Lock screen by API in macOS

Question

Is there an API, that can lock the screen as the menu bar entry you can add from Keychain preferences?

This Keychain function is (was) lock

Answer 1

It's not officially documented and uses private API, but the following works on MacOS 10.10 (and maybe also on earlier systems):

// lockscreen.c
extern int SACLockScreenImmediate ( void );

int main ( ) {
    return SACLockScreenImmediate();
}

Build with:

clang -F /System/Library/PrivateFrameworks -framework login -o lockscreen lockscreen.c 

Now calling ./lockscreen will lock the screen immediately, regardless what the user has configured in their security preferences (whether to lock on screensaver/system sleep) and without logging the user out. This is the function the system uses internally for locking the screen.

I strongly discourage using it, it may break your app and I'm not even sure I am calling it correctly (maybe it needs arguments, maybe it has a return value), so it may even break your whole system (temporarily - reboot will fix everything), who knows. I just wanted to post that somewhere for documentation.

If someone with better hacker skills than me can analyze this call some more, this would be nice and useful.