Where to start with a launchd daemon?

I'm finding it difficult to navigate the macOS documentation.

Yeah, I sympathise; documentation for this part of the system is not as well maintained as it should be. Where you have problems I recommend that you file bugs against the docs; that’ll help DevPubs understand where the rough edges are.

Having said that, a lot of this stuff is covered, at least at the reference level, in the system man pages; I’ll provide some links below but, if you have Xcode installed, you can access man pages from Terminal via the traditional UNIX

man

This sounds exactly what I need to know as I'd like my service started on demand and it currently listens on a socket for clients.

Right. In general macOS daemons should strive to launch on demand. If the only thing your daemon does is respond to network requests, having launchd open a listening socket and launch your daemon when folks connect to that socket is the right approach.

However when I take a look at that sample it first calls kqueue() which I cannot find any documentation for on the developer docs search page.

This is covered by the

kqueue

Note that kqueues are just a mechanism to integrate various event sources into an event loop. Most folks on Darwin platforms use:

• NSRunLoop, if they’re already using high-level frameworks

• dispatch event sources (see here), if they want to avoid the high-level frameworks for some reason

SampleD hasn’t been updated in a while, which is why it still uses kqueues.

Then the sample calls a bunch of XPC calls (like

launch_data_dict_lookup

) that are all marked deprecated.

Yeah, that could be clearer. In

<launch.h>

launch_activate_socket

Please do file a bug against SampleD requesting it be updated to use the new stuff.

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Apple Developer Relations, Developer Technical Support, Core OS/Hardware

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Thanks for your reply, Filed bug 27357721

- James

So it's been almost three years since this question was asked, and I see that SampleD.c has not been updated to use the launch_activate_socket function instead of the deprecated launch_data_* functions. Is there a quick summary of how to use the launch_activate_socket function to perform the checkin with launchd when your Launch Daemon starts up?