LaunchD

Pointers

• http://developer.apple.com/documentation/MacOSX/Conceptual/BPSystemStartup/Articles/LaunchOnDemandDaemons.html
• /System/Library/LaunchDaemons/
• ~/Library/LaunchAgents/

Replaces

• init
• rc, the init.d and rc.d scripts
• SystemStarter
• inetd and xinetd
• atd
• crond
• watchdog

Lingon

• http://lingon.sourceforge.net/

Lingon is a graphical interface for creating launchd configuration files and controlling them through launchctl for Mac OS X Tiger... You get all your launchd configuration files listed in a table so you easily can see which are loaded and what they do, and you can also load and unload any easily. If you want to create or edit a launchd configuration file you can do that in Lingon through an assistant or in an easy graphical way (or through an built-in text editor, should you want to).

I generally prefer command line interface to gui, but lingon is an exception to the rule.

Command line

    launchctl unload ~/Library/LaunchDaemons/filename
    launchctl load ~/Library/LaunchDaemons/filename

    launchctl list

    launchctl start
    launchctl stop

How to

• http://www.macgeekery.com/tips/all_about_launchd_items_and_how_to_make_one_yourself

Example plist file

• launchd job specification should be saved in ~/Library/LaunchAgents as e.g. local.periodic.kick.plist

    <?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
    <plist version="1.0">
    <dict>
        <key>Label</key>
        <string>wu.nagios</string>
        <key>ProgramArguments</key>
        <array>
            <string>/usr/local/nagios/bin/nagios</string>
            <string>-d</string>
            <string>/usr/local/nagios/etc/nagios.cfg</string>
        </array>
        <key>OnDemand</key>
        <false/>
    </dict>
    </plist>

Apache

For processes that daemonize (e.g. apache), set the OnDemand key as illustrated above. You may need to manually start the service after booting, and the service will not automatically be restarted in the event that it dies.

Required behaviours

To support launchd, you must obey the following guidelines when writing your daemon code:

• You must provide a property list with some basic launch-on-demand criteria for your daemon. See "Creating a Launchd Property List File".
• You must not fork your process and have the parent process exit.
• You must not daemonize your process. Calling the daemon function makes launchd think your process has died and prevents it from relaunching your process if it really does die.

Although they are normally part of the daemon creation process, it is worth emphasizing that forking and exiting the parent process and calling the daemon function must be avoided if you want to support launchd. The launchd program configures your daemon to run as a daemon before your code is ever called, so these steps are unnecessary. In addition, calling them interferes with the ability of launchd to launch your daemon on demand.