Question

Is there a way to know the return code or process ID of the process which gets executed when the privileged helper tool is installed as a launchdaemon and launched via SMJobSubmit().

I have an application which to execute some tasks in privileged manner uses the SMJobSubmit API as mentioned here.

Now in order to know whether the tasks succeeded or not, I will have to do one of the following.

1. The best option is to get the return code of the executable that ran.
2. Another option would be if I could create a pipe between my application and the launchd.
3. If the above two are not possible, I will have to resort to some hack like writing a file in /tmp location and reading it from my app.

I guess SMJobSubmit internally submits the executable with a launchdaemon dictionary to the launchd which is then responsible for its execution. So is there a way I could query launchd to find out the return code for the executable run with the label “mylabel”.

Answer 1

There is no way to do this directly.

SMJobSubmit is a simple wrapper around a complicated task. It also returns synchronously despite launching a task asynchronously. So, while it can give you an error if it fails to submit the job, if it successfully submits a job that fails to run, there is no way to find that out.

So, you will have to explicitly write some code to communicate from your helper to your app, to report that it’s up and running.

If you’ve already built some communication mechanism (signals, files, Unix or TCP sockets, JSON-RPC over HTTP, whatever), just use that.

If you’re designing something from scratch, XPC may be the best answer. You can’t use XPC to launch your helper (since it’s privileged), but you can manually create a connection by registering a Mach service and calling xpc_connection_create_mach_service.