[launchd-dev] launch_msg(): Socket is not connected

[Quinn]

At 18:44 +0530 8/6/09, Arjun SM wrote:
>I am getting this message when i am trying to launch my application 
>which is a LaunchAgent. This message comes only when multiple Users 
>are logged in.

Yeah, your script, as its written, is never going to work.  The 
problem is that, except when run as root, launchctl finds the right 
launchd to talk to by looking it up in the Mach bootstrap namespace. 
Your script is always running in one user's namespace, so will always 
end up talk to that user's launchd (which ends badly because of 
permissions).

The launchd story is a quite weak when it comes to installing and 
upgrading agents where there are users logged in.  This is a well 
known problem <rdar://problem/5476420> but, alas, I don't have any 
good news to share with you on this front.

This problem breaks down as follows:

o upgrade -- There /is/ a reasonable way to handle the upgrade 
scenario.  Most agents are running on behalf of a daemon.  In that 
case you can overwrite the agent on disk and then tell the daemon to 
signal all of the agents to quit.  They will be relaunched by their 
respective launchd's, this time running the new code.  You have to be 
a little careful, but this approach works reasonably well.

o first install -- There isn't a good way to handle the first install 
case.  You can start the agent in the GUI context that you're running 
in, but starting agents in other existing GUI contexts is tricky.  In 
general I'd recommend you /not/ try to solve this.  Non-foreground 
GUI users will have to log out and log back in to pick up your agent. 
If that's a problem (for example, you're installing security 
software), force a restart in that case.

Keep in mind that the multiple GUI logins via fast user switching is 
an edge case that 90% of your users will never encounter.

S+E
-- 
Quinn "The Eskimo!"                    <http://www.apple.com/developer/>
Apple Developer Relations, Developer Technical Support, Core OS/Hardware