For some reason, I can not longer complete a backup to a remote Time Machine server. In the error log, I see thousands of error messages. Here's generally what they look like:

2016-10-27 16:13:31.330679-0500 localhost mtmd[745]: (TimeMachine) [com.apple.TimeMachine.TMLogError] -[FileAttrs writeAttributesToItemAtPath:] setattrlist failed for path '/.MobileBackups/Computer/2016-10-27-161316/Volume/Library/Preferences' (errno 1)

The errors are slightly different only at the end (/.MobileBackups/Computer...)

Ultimately, the backup takes days before the connection to the server is reset for some reason and the backup fails to complete.

What are these errors and what do I need to do to fix this?


It may relate to this and/or help someone else figure out more about this but when I look at directories that are subject to the failure on my Mac, I see:

    sudo ls -al@ '/.MobileBackups/Computer/2016-11-05-233040/Volume/Library/'
    total 0
    d------r-x@ 4 root  wheel  136 Nov  5 23:33 .
        com.apple.backupdelta.MoveChecked     3 
        com.apple.s stem.Security    68
    drwxr-xr-x@ 5 root  wheel  170 Nov  5 23:30 ..
        com.apple.backupd.SnapshotVolumeFSEventStoreUUID     36 
        com.apple.backupd.SnapshotVolumeLastFSEventID    20 
        com.apple.backupd.SnapshotVolumeUUID     36 
    d------r-x  5 root  wheel  170 Nov  5 23:32 Application Support
    d------r-x@ 4 root  wheel  136 Nov  5 23:33 Preferences
        com.apple.backupdelta.MoveChecked     3

I imagine most of these file attributes are related to Time Machine's local backup process, but I also notice that one of the attributes is com.apple.s stem.Security .. note the blank character in the system path component. Could that be confusing things? For example, if that attribute was set with that typo and later cleared (or attempted to be) with it spelled correctly, you would see an error like this.

Just guessing ..


I don't have a definite answer yet either, but I'm basing my approach on bad content/permissions in the .MobileBackups subtree. Since these files store incremental backups in-between true Time Machine backups, I'm somewhat comfortable removing them and "starting fresh".

Viewing the logs:

Missing from the question is how to view the Time Machine logs. I installed a script in my /usr/local/bin directory, based on the answer here. However, a more straightforward command is simply:

log stream --style syslog --info --predicate 'processImagePath contains "backupd" and subsystem beginswith "com.apple.TimeMachine"'

Investigating Logged Errors

Inspecting the directories, there didn't seem to be much "off" about them (as @RamsayCons points out in his answer). Since I didn't care much about the most recent mobile backup, I decided to simply remove it:

sudo rm -rf /.MobileBackups/Computer/2016-12-16-112458

A few notes about this command:

  • Remember that with sudo comes great power. Please be sure you understand exactly what you are doing before continuing.
  • Similarly, rm -rf can cause great pain and anguish, so be sure that you are confident in what you are doing and have an exact directory specified.
  • use the command ls -la /.MobileBackups/Computer/ to list the contents of your existing Mobile Backups, so you can specify the correct

I am still waiting to see if this will resolve my problem, but so far I am seeing a new set of messages in the logs.

A few differences in my problem vs. that described:

  • I am backing up to a locally mounted drive, however, the problem seems rooted in the files stored in the /.MobileBackups/ directory, and not related to "where" the TimeMachine Backup disk is located
  • My errors include a message that volume Macintosh HD (/) is now in an emergency freespace condition, and low disk space thinning needed for volume Macintosh HD (/) with 7.7 <= 10.0 pct free space, despite having >40GB out of 230GB free.
  • My Backup never "failed", but sat in the "Preparing backup ..." status in System Preferences for over 18 hours.


My Time Machine Backup eventually completed during the next scheduled hourly run... Hooray!


The MobileBackups folder are used for the local Time Machine snapshots. I had the same problem after cloning (with CCC from Mike Bombich) a MacBook Pro.

Instead rm you can use:

sudo tmutil disablelocal
sudo tmutil enablelocal

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