Setting persistent interface options not availible in preferences.

Question

Hello,
I'm looking for the proper place (file(s) to edit) to add customized network interface options which will be applied at boot up and anytime there are network location (kicker) change.
I need to assign en0 a non default metric upon system boot and any time the interface may be reset. I can do this with "ifconfig en0 metric 100" but am looking for where I can automate this without requiring the client to type it in each time it is required.
All machines are 10.5.x or 10.6.x.
Thanks for your help,
greg

Answer 1

Insofar as system boot is concerned, you could create a launchd.plist file to do this and put it in /Library/LaunchDaemons/. Here is a draft plist that might do this -- in other words, I copied one of mine and made a couple of quick text edits so this may or may not work. But it should get you going down the right path.
<?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>metric</string>
<key>Disabled</key>
<false/>
<key>ProgramArguments</key>
<array>
<string>/sbin/ifconfig</string>
<string>en0</string>
<string>metric</string>
<string>100</string>
</array>
<key>RunAtLoad</key>
<true/>
</dict>
</plist>
You may be able to use something like the "watchpaths" key if something in a file or directory someplace changes when the interface may be reset. That would add another key like
<key>WatchPaths</key>
<array>
<string>/path/to/file/or/directory/to/watch</string>
</array>
Do a man launchd and man launchd.plist to read more about how to create launchd jobs. Also, look at how Apple has done some of theirs: /System/Library/LaunchDaemons/com.apple.periodic-daily.plist, for example.