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Time Machine 10.8 – Part 3 – Advanced Features

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Hi, the command “defaults write /Library/Preferences/com.apple.TimeMachine MaxSize 102400” returns the message “defaults[1643:707] Could not write domain /Library/Preferences/com.apple.TimeMachine; exiting”. Should there be a “.plist” at the end of “com.apple.TimeMachine”? Thanks.


Hi Raj.
Most ‘defaults write’ commands require the action to be executed by the ‘Root’ user of your OS. This error is simply just warning you that you do not have permission to execute this command with the user you are logged in as. Simply enter ‘sudo’ before the rest of the command :
‘sudo defaults write /Library/Preferences/com.apple.TimeMachine MaxSize 102400’

Luis Rueda

I have changed the schedule with the sudo defaults write /System/Library/LaunchDaemons/com.apple.backupd-auto StartInterval -int 86400 command to make it run every day. However the “Next backup” keeps showing it will run in an hour. Any ideas on what might be missing? I’m running OS X 10.8.4

Hi Luis.
It seems somewhere in an update to 10.8 the StartInterval key was renamed BackupInterval within a launchEvents key of the com.apple.backupd-auto.plist file.
The quickest way to achieve your goal will be to download Textwrangler, XCode or any other Text editor of your choice and open the /System/Library/LaunchDaemons/com.apple.backupd-auto.plist with this application.
You can then modify the ‘Backup Interval’ integer key to ‘86400’.
Hope this sorts this out for you, ive just tested this on my machine fine!


Hi Russ,
Thanks for this information. Your website is the first place I have found ‘MaxSize’ mentioned as a way to set a fixed size for Time Machine backups. Most other advice seems to be to use a ‘hack’ which involves creating a fixed size Sparse Bundle and placing onto the Time Capsule disk.
Your method seems much better, so I’m surprised so many people are using the Sparse Bundle hack…
Any ideas why this might be? Is the ‘MaxSize’ option new or just not very well known?

Hi Matt, thanks for the feedback.
To answer your question, the answer is yes to both! The ‘MaxSize’ key setting is rather new, but also isn’t very well documented as is most advanced features on the mac. I think this is because Apple prefer people not tamper with default settings! 🙂
You can usually investigate the .plist files for most tweaks, its just a matter of finding the correct plist file and finding the correct key value!


This guide in its entirety is very helpful, thanks!
In trying to find a way to limit the backup size on a locally attached (USB) drive, I previously came across and applied the MaxSize solution.
sudo defaults write /Library/Preferences/com.apple.TimeMachine MaxSize
Unfortunately, although the key and string are shown correctly in the .plist, TM studiously ignores the value and keeps on filling up the drive to the max. This is on 10.8.4. Any suggestions?
Thanks again, -oliver

Hi Oliver, glad you have found this useful!
Providing the command is correct and the plist file shows the correct key and string value, on restart of the machine the next backup should apply these values.
All i can advise is that you ensure the command was successfully entered, restart the machine, maybe reselect the backup drive again in Time Machine preferences and give that a go.
Failing that, If all you need to do is limit the size of the backups to something less than the volume size, you could just create a partition on your USB drive of the size you require and set Time Machine to backup to this partition.


Thanks for the response. I may actually not have restarted the system since setting this up 🙁 so will give that a try first.


if i limit the size to let say 500gb, via
sudo defaults write /Library/Preferences/com.apple.TimeMachine MaxSize 512000
and i run more then one macbook do i have to enter this on each laptop or is this saved somehow on the time capsule?

Hi thorsten.
This is a system preference for the computer, not for the Time Capsule, so you will indeed need to apply this to each macbook.
To simplify this method, a Mobile Device Management solution (http://www.amsys.co.uk/tag/mdm/) could be used or you can configure this option within the Time Machine service on an OS X Server if you have a mac server.
But without a server, you just need to run this command on each machine.

I am wondering what would happen with a setting of *less* than an hour. How would TM manage to keep 1 back up every hour for the first 24 hours ? Has anybody ever tried that ?

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