I back up my Macbook Pro using Time Machine to OS X server at both work and home. Two different backups. The more the better, right? The only thing I didn’t like was having to switch the TM destination manually by going into System Preferences, Time Machine, etc. Lots of clicks. ”I need automagic”, I thought. After a lot of Googling, I came up with a way that works. Here’s how.
First off, you need to figure out how Time Machine remembers it’s backup destination. You can do this by running this command in the Terminal:
[sourcecode language=“bash”]defaults read /Library/Preferences/com.apple.TimeMachine BackupAlias[/sourcecode]
. That’ll output some really long string of characters. I have no idea what they mean, but that is how Time Machine remembers which disk/volume it is using. It’ll look something like this:
[sourcecode language=“bash”]00000000 03aa0002 00010642 61636b75 70000000 00000000 00000000 00000000 00000000 0000c79e f1f5482b 00010000 00010642 61636b75 70000000 00000000 00000000 …….. 00000668 65617476 34000018 00206166 703a2f2f 68656174 76344044 61727769 6e2e6c6f 63616c2f 4261636b 7570ffff 0000[/sourcecode]
. I cut my output short because it’s pretty long, but you’ll need your entire output from one < to the last >. You’ll need both of these strings of numbers for each Time Machine destination. The only way I know how to get them is to set it in Time Machine preferences first, then do the defaults read to get the value.
Once you have both, we’ll need to put each in it’s own respective shell script, like so:
defaults write /Library/Preferences/com.apple.TimeMachine BackupAlias ’00000000 03aa0002 00010642 61636b75 70000000 00000000 00000000 00000000 00000000 0000c79e f1f5482b 00010000 00010642 61636b75 70000000 00000000 00000000 …….. 00000668 65617476 34000018 00206166 703a2f2f 68656174 76344044 61727769 6e2e6c6f 63616c2f 4261636b 7570ffff 0000′[/sourcecode]
. So when you’re done you’ll have two different scripts. Make sure they’re executable by doing
[sourcecode language=“bash”]chmod +x script.sh[/sourcecode]
. After that, you can actually run them to verify it does change your Time Machine destination just by doing
, then going into Time Machine preferences and seeing what destination has been set. If it works, put both scripts somewhere out of the way and leave them there. I have a folder in my home directory
where I keep various Applescripts, so I put them there. They do not actually have to be in your user or system path ($PATH) based on how we’re setting it up, but it won’t hurt either way.
Now we’ve got the backend of switching Time Machine destinations set up, we need a way to trigger it. I wanted to do this based on my IP address, because my work IP address range is different from at home. To do this, I’m using MarcoPolo. It took me a while to figure out how MarcoPolo works, but it’s basically like this (assuming I understand it correctly):
- A “context” in MarcoPolo is basically a set of rules.
- Whatever “context” is active, only the rules that belong to it will be in effect.
Since I’m only using MarcoPolo for one purpose at this time, I only have one context, and two rules. This wasn’t evident to me at first, because I couldn’t figure out how to tell which rule would trigger which action. The best I can tell is that they’re in order… the first rule will trigger the first action, and so on. Not 100% clear on that yet.
So my first rule is for my home network, which only has one subnet, so it was easy to configure:
The second rule was for work, and based on my location between various buildings, my IP address could change quite a bit. I thought of making the rule specific to the subnet I’m on when I’m in my office, but I decided to go with the entire IP range:
After that, I set up the actions to correspond with the order of the rules:
I set the delay on the actions just to give the OS time to get settled with other network based events that might be going on. I’m sure you could do without it, I’m just weird that way.
So, this morning when I got to work, it didn’t work out for me because I was misunderstanding the purpose of contexts. I thought you had to have a different context for each rule. :( But I did verify that the tm_work.sh script did switch my Time Machine backup destination and I kicked off the backup manually, which worked fine.
When I got home after work, I got back online to see if MarcoPolo would do it’s magic. Sure enough, it did. I’ll watch it over the next few days to make sure it switches and backs up reliably, but this is looking to be a great way to have more than one Time Machine destination.