[launchd-dev] Cause of "Service cannot load in requested session"?

[James Bucanek]

Greetings,

I finally had a chance to run this to ground. Here's what I discovered:

Basically, LimitLoadToSessionType=Background is broken. (bug report 
#23536982)

I was able to narrow down the problem to this simple example. First, 
write the following plist file to 
~/Library/LaunchAgents/info.test.agent.plist (edit the path, if you want 
to play along at home):

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" 
"http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>Label</key>
<string>info.test.agent</string>
<key>LimitLoadToSessionType</key>
<string>Background</string>
<key>ProgramArguments</key>
<array>
<string>/usr/bin/touch</string>
<string>/Users/james/Desktop/TestAgentDidRun.txt</string>
</array>
<key>RunAtLoad</key>
<true/>
</dict>
</plist>

Now, restart the computer. What *should* happen is /usr/bin/touch should 
execute when the background session for the user is created, creating 
the /Users/james/Desktop/TestAgentDidRun.txt file.

What actually happens is nothing. The agent is never started and the 
file is never created. The behavior is the same in 10.10 and 10.11.

When the Aqua session is finally created, you still get this message in 
the console:

Nov 12 22:14:41 Jamess-Mac-Pro otherbsd[261]: Failed to bootstrap agent: 
path = /Users/james/Library/LaunchAgents/info.test.agent.plist, error = 
134: Service cannot load in requested session

But, as previously discussed, this just the agent getting loaded into 
the Aqua session, and failing because it can't.

I was also able to confirm Damien's workaround of manually reloading the 
service once the Aqua session is created. I have another Aqua-only GUI 
agent. I've modified it so that it looks to see if my (Background) 
scheduler process is running. If it isn't running, but is installed, it 
reloads it by executing the following command:

     launchctl bootstrap user/<uid> 
~/Library/LaunchAgents/com.qrecall.scheduler.plist

That starts the scheduler process in the background session.

This doesn't completely solve my problem, because what I *really* want 
is for the Background agent to start before the user logs in. But at 
least it will now start when the user does log in, and it continues to 
run after they log out.

James