OSX launchd and inetd services

Apple has an epic writeup of how daemons should be written for OS X, Mach execution contexts, IPC and more in TN2083. This post is just some quick summary notes.

launchd is roughly equivalent to cron, init.d, and xinetd all rolled into one. Use it by dropping a plist into one of these directories:

• /Library/LaunchDaemons runs as root on system startup
• /Library/LaunchAgents runs as the user on login
• ~/Library/LaunchAgents runs as the user for the specific user login

There is also /System/Library/Launch{Agents,Daemons} which is for the jobs installed by the OS. Use the directories above for any custom jobs.

List launchd jobs with

launchctl list

Start:

sudo launchctl load /Library/LaunchDaemons/com.myorg.somejob.plist

Stop:

sudo launchctl unload /Library/LaunchDaemons/com.myorg.somejob.plist

There are many different options for jobs, see the launchd.plist man page for a complete list. A simple inetd service might look something like this:

<dict>
 <key>Disabled</key>
 <false/>
 <key>Label</key>
 <string>com.myorg.somejob</string>
 <key>Program</key>
 <string>/usr/local/sbin/somejob</string>
 <key>Sockets</key>
 <dict>
  <key>Listeners</key>
  <dict>
   <key>SockServiceName</key>
   <string>9999</string>
  </dict>
 </dict>
 <key>inetdCompatibility</key>
 <dict>
  <key>Wait</key>
  <false/>
 </dict>
</dict>

/usr/local/sbin/somejob will be called whenever there is a connection on port 9999, and you can interact with the socket by reading and writing STDIN/STDOUT as normal for inetd.