Why Does My Launchd Job Suddenly Stop

Question

OSX 10.9.5MacBook Air 11 Inch Late 2010I have a launchd job running on this MacBook. The job runs a shell script every four minutes. That shell script captures a webcam image and uploads it to my website.Most of the time this works just fine. But, every once in a while the launchd job simply stops. if I unload and reload the plist file, the job starts running again. Other jobs continue to run without problems.What can stop a job from running?The job was created with Lingon X.&lt;?xml version&#x3D;"1.0" encoding&#x3D;"UTF-8"?&gt;&lt;!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"&gt;&lt;plist version&#x3D;"1.0"&gt;&lt;dict&gt;  &lt;key&gt;Disabled&lt;/key&gt;  &lt;false/&gt;  &lt;key&gt;EnvironmentVariables&lt;/key&gt;  &lt;dict&gt;  &lt;key&gt;PATH&lt;/key&gt;  &lt;string&gt;/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/opt/X11/bin:/usr/local/sb in&lt;/string&gt;  &lt;/dict&gt;  &lt;key&gt;Label&lt;/key&gt;  &lt;string&gt;com.mgnewman.webcam&lt;/string&gt;  &lt;key&gt;ProgramArguments&lt;/key&gt;  &lt;array&gt;  &lt;string&gt;/Users/mnewman/bin/chaamcam.sh&lt;/string&gt;  &lt;/array&gt;  &lt;key&gt;QueueDirectories&lt;/key&gt;  &lt;array/&gt;  &lt;key&gt;RunAtLoad&lt;/key&gt;  &lt;true/&gt;  &lt;key&gt;StartInterval&lt;/key&gt;  &lt;integer&gt;240&lt;/integer&gt;  &lt;key&gt;WatchPaths&lt;/key&gt;  &lt;array/&gt;&lt;/dict&gt;&lt;/plist&gt;

Camelot · Accepted Answer

The first question I have is what do the logs have to say about it?Any error condition should be logged in /var/log/system.log so that&#x27;s the place to start.Beyond that, processes may get throttled if they spawn too frequently, and a job may not be kicked off if its previous incarnation is still running - is it possible that it&#x27;s taking more than 4 minutes for the script to run, and that&#x27;s blocking the next invocation?In either case, you should remove the RunAtLoad key from your .plist, since it doesn&#x27;t apply here (man launchd.plist has more detail on this key).

Buadhai · Answer

Thank you.I don&#x27;t see anything in the system.log that tells me what&#x27;s going on. The shell script that I run keeps a log, so I can see the exact time that it happened because log entries stop. (And, since the script captures and time stamps a photo, I can also see when the last photo was processed.")Your hint that the script might be taking more than four minutes to run helped a lot. Looking at the log that the script keeps, I can see that during the last successful run, the script seems to have started, but never finished. I think I know what caused this and have removed the offending lines.I have also removed the RunAtLoad key from the plist.So far, so good.Thanks for your help. I learned something. Well, more than one thing.