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A clean and documented OOP wrapper around the AppleSMC IOService on Mac OS X.
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SMCWrapper See 1b94d75 Dec 11, 2014
examples Add example Xcode Project Oct 3, 2014
LICENSE Base Commit Sep 30, 2014 Update Apr 25, 2018

This repository is ARCHIVED and UNMAINTAINED. I no longer have any systems running Mac OS X either, so continued development will not happen.


A little OOP colour around a grey API.

What is SMCWrapper?

If you've ever looked under the hood at a Mac OS X application for controlling fans or reading sensor data, then you will undoubtedly have seen two files - smc.c and smc.h. Used in just about every project that relies upon reading SMC values.

The problem is, these files have become something of a dark magic - with no real comments or explanations anywhere, no bindings for NS* classes and a lack of any OOP implementation.

To combat that I've done the following;

  • Wrapped the functionality up in to a convenient class
  • Wrote some fairly extensive comments
  • Included the ability to read values in to NSNumber and NSString objects.
No Writing to SMC Keys

If people do want this then I will add it in, at some point. Alternatively, fork this and give me a pull request!

Limited support for dataTypes

Well, this is actually a lie - as this supports more data types than some of the older copies of smc.c that are still dotted around the internet. However, don't go expecting every possible SMC key to return a valid value. If you find a key that doesn't, please fill in an "Issue" here on Github and I'll have a look at it. (Or, once again, fork it!)

Written by someone with a poor grasp of Objective-C

I haven't used Objective C since the days of the iPhone SDK (that's before the iPad came along and it was renamed the iOS SDK for you newcomers! ;)) - so I'm very much rusty!

Staggeringly Simple

Retrieve an instance of SMCWrapper
SMCWrapper *smc = [SMCWrapper sharedWrapper];
Read a key in to an NSNumber
NSNumber *CPUTemp;
[smc readKey:"TC0P" intoNumber:&CPUTemp];
Read a key in to an NSString
NSString *fanRPM;
[smc readKey:"F0Ac" asString:&fanRPM]; 

An example

int main(int argc, const char * argv[])
    SMCWrapper *smc = [SMCWrapper sharedWrapper];

    // TC0P => CPU Temperature
    NSNumber *temp;
    if ( [smc readKey:"TC0P" intoNumber:&temp] ){
        NSLog(@"CPU Temperature:\t %@C", [temp stringValue]);
    // F0Ac => Fan0 Actual RPM
    NSNumber *fanRPM;
    if ( [smc readKey:"F0Ac" intoNumber:&fanRPM] ){
        NSLog(@"Fan #0 RPM:\t %@", [fanRPM stringValue]);

    // F0Mn => Min RPM
    NSString *minRPM;
    if ( [smc readKey:"F0Mn" asString:&minRPM] ){
        NSLog(@"Fan #0 Min RPM:\t %@", minRPM);

    // F0Mx => Max RPM
    NSString *maxRPM;
    if ( [smc readKey:"F0Mx" asString:&maxRPM] ){
        NSLog(@"Fan #0 Max RPM:\t %@", maxRPM);
    return 0;

On my 13" Early 2004 MacBook Air, this currently produces..

2014-09-30 02:48:22.485 SMCInfo[56428:386055] CPU Temperature: 42.75C
2014-09-30 02:48:22.487 SMCInfo[56428:386055] Fan #0 RPM: 1203
2014-09-30 02:48:22.487 SMCInfo[56428:386055] Fan #0 Min RPM: 1200.00
2014-09-30 02:48:22.488 SMCInfo[56428:386055] Fan #0 Max RPM: 6500.00


I'm fairly certain that the original files were wrote by a guy named devnull, but released under the GNU General Public License all the same. As such, this class itself is also released under the GNU General Public License.

Special mentions are deserved for @HHoltmann - Hendrik Holtmann, for his smcFanControl repository which provided some good reading, @stny - Naoya SATO for his Thermo repository - which included an smc.c version which supported a good number of data types.