millidegree Celsius 322 RW 323 324 temp[1-*]_max_hyst 325 Temperature hysteresis value for max limit. 326 Unit: millidegree Celsius 327 Must be reported as an absolute temperature, NOT a delta 328 from the max value. 329 RW 330 331 temp[1-*]_min_hyst 332 Temperature hysteresis value for min limit. 333 Unit: millidegree Celsius 334 Must be reported as an absolute temperature, NOT a delta 335 from the min value. 336 RW 337 338 temp[1-*]_input Temperature input value. 339 Unit: millidegree Celsius 340 RO 341 342 temp[1-*]_crit Temperature critical max value, typically greater than 343 corresponding temp_max values. 344 Unit: millidegree Celsius 345 RW 346 347 temp[1-*]_crit_hyst 348 Temperature hysteresis value for critical limit. 349 Unit: millidegree Celsius 350 Must be reported as an absolute temperature, NOT a delta 351 from the critical value. 352 RW 353 354 temp[1-*]_emergency 355 Temperature emergency max value, for chips supporting more than 356 two upper temperature limits. Must be equal or greater than 357 corresponding temp_crit values. 358 Unit: millidegree Celsius 359 RW 360 361 temp[1-*]_emergency_hyst 362 Temperature hysteresis value for emergency limit. 363 Unit: millidegree Celsius 364 Must be reported as an absolute temperature, NOT a delta 365 from the emergency value. 366 RW 367 368 temp[1-*]_lcrit Temperature critical min value, typically lower than 369 corresponding temp_min values. 370 Unit: millidegree Celsius 371 RW 372 373 temp[1-*]_lcrit_hyst 374 Temperature hysteresis value for critical min limit. 375 Unit: millidegree Celsius 376 Must be reported as an absolute temperature, NOT a delta 377 from the critical min value. 378 RW 379 380 temp[1-*]_offset 381 Temperature offset which is added to the temperature reading 382 by the chip. 383 Unit: millidegree Celsius 384 Read/Write value. 385 386 temp[1-*]_label Suggested temperature channel label. 387 Text string 388 Should only be created if the driver has hints about what 389 this temperature channel is being used for, and user-space 390 doesn't. In all other cases, the label is provided by 391 user-space. 392 RO 393 394 temp[1-*]_lowest 395 Historical minimum temperature 396 Unit: millidegree Celsius 397 RO 398 399 temp[1-*]_highest 400 Historical maximum temperature 401 Unit: millidegree Celsius 402 RO 403 404 temp[1-*]_reset_history 405 Reset temp_lowest and temp_highest 406 WO 407 408 temp_reset_history 409 Reset temp_lowest and temp_highest for all sensors 410 WO 411 412 Some chips measure temperature using external thermistors and an ADC, and 413 report the temperature measurement as a voltage. Converting this voltage 414 back to a temperature (or the other way around for limits) requires 415 mathematical functions not available in the kernel, so the conversion 416 must occur in user space. For these chips, all temp* files described 417 above should contain values expressed in millivolt instead of millidegree 418 Celsius. In other words, such temperature channels are handled as voltage 419 channels by the driver. 420 421 Also see the Alarms section for status flags associated with temperatures. 422 423 424 ************ 425 * Currents * 426 ************ 427 428 curr[1-*]_max Current max value 429 Unit: milliampere 430 RW 431 432 curr[1-*]_min Current min value. 433 Unit: milliampere 434 RW 435 436 curr[1-*]_lcrit Current critical low value 437 Unit: milliampere 438 RW 439 440 curr[1-*]_crit Current critical high value. 441 Unit: milliampere 442 RW 443 444 curr[1-*]_input Current input value 445 Unit: milliampere 446 RO 447 448 curr[1-*]_average 449 Average current use 450 Unit: milliampere 451 RO 452 453 curr[1-*]_lowest 454 Historical minimum current 455 Unit: milliampere 456 RO 457 458 curr[1-*]_highest 459 Historical maximum current 460 Unit: milliampere 461 RO 462 463 curr[1-*]_reset_history 464 Reset currX_lowest and currX_highest 465 WO 466 467 curr_reset_history 468 Reset currX_lowest and currX_highest for all sensors 469 WO 470 471 Also see the Alarms section for status flags associated with currents. 472 473 ********* 474 * Power * 475 ********* 476 477 power[1-*]_average Average power use 478 Unit: microWatt 479 RO 480 481 power[1-*]_average_interval Power use averaging interval. A poll 482 notification is sent to this file if the 483 hardware changes the averaging interval. 484 Unit: milliseconds 485 RW 486 487 power[1-*]_average_interval_max Maximum power use averaging interval 488 Unit: milliseconds 489 RO 490 491 power[1-*]_average_interval_min Minimum power use averaging interval 492 Unit: milliseconds 493 RO 494 495 power[1-*]_average_highest Historical average maximum power use 496 Unit: microWatt 497 RO 498 499 power[1-*]_average_lowest Historical average minimum power use 500 Unit: microWatt 501 RO 502 503 power[1-*]_average_max A poll notification is sent to 504 power[1-*]_average when power use 505 rises above this value. 506 Unit: microWatt 507 RW 508 509 power[1-*]_average_min A poll notification is sent to 510 power[1-*]_average when power use 511 sinks below this value. 512 Unit: microWatt 513 RW 514 515 power[1-*]_input Instantaneous power use 516 Unit: microWatt 517 RO 518 519 power[1-*]_input_highest Historical maximum power use 520 Unit: microWatt 521 RO 522 523 power[1-*]_input_lowest Historical minimum power use 524 Unit: microWatt 525 RO 526 527 power[1-*]_reset_history Reset input_highest, input_lowest, 528 average_highest and average_lowest. 529 WO 530 531 power[1-*]_accuracy Accuracy of the power meter. 532 Unit: Percent 533 RO 534 535 power[1-*]_cap If power use rises above this limit, the 536 system should take action to reduce power use. 537 A poll notification is sent to this file if the 538 cap is changed by the hardware. The *_cap 539 files only appear if the cap is known to be 540 enforced by hardware. 541 Unit: microWatt 542 RW 543 544 power[1-*]_cap_hyst Margin of hysteresis built around capping and 545 notification. 546 Unit: microWatt 547 RW 548 549 power[1-*]_cap_max Maximum cap that can be set. 550 Unit: microWatt 551 RO 552 553 power[1-*]_cap_min Minimum cap that can be set. 554 Unit: microWatt 555 RO 556 557 power[1-*]_max Maximum power. 558 Unit: microWatt 559 RW 560 561 power[1-*]_crit Critical maximum power. 562 If power rises to or above this limit, the 563 system is expected take drastic action to reduce 564 power consumption, such as a system shutdown or 565 a forced powerdown of some devices. 566 Unit: microWatt 567 RW 568 569 Also see the Alarms section for status flags associated with power readings. 570 571 ********** 572 * Energy * 573 ********** 574 575 energy[1-*]_input Cumulative energy use 576 Unit: microJoule 577 RO 578 579 580 ************ 581 * Humidity * 582 ************ 583 584 humidity[1-*]_input Humidity 585 Unit: milli-percent (per cent mille, pcm) 586 RO 587 588 589 ********** 590 * Alarms * 591 ********** 592 593 Each channel or limit may have an associated alarm file, containing a 594 boolean value. 1 means than an alarm condition exists, 0 means no alarm. 595 596 Usually a given chip will either use channel-related alarms, or 597 limit-related alarms, not both. The driver should just reflect the hardware 598 implementation. 599 600 in[0-*]_alarm 601 curr[1-*]_alarm 602 power[1-*]_alarm 603 fan[1-*]_alarm 604 temp[1-*]_alarm 605 Channel alarm 606 0: no alarm 607 1: alarm 608 RO 609 610 OR 611 612 in[0-*]_min_alarm 613 in[0-*]_max_alarm 614 in[0-*]_lcrit_alarm 615 in[0-*]_crit_alarm 616 curr[1-*]_min_alarm 617 curr[1-*]_max_alarm 618 curr[1-*]_lcrit_alarm 619 curr[1-*]_crit_alarm 620 power[1-*]_cap_alarm 621 power[1-*]_max_alarm 622 power[1-*]_crit_alarm 623 fan[1-*]_min_alarm 624 fan[1-*]_max_alarm 625 temp[1-*]_min_alarm 626 temp[1-*]_max_alarm 627 temp[1-*]_lcrit_alarm 628 temp[1-*]_crit_alarm 629 temp[1-*]_emergency_alarm 630 Limit alarm 631 0: no alarm 632 1: alarm 633 RO 634 635 Each input channel may have an associated fault file. This can be used 636 to notify open diodes, unconnected fans etc. where the hardware 637 supports it. When this boolean has value 1, the measurement for that 638 channel should not be trusted. 639 640 fan[1-*]_fault 641 temp[1-*]_fault 642 Input fault condition 643 0: no fault occurred 644 1: fault condition 645 RO 646 647 Some chips also offer the possibility to get beeped when an alarm occurs: 648 649 beep_enable Master beep enable 650 0: no beeps 651 1: beeps 652 RW 653 654 in[0-*]_beep 655 curr[1-*]_beep 656 fan[1-*]_beep 657 temp[1-*]_beep 658 Channel beep 659 0: disable 660 1: enable 661 RW 662 663 In theory, a chip could provide per-limit beep masking, but no such chip 664 was seen so far. 665 666 Old drivers provided a different, non-standard interface to alarms and 667 beeps. These interface files are deprecated, but will be kept around 668 for compatibility reasons: 669 670 alarms Alarm bitmask. 671 RO 672 Integer representation of one to four bytes. 673 A '1' bit means an alarm. 674 Chips should be programmed for 'comparator' mode so that 675 the alarm will 'come back' after you read the register 676 if it is still valid. 677 Generally a direct representation of a chip's internal 678 alarm registers; there is no standard for the position 679 of individual bits. For this reason, the use of this 680 interface file for new drivers is discouraged. Use 681 individual *_alarm and *_fault files instead. 682 Bits are defined in kernel/include/sensors.h. 683 684 beep_mask Bitmask for beep. 685 Same format as 'alarms' with the same bit locations, 686 use discouraged for the same reason. Use individual 687 *_beep files instead. 688 RW 689 690 691 *********************** 692 * Intrusion detection * 693 *********************** 694 695 intrusion[0-*]_alarm 696 Chassis intrusion detection 697 0: OK 698 1: intrusion detected 699 RW 700 Contrary to regular alarm flags which clear themselves 701 automatically when read, this one sticks until cleared by 702 the user. This is done by writing 0 to the file. Writing 703 other values is unsupported. 704 705 intrusion[0-*]_beep 706 Chassis intrusion beep 707 0: disable 708 1: enable 709 RW 710 711 712 sysfs attribute writes interpretation 713 ------------------------------------- 714 715 hwmon sysfs attributes always contain numbers, so the first thing to do is to 716 convert the input to a number, there are 2 ways todo this depending whether 717 the number can be negative or not: 718 unsigned long u = simple_strtoul(buf, NULL, 10); 719 long s = simple_strtol(buf, NULL, 10); 720 721 With buf being the buffer with the user input being passed by the kernel. 722 Notice that we do not use the second argument of strto[u]l, and thus cannot 723 tell when 0 is returned, if this was really 0 or is caused by invalid input. 724 This is done deliberately as checking this everywhere would add a lot of 725 code to the kernel. 726 727 Notice that it is important to always store the converted value in an 728 unsigned long or long, so that no wrap around can happen before any further 729 checking. 730 731 After the input string is converted to an (unsigned) long, the value should be 732 checked if its acceptable. Be careful with further conversions on the value 733 before checking it for validity, as these conversions could still cause a wrap 734 around before the check. For example do not multiply the result, and only 735 add/subtract if it has been divided before the add/subtract. 736 737 What to do if a value is found to be invalid, depends on the type of the 738 sysfs attribute that is being set. If it is a continuous setting like a 739 tempX_max or inX_max attribute, then the value should be clamped to its 740 limits using clamp_val(value, min_limit, max_limit). If it is not continuous 741 like for example a tempX_type, then when an invalid value is written, 742 -EINVAL should be returned. 743 744 Example1, temp1_max, register is a signed 8 bit value (-128 - 127 degrees): 745 746 long v = simple_strtol(buf, NULL, 10) / 1000; 747 v = clamp_val(v, -128, 127); 748 /* write v to register */ 749 750 Example2, fan divider setting, valid values 2, 4 and 8: 751 752 unsigned long v = simple_strtoul(buf, NULL, 10); 753 754 switch (v) { 755 case 2: v = 1; break; 756 case 4: v = 2; break; 757 case 8: v = 3; break; 758 default: 759 return -EINVAL; 760 } 761 /* write v to register */