Issues with LaunchAgent and LaunchDaemon

Question

gamakaze OP

Created 4d

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Boosts 0

Participants 2

I have this application that is divided in 3 parts.

A server that handles all the networking code
A agent that handles all System related code
A manager (NSApplication) to interact with the other two processes.

Goals

All three process should be kept alive if they crash
All three processes must not restart if the user quits them though the NSApplication
They need to run during the login window.

My current set up using LaunchD is as follows.

My Server process plist (relevant part) saved in System/LaunchDaemons

key>MachServices</key>
<dict>
	<key>com.myCompany.Agent.xpc</key>
	<true/>
	<key>com.myCompany.Manager.xpc</key>
	<true/>
</dict>
<key>ProgramArguments</key>
<array>
	<string>PathToExecutable</string>
	<string>-service</string>
</array>
<key>RunAtLoad</key>
<false/>

My agent plist (saved in System/LaunchAgent)

<key>QueueDirectories</key>
<array>
	<string>PathToDirectory</string>
</array>
<key>RunAtLoad</key>
<false/>
<key>ProgramArguments</key>
<array>
	<string>PathToExecutable</string>
	<string>service</string>
</array>

my Manager app plist (saved in System/LaunchAgent)

<key>LimitLoadToSessionType</key>
        <string>Aqua</string>
    <key>RunAtLoad</key>
        <false/>
    <key>ProgramArguments</key>
        <array>
            <string>PathToExecutable</string>
        </array>
    <key>MachServices</key>
        <dict>
	        <key>com.myCompany.Agent.manager.xpc</key>
	        <true/>
        </dict>

Currently I have another app that saves a file to the path of the QueueDirectories which triggers the launch of my Agent which then triggers the Server and Manager by starting a XPC Connection. QueueDirectories keeps the Agent alive (and hence all other processes) til file is removed and processes are quited through the manager.

XPC Connections

Server listens for a connection from agent and manager
Manager listens for a connection from agent and starts a connection with server
Agent starts a connection with Manager and Server

Agent and Manager are owned by the user and server by root

The problems

When I start Agent by saving a file in the QueueDirectories path and connect to the Server over xpc I end up with two Agents, one owned by the user (the one I expect) and one owned by root.

But if I manually start the Agent I do not have that problem.

As I mentioned before, the server listens for a connection from the Agent.

How do I stop getting two instances? or what is a better way to approach this?

Boost

Answer 1

DTS Engineer OP

Apple

3d

All three processes must not restart if the user quits them

It’s impossible to achieve this goal for a launchd agent. That’s because:

A launchd agent must necessarily be running on the user associated with its session, otherwise it won’t be able to do agent-y things.
If it is, the user can kill it.

The only solution here is to structure your product so that:

The core functionality lives in the daemon, which the user can’t kill [1].
The user doesn’t gain anything by killing your agent.

I end up with two Agents, one owned by the user (the one I expect) and one owned by root.

It’s not clear how that comes about. One obvious way this can happen is if your agent loads into the pre-login session. However, you haven’t listed LoginWindow in your LimitLoadToSessionType. However^2, you earlier said that “They need to run during the login window”, which suggests that you should be listing it there. So I’m a bit confused.

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

[1] Unless they’re as an admin user, and you can’t protect yourself from admin users.

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