Schedule TM to backup only on specific network

Question

Hi there .
How can i schedule my TM to backup only if I'm connected to a specific wireless network.
Because I'm using Time Capsule I want to TC make backups if I'm only connected to this wireless network and no other networks, because it's useless starting backup when I'm not connected to my TC network.

Answer 1

We ARE golden!
Here's a procedure that works to exclude some folders for any user, and to limit TM to be active only under certain conditions. Please read along.
Here's some information I wanted to share with the Mac community, on how to tweak Apple's Time Machine backup technology. Out of the box, TM is very easy to use (click and forget), but it heavily lacks configurable options, which leads to problems or at least 'challenges' in a corporate environment.
A lot of this info comes from stuff I found through Google, but a comprehensive guide with all info in 1 place does not seem to exist. So here I go. Grab a coffee and sit back.
Case
Our company wanted to test TM technology. I've set up a Mac OS X Server with a dedicated shared volume for the TM backups. The same principle is applicable to the Time Vault device. I'm NOT talking about TM with locally attached storage.
*Problem 1 - Exclusions*
The TM System Preference Pane offers only some very basic configuration options: Auto backup On/Off, Destination volume, Exclusions under the Option button, all of which are NON-enduser configurable. You need to be admin to change anything, which is good in a corporate environment.
Exclusions are a good thing. You don't want to back up generic files (ie. System, Apps), nor private user data (such as Movies, iTunes Music, Pictures). TM, however, offers no support to exclude these folders for every users of a system. You'd need to log in as an admin to every Mac and add these folders manually for every user. If another user logs into the system, this process needs to be repeated.
Can't we work with wildcards, so these folders are excluded for every user of the system?
*Problem 2 - Scheduling*
All runs fine when the Mac clients are on the LAN. TM will kick in every hour and start doing its job. There is plenty bandwidth available (wired or wifi) for TM to read indexes, copy data and do its meticulous checking. Believe me, TM is bandwidth-hungry! I've seen totals of 300MB of data going up and down for a delta backup of only 50MB 'real' fresh data.
On the LAN, all is OK, one just needs to have a little patience. The problem starts when users are not in the office, but connected to our VPN. Bandwidth is usually much lower (especially if connected through a 3G mobile service). Nevertheless, every hour TM will try and connect to the TM server, it will find it, but it will take a very long time for it to finish. Moreover, a lot of people have limited monthly data volumes, and TM will use this up rapidly.
The user doesn't have admin privileges, so (s)he can't deactivate TM in its System Preference pane. The running backup can be stopped manually, but this leads to ever-increasing backup times as more index checking needs to be done.
Apple 'forgot' to build in some scheduling or other checking mechanism (like location). As long as it can find the TM server, it will try to backup every hour.
Completely disabling auto-backup altogether defies TM's purpose, as users tend to forget launching backups manually.
Let's see what we can do here...
Solutions
Crippled as the TM GUI appears on its surface, there's plenty to play with under the hood. Here's what you'll need to follow along.
- root access
- familiarity with the Terminal and shell scripting
- notions of how terminal commands "defaults", "launchd" and "launchctl" work
- a .plist editor, i.e. Property List Editor.app (installed with XCode tools)
*Solution 1 - Exclusions*
The easy stuff first. There is a file
/System/Library/CoreServices/backupd.bundle/Contents/Resources/StdExclusions.pli st
which we open with Property List Editor.app.
You will see 3 keys: <ContentsExcluded>, <PathsExcluded> and <UserPathsExcluded>.
I've added extra strings under the <UserPathsExcluded> Array: "Downloads", "Movies", "Pictures", "Music" and some more. While you are at it, peek around in the other keys to see what never gets backed up.
That's it! For every user, these folders will be excluded once you've updated the StdExclusions.plist file. This will not be visible from the System Preferences, so warn your folks that they should look after their private stuff themselves.
*Solution 2 - Scheduling*
Aaah, here it gets interesting. As explained, an ordinary enduser has no control over the TM scheduling (basically switching it on or off) from the System Preference, as you need admin privileges to change this. How can we make TM only become active when on the company LAN?
There is a file
/System/Library/LaunchDaemons/com.apple.backupd-auto.plist
which actually schedules the hourly TM backup. Nothing interesting here, just good to know what drives TM. You could change the TM auto-backup frequency here, but that's not our goal. We would like to load/unload this plist completely to allow/prevent TM from activating.
Using launchctl, (please Google for more in-depth info on how launchd and launchctl work, it kinda replaces cron), this can be done easily with the command
+sudo launchctl unload /System/Library/LaunchDaemons/com.apple.backupd-auto.plist+
+sudo launchctl load /System/Library/LaunchDaemons/com.apple.backupd-auto.plist+
Another file is equally interesting:
/Library/Preferences/com.apple.TimeMachine.plist
which has a key <AutoBackup>. Its boolean and corresponds to the On/Off switch in TM System Preferences.
We want to switch it off automatically when not on the LAN, and on again when on the LAN.
Using the command defaults, this flag can be switched easily:
+defaults write /Library/Preferences/com.apple.TimeMachine AutoBackup -boolean no+
+defaults write /Library/Preferences/com.apple.TimeMachine AutoBackup -boolean yes+
Now let's bring these two together and AUTOMATE them. What we'll need is some kind of script that checks a condition (I've taken ifconfig listing a company IP address or not) and then executes above commands for us.
The script (I've saved it in /Applications/Time\ Machine\ Check/timemachinecheck.sh) reads like this:
#!/bin/sh
+check=`ifconfig | grep "inet <first 2 digits of company IP range>" | wc -l`+
+flagfile=/Applications/Time\ Machine\ Check/Time\ Machine\ Check\ OK.txt+
+if [ "$check" -eq 0 ] ; then+
+if [ -f "$flagfile" ] ; then+
+rm -f "$flagfile"+
+defaults write /Library/Preferences/com.apple.TimeMachine AutoBackup -boolean no+
+launchctl unload /System/Library/LaunchDaemons/com.apple.backupd-auto.plist+
fi
else
+if [ ! -f "$flagfile" ] ; then+
+date > $flagfile+
+defaults write /Library/Preferences/com.apple.TimeMachine AutoBackup -boolean yes+
+launchctl load /System/Library/LaunchDaemons/com.apple.backupd-auto.plist+
fi
fi
It's a simple script. You can adapt it to incorporate your own 'check'.
If a valid IP is found through ifconfig, the defaults and launchctl commands do their work. A flagfile is created as well, to stop this script from repeating the same commands and logging a system log entry every time it runs (which would not be a problem, but I like to keep my system.log tidy).
If no valid IP is found, defaults and launchctl shut stuff down. The flagfile is removed (so the script doesn't repeat its commands, see system log above).
OK, but how to schedule this script so it runs, say, every minute?
One creates a plist in
/Library/LaunchDaemons/com.tbwa.timemachinecheck.plist
which reads like this
+<?xml version="1.0" encoding="UTF-8"?>+
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">+
+<plist version="1.0">+
<dict>
<key>Label</key>
<string>com.yourcompany.timemachinecheck</string>
<key>OnDemand</key>
<true/>
<key>ProgramArguments</key>
<array>
+<string>/Applications/Time Machine Check/timemachinecheck.sh</string>+
</array>
<key>StartInterval</key>
<integer>60</integer>
</dict>
</plist>
Basically, all it does is run the timemachinecheck.sh script above every 60 seconds. As it is in /Library, this happens as root. As it is in /Library/LaunchDaemons, it is always active (as opposed to LaunchAgents which are only active once, when a user logs in)
Conclusion
This works for me. The nice thing is that although the auto-backup is disabled automatically when not on the company LAN, a user connected over VPN (on wide enough broadband) can still launch a backup manually.
I had wished this guide to be a little nicer on the eyes, but all the important info is here. You may need to brush up on the techie stuff, but there's the Internet and Google for that.