999Running Repetitive Jobs on OSX

Traditionally Unix systems use crontab to schedule and run repetitive jobs, OSX uses launchd, an init and operating system service management daemon.

Here is a script that call my index.php every 120 seconds. (I am download snow webcams in the index.php.)

<?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>org.trembl.snow</string>
  <key>ServiceDescription</key>
  <string>Getting Snow Pictures</string>
  <key>ProgramArguments</key>
  <array>
    <string>/Applications/XAMPP/bin/php</string>
    <string>/Applications/XAMPP/xamppfiles/htdocs/snow/index.php</string>
  </array>
  <key>RunAtLoad</key>
  <true/>
  <key>StartInterval</key>
  <integer>120</integer>
</dict>
</plist>

In Xcode, the same script looks like this:

Troubleshooting

I made a couple of errors, trying to get the script to run.

  1. Permissions sudo chown <user>:staff org.trembl.snow.plist
    Incorrect permissions also cause the Load failed: 122: Path had bad ownership/permissions

  2. The name of the file and the Label need to match. org.trembl.snow and org.trembl.snow.plist

  3. The plist need to be placed into ~/Library/LaunchAgents.

  4. If your Program has arguments, they need to be specified in an array:

    <key>ProgramArguments</key>
    <array>
    <string>/Applications/XAMPP/bin/php</string>
    <string>/Applications/XAMPP/xamppfiles/htdocs/snow/index.php</string>
    </array>
  5. Both strings need to be absolute. I got this error: Load failed: 122: Path had bad ownership/permissions, which was caused by only saying index.php instead of the whole absolute path.

  6. Use launchctl bootstrap and not the obsolete launchctl load.

  7. Launch with sudo launchctl bootstrap gui/`id -u` ~/Library/LaunchAgents/org.trembl.snow.plist

  8. Stop: sudo launchctl bootoutp gui/`id -u` ~/Library/LaunchAgents/org.trembl.snow.plist

327Launchd – Reacting to System Events

launchd can be used to montor files and folder and execute certain actions when these files or folders change. Especially useful when an App crashes and writes a log to the CrashReporter. Tutorial, Lingon Helper App