airport-autojoin

TL;DR Summary: a [mac os x specific] shell script to automatically join Wi-Fi/AirPort networks

Details

I came across this question on AskDifferent and it reminded me that I had dealt with the same problem with one of my Macs awhile ago.

I dug out the shell script that I had written to "solve" the problem, and then (of course) decided to re-write it, even though I'm not having the problem now.

The idea is very simple:

• use the airport command[1] to check to see if we are connected to a Wi-Fi network:

  • If we are connected to a Wi-Fi network already, exit

  • If we are not connected to a Wi-Fi network, scan for local available networks.

• Compare available SSIDs against a list of "known SSIDs" (which you have to add to the script):

  • if none are available, exit
  • if one is available, try to join it using the networksetup command.

That's pretty much it.

launchd

This script can be called two ways:

1. directly through the command line.
2. via launchd which will automatically run it

Put the airport-autojoin.sh in /usr/local/bin/ and then install com.tjluoma.on-network-change.plist to /Library/LaunchDaemons (which will make sure that it is run as root).

Authentication

The shell script needs to run as root in order to run the networksetup command. If you run it via launchd as recommended above it will be run as root.

The firs time you run this script, you may be asked to authenticate with a message like this:

If so, just enter your login name and password.

Update 2014-11-13

com.tjluoma.joinwifi.plist is another attempt to solve this problem, but it doesn’t try to get very fancy about it, it just uses a straight up call to tell airport to join the strongest Wi-Fi network.

To use this, you only need to use the com.tjluoma.joinwifi.plist and if you use the other method, you do not need to use com.tjluoma.joinwifi.plist. Pick one.

Configure

Important! If your Wi-Fi port is not en0 (it may be en1 or something else, under odd circumstances) you must change this line in com.tjluoma.joinwifi.plist:

	<string>en0</string>

Install

Once you have that set correctly, save it to /Library/LaunchDaemons/com.tjluoma.joinwifi.plist and make sure that it is owned by root with the proper permissions.

Set Permissions:

chmod 644 /Library/LaunchDaemons/com.tjluoma.joinwifi.plist

Move file into place:

sudo mv -vn com.tjluoma.joinwifi.plist /Library/LaunchDaemons/com.tjluoma.joinwifi.plist

Change owner/group (required by launchd):

sudo chown root:wheel /Library/LaunchDaemons/com.tjluoma.joinwifi.plist

Load file into launchd

sudo launchctl load /Library/LaunchDaemons/com.tjluoma.joinwifi.plist

Uninstall

You can remove the file with two commands:

Remove it from launchd:

sudo launchctl unload /Library/LaunchDaemons/com.tjluoma.joinwifi.plist

Delete the launchd plist:

sudo /bin/rm /Library/LaunchDaemons/com.tjluoma.joinwifi.plist

Footnote

1. You know about the `airport` command, right? It's located at /System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport although I always link it to /usr/local/bin/airport as soon as I setup a new Mac. ↩