Mac OS X launchd

Daemons have become pretty confusing on Mac OS X. Originally these were handled by inetd, then xinetd, and now launchd has taken over. Unfortunately, there's a mess of left over stuff hanging around: you'll still find services in /etc/xinet.d and other places.

No longer true as of Snow Leopard. You don't have an xinetd.d directory and although you may still have leftover rc.common and rc.netboot files, they are bnot used. Launchd has taken over.

The goal of launchd is to replace xinetd, cron, and anything you might have stuck in rc.local or StartupItems. It controls system programs, but it can be used for ordinary user processes also.

Anything you want controlled by launchd needs a plist file describing what to do if you want it to start automatically, but you can use it to daemonize a specific command also:

 $ launchd  -d -- ~/bin/ltest 
 
 

However, by using configuration files, you can use "launchctl" to more powerfully control your jobs. There's an interactive mode - if you just type "launchctl" you can then control daemons from its shell:

launchd% list
com.apple.KernelEventAgent
com.apple.mDNSResponder
com.apple.nibindd
com.apple.periodic-daily
com.apple.periodic-monthly
com.apple.periodic-weekly
com.apple.portmap
com.apple.syslogd
com.vix.cron
org.postfix.master
org.xinetd.xinetd
com.kerio.watchkms
launchd% 
 

See tftp and launchctl on MacOSX for an example of using launchct.

Read more about launchd at http://developer.apple.com/macosx/launchd.html and see the man pages for launchd and launchctl for details. You can see system launchd plist files in /System/Library/LaunchDaemons/; use these to understand how you'd write your own.

3 comments

More Articles by Tony Lawrence - Find me on Google+ 2005-12-01

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Fri Jun 2 13:46:08 2006: 2065   bruceg2004


I'm not sure I like launchd. Apple seems to be the only vendor using it (please correct me, if I am wrong). I pefer xinetd, since many applications take advatage of it. Does launchd use hosts.allow and hosts.deny?

- Bruce



Fri Jun 2 20:54:41 2006: 2066   TonyLawrence


But launchd is much more than xinetd. See http://www.afp548.com/article.php?story=20050620071558293



Sun Jun 4 02:04:55 2006: 2067   bruceg2004


Once again, Tony; you have helped me see the light. Excellent link, and very good information on launchd. Now I need to study up, and learn it. I think what I should have said, was that I am lazy, and it was always easy to add a static route in rc.local, rather then write some XML in a plist file :-)

Thanks again, Tony.

- Bruce





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