Receiving power notifications (especially shutdown) on Mac OSX


Question or issue on macOS:

I’m writing an application in C for the Mac (Leopard) that needs to do some work on receipt of power notifications, e.g. sleep, wake-up, shutdown, restart. It runs via launchd as a launchagent on login then begins monitoring for notifications. The code I’m using to do this is as follows:

/* ask for power notifications */
static void StartPowerNotification(void)
    static io_connect_t rootPort;   
    IONotificationPortRef notificationPort;
    io_object_t notifier;

    rootPort = IORegisterForSystemPower(&rootPort, ¬ificationPort, 
                                        PowerCallback, ¬ifier);
    if (!rootPort) 
        exit (1);

    CFRunLoopAddSource (CFRunLoopGetCurrent(),  

/* perform actions on receipt of power notifications */
void PowerCallback (void *rootPort, io_service_t y, 
                    natural_t msgType, void *msgArgument)
    switch (msgType) 
        case kIOMessageSystemWillSleep:
            /* perform sleep actions */

        case kIOMessageSystemHasPoweredOn:
            /* perform wakeup actions */

        case kIOMessageSystemWillRestart:
            /* perform restart actions */

        case kIOMessageSystemWillPowerOff:
            /* perform shutdown actions */

However, only the top two for sleep and wake (kIOMessageSystemWillSleep and kIOMessageSystemHasPoweredOn) ever get called. I never get any notifcations for restart or shutdown (kIOMessageSystemWillRestart and kIOMessageSystemWillPowerOff).

Am I doing something wrong? Or is there another API that would give me the restart and shutdown notifications? I’d prefer to keep it as a C program (as thats what I’m familiar with) but am open to any sensible suggestions of alternatives (I’ve had a look at login/logout hooks but these seem to be deprecated in favour of launchd).

Thanks in advance for any help/tips!

How to solve this problem?

Solution no. 1:

I know you can register for the NSWorkspaceWillPowerOffNotification notification from NSWorkspace, which is not a C function but does work.

#import "WorkspaceResponder.h"

int main (int argc, const char * argv[]) {
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
    NSNotificationCenter *nc = [[NSWorkspace sharedWorkspace] notificationCenter];
    WorkspaceResponder *mainController = [[WorkspaceResponder alloc] init];

    //register for shutdown notications
    [nc addObserver:mainController
          name:NSWorkspaceWillPowerOffNotification object:nil];
    [[NSRunLoop currentRunLoop] run];
    [pool release];
    return 0;

Then in WorkspaceResponder.m:

- (void) computerWillShutDownNotification:(NSNotification *)notification {
    NSLog(@"Received Shutdown Notification");

Solution no. 2:

Using IORegisterForSystemPower doesn’t provide the events you seek. Quoting from function documentation :

/*! @function IORegisterForSystemPower
@abstract Connects the caller to the Root Power Domain IOService
for the purpose of receiving sleep & wake notifications for the system.
Does not provide system shutdown and restart notifications.

Hope this helps!