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A Recovering Physicist: Time Machine won’t automatically back up after 10.6.4 *solved*

Time Machine won’t automatically back up after 10.6.4 *solved*

2010-07-05 17:50

[Update 2010-07-07] I got automatic TM backups working again, thanks to help from the Twitterverse, two private mailing lists, and an Apple discussion forum. Updates are at the bottom.

[Update 2010-07-14] Not completely working as it turns out.

[Update 2010-07-15] The timing (if not the cause) of the vanishing Automatic setting is determined.

Time Machine stopped doing automatic backups on my MacBook Pro, apparently when I updated to 10.6.4 on 2010-06-16.

Each time I enter System Preferences > Time Machine, the switch on the left says TM is OFF and the Next Backup time reads: Automatic backups off. I can turn the switch to ON (the word “ON” does not turn blue, as it should, and Next Backup does not change), but when I exit and re-enter, it shows OFF again.

Automatic backups do not happen. Backup only runs when I initiate it manually, or when the machine reconnects to the home network, after time away or upon reboot.

/Library/Preferences/com.apple.TimeMachine.plist when opened in Property List Editor says “AutoBackup, Boolean, [checkmark].”

I have dragged /Library/Preferences/com.apple.TimeMachine.plist out of its folder and restarted, letting TM recreate it, then re-connected to the backup volume and re-created my list of items to omit from backup. It didn’t change anything about the above behavior.

I looked in the backup set to see whether either

  /Applications/Time Machine.app

had been updated at 10.6.4. Indeed, both had changed:

component June 1 (before 10.6.4) July 5 (after 10.6.4)
/System/Library -
  /PreferencePanes -
  /TimeMachine.prefPane -
  /Contents/MacOS -
2010-03-02 628,256 2010-05-06 636,496
/Applications -
  /TimeMachine.app -
  /Contents/MacOS -
  /Time Machine
2009-09-01 51,008 2010-05-10 51,008

First I replaced the directory


from a June 1 backup. After reboot — nothing had changed.

Next I replaced the directory

  /Applications/Time Machine.app

from a June 1 backup. After reboot — nothing had changed.

Stumped. Ideas?

[Update 2010-07-07]

TM auto-backup is now working again. I believe the magic combination was (1) 10.6.4 combo update followed by (2) restoring /System/Library/LaunchDaemons/com.­apple.­backupd-auto.­plist from a backup before I could possibly have messed with it. (Some time before mid-June I had hand-edited this file to lengthen the interval between backups. Auto-backup continued to work on the longer interval until the first 10.6.4 update.)

In the TM preference panel, “ON” is now lit up blue. Backups happen every hour.

My takeaway from this investigation is best summed up by Chuck Goolsbee, who said this on a private list:

I've found TM to either be perfect, or perfectly awful. There seems to be no middle ground. It has saved me on three occasions. But I have also had machines where TM never worked. Odd errors. Unhelpful error messages. Hair-pulling frustrations. So my philosophy is: If it works, use it. If it so much as hiccups, switch to something else.

[Update 2010-07-14]

All is not quite back to normal. Now TM randomly forgets that it is set for automatic backups. Normally I become aware of this when I notice that the laptop hasn't been running hot for some time — it routinely goes to 160° F or more during backups. TM can be switched to automatic from the System Preference panel, and it will back up hourly until the next time it forgets, usually a day or less.

[Update 2010-07-15]

The pattern is now clear: each time I leave the home network with this laptop, and then return and reconnect, TM does an immediate backup but turns the Automatic switch to OFF.