README
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go-smc
Golang library to read temperatures and fan speeds from the macOS System Management Controller (SMC). Works on both Intel and Apple Silicon Macs.
go get github.com/caseymrm/go-smc
smc.OpenSMC()
defer smc.CloseSMC()
fmt.Println("CPU temperature:", smc.ReadTemperature(), "°C")
fmt.Println("Fan speeds:", smc.ReadFanSpeeds(), "RPM")
for key, tempC := range smc.ReadTemperatures() {
fmt.Printf(" %s = %.2f °C\n", key, tempC)
}
Apple Silicon
Both fan and temperature reads go through AppleSMC on all architectures — only the keys and data type differ:
| Reading | Intel | Apple Silicon |
|---|---|---|
| CPU temperature | TC0P (sp78) |
Tp01…Tp16 (flt) |
| Fan speed | F0Ac…F17Ac (fpe2) |
F0Ac…F17Ac (flt) |
ReadTemperature() returns the hottest sensor across whatever keys the SoC populates (M1 reports fewer than M2/M3/M4). ReadTemperatures() returns the full map of populated sensors if you need per-cluster detail.
Fanless Macs (M1/M2 MacBook Air, Mac mini, etc.) have no F*Ac keys at all; ReadFanSpeeds() returns an empty slice there.
License
MIT — see LICENSE.
The C in smc.c / smc.h is an independent reimplementation written against two references, both cited in the file headers:
- Apple's APSL-licensed PowerManagement source, for the AppleSMC IOKit ABI (struct layout, ioctl indices).
- beltex/SMCKit (MIT, Swift), for the shape of a clean reader.
It is not derived from the GPL "Apple SMC Tool" by devnull (2006) that's copied across many SMC projects. Earlier versions of this repo bundled that GPL file under an MIT LICENSE, which was an error; #1 tracked and resolved that conflict.
Documentation
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Overview ¶
Package smc reads sensor values (temperatures, fan speeds) from the macOS AppleSMC kernel extension. It works on both Intel and Apple Silicon Macs; the difference is the set of keys and their data type:
- Intel: temperatures live under TC0P / TC0E / TC0F (sp78), fans under F0Ac…F17Ac (fpe2).
- Apple Silicon: temperatures live under Tp01…Tp16 (flt — IEEE 754 single precision), fans under F0Ac…F17Ac (also flt).
AppleSMC fan keys do not exist at all on fanless Macs (e.g. M1/M2 MacBook Air); ReadFanSpeeds returns an empty slice on those.
Index ¶
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
func OpenSMC ¶
func OpenSMC()
OpenSMC keeps the SMC connection open for the lifetime of the process. Otherwise each Read* call opens and closes it.
func ReadFanSpeeds ¶
func ReadFanSpeeds() []int
ReadFanSpeeds returns the current speed of each active fan in RPM, in fan-index order. Returns an empty slice on fanless Macs (M1/M2 MacBook Air, etc.) where the SMC has no F*Ac keys.
Reads keys F0Ac through F17Ac and stops at the first one that does not respond. AppleSMC reports these as sp78/fpe2 on Intel and as IEEE-754 float on Apple Silicon; both formats are handled.
func ReadTemperature ¶
func ReadTemperature() float64
ReadTemperature returns a representative CPU temperature in degrees Celsius, or 0.0 if no temperature sensor could be read.
- On Intel, this is the TC0P (CPU proximity) sensor.
- On Apple Silicon, this is the maximum across all populated per-cluster CPU sensors (Tp01…Tp16) — i.e. the hottest core cluster, which is generally the most useful single value for thermal monitoring.
func ReadTemperatures ¶
ReadTemperatures returns every CPU-cluster temperature sensor the kernel acknowledges, keyed by SMC key (e.g. "Tp01"). On Intel this will typically be a single entry under "TC0P"; on Apple Silicon it will be several Tp* entries. Empty if no sensors respond.
Types ¶
This section is empty.
Source Files