How do you run a script after a network interface comes up?

Question

Is there a way to run a script every time a network interface finishes coming up? Or, is there an equivilent answer to this Debian question on OSX?

Answer 1

I haven't tried this solution my self - yet, but found this thread: https://superuser.com/questions/201478/run-script-in-os-x-10-6-on-network-connection-like-etc-network-if-up-d/261004#261004

You should consider using crankd, which precisely allows you to run scripts in response to many system events such as network changes, filesystem activity, application launching, etc.

As I couldn't find any sensible documentation, I also wrote a small blog post on getting started using crankd.

Answer 2

The following works on Mac OS X 10.11.3 (El Capitan)

1. Create a file: networkchange.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>networkchange</string>
  <key>LowPriorityIO</key>
  <true/>
  <key>ProgramArguments</key>
  <array>
    <string>/Users/Shared/bin/networkchange.sh</string>
  </array>
  <key>WatchPaths</key>
  <array>
    <string>/etc/resolv.conf</string>
    <string>/var/run/resolv.conf</string>
    <string>/private/var/run/resolv.conf</string>
  </array>
  <key>RunAtLoad</key>
  <true/>
</dict>
</plist>

2. Then, register by running the following commands in Terminal:

launchctl load networkchange.plist
launchctl start networkchange

Note that the script is run by the user registering the plist.

Answer 3

A launchd agent watching /etc/resolv.conf, and two network related .plist files under /Library/Preferences/SystemConfiguration/ seems to work for me (in Mac OS X 10.8.4):

<?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>ifup.ddns</string>

  <key>LowPriorityIO</key>
  <true/>

  <key>ProgramArguments</key>
  <array>
    <string>/Users/Shared/bin/ddns-update.sh</string>
  </array>

  <key>WatchPaths</key>
  <array>
    <string>/etc/resolv.conf</string>
    <string>/Library/Preferences/SystemConfiguration/NetworkInterfaces.plist</string>
    <string>/Library/Preferences/SystemConfiguration/com.apple.airport.preferences.plist</string>
  </array>

  <key>RunAtLoad</key>
  <true/>
</dict>
</plist>

I had previously only used /etc/resolv.conf, but there were cases where that wasn't enough.

Answer 4

I've ended up with with this script:

#!/bin/bash

COUNTER=0
while [ $COUNTER -lt 10 ]; do
    let COUNTER=COUNTER+1

    # assign to test at each iteration otherwise the output won't be changed
    test=$(ifconfig -a inet 2>/dev/null | sed -n -e '/127.0.0.1/d' -e '/0.0.0.0/d' -e '/inet/p' | wc -l)

    if [ "${test}" -gt 0 ]; then
        # do the job here
       
        # exit the loop
        let COUNTER=COUNTER+10
        break
    fi

    # give a little time for a network to get up
    sleep 2
done

It checks a network 10 times and the network has 2*10 seconds to get up.