Time Machine automatic backups fail, manual backups succeed

Short Description

Automatic Time Machine backups fail (with an error code of '19'), but manual backups succeed. Does anyone know what would cause this behavior?

Long Description & Troubleshooting Recon

On OSX v10.8.4, I've set up Time Machine to write backups to a network-attached storage (NAS) device. When Time Machine attempts to execute an automatic backup, it fails with the following error (appearing in system.log):

Sep  5 10:03:26 shaun-macmini.local com.apple.backupd[17870]: Starting automatic backup
Sep  5 10:03:26 shaun-macmini.local com.apple.backupd[17870]: Backup failed with error: 19

If I go into Time Machine settings, right click on the drive icon above the "Select Disk..." icon, and choose "Back Up Now", the backup succeeds:

Sep  5 10:21:06 shaun-macmini.local com.apple.backupd[17955]: Disk image /Volumes/BA_Backup/local’s Mac mini.sparsebundle mounted at: /Volumes/Time Machine Backups
Sep  5 10:21:06 shaun-macmini.local com.apple.backupd[17955]: Backing up to: /Volumes/Time Machine Backups/Backups.backupdb
Sep  5 10:21:07 shaun-macmini.local com.apple.backupd[17955]: Using file event preflight for Macintosh HD
Sep  5 10:21:10 shaun-macmini.local com.apple.backupd[17955]: Will copy (24.7 MB) from Macintosh HD
Sep  5 10:21:10 shaun-macmini.local com.apple.backupd[17955]: Found 10645 files (230.8 MB) needing backup
Sep  5 10:21:10 shaun-macmini.local com.apple.backupd[17955]: 1.31 GB required (including padding), 3.59 TB available
Sep  5 10:22:06 shaun-macmini.local com.apple.backupd[17955]: Copied 16396 files (173 MB) from volume Macintosh HD.
Sep  5 10:22:06 shaun-macmini.local com.apple.backupd[17955]: Using file event preflight for Macintosh HD
Sep  5 10:22:06 shaun-macmini.local com.apple.backupd[17955]: Will copy (442 KB) from Macintosh HD
Sep  5 10:22:06 shaun-macmini.local com.apple.backupd[17955]: Found 23 files (442 KB) needing backup
Sep  5 10:22:06 shaun-macmini.local com.apple.backupd[17955]: 1.04 GB required (including padding), 3.59 TB available
Sep  5 10:22:11 shaun-macmini.local com.apple.backupd[17955]: Copied 461 files (2.6 MB) from volume Macintosh HD.
Sep  5 10:22:11 shaun-macmini.local com.apple.backupd[17955]: Created new backup: 2013-09-05-102211
Sep  5 10:22:12 shaun-macmini.local com.apple.backupd[17955]: Starting post-backup thinning
Sep  5 10:22:12 shaun-macmini.local com.apple.backupd[17955]: No post-back up thinning needed: no expired backups exist
Sep  5 10:22:12 shaun-macmini.local com.apple.backupd[17955]: Backup completed successfully.
Sep  5 10:22:12 shaun-macmini.local com.apple.backupd[17955]: Ejected Time Machine disk image: /Volumes/BA_Backup/local’s Mac mini.sparsebundle
Sep  5 10:22:13 shaun-macmini.local com.apple.backupd[17955]: Ejected Time Machine network volume.

Subsequent automatic backups still fail, however everytime I've executed one manually, I have no issues.

Research into whatever the cause of "error 19" is hasn't revealed anything useful so far. Most advice on the Apple forums ranges from resetting the Time Machine backup to replacing the NAS device. Since the manual backup succeeds, that would seem to indicate some issue with the NAS mount. The manual backups seem to both mount and unmount the NAS device (or so says the logs), but the automatic backups do not appear to do the same thing.

I tried adding the mount of the NAS device to my user's "Login Items" and re-establishing the mount, but that does not appear to resolve the issue, either.

If I right-click the Time Machine icon in the top menu and select "Back Up Now", I get an error that the backup disk is not available. However, I can immediately go into the preference pane as described earlier and invoke a successful backup there.

What's causing my automatic backups to fail?

Solution 1:

Not a real answer, more a workaround to have your backups automatically despite this bug. That worked for me (see this answer of my own question).

Open a command line and say tmutil destinationinfo. Copy the ID you see in the ID line (a long suite of alphanumerical characters and -'s).

Now type tmutil startbackup -d TheID replacing TheID by the ID you just noted before (so something like tmutil startbackup -d 11326F32-D5BA-4FE8-83FB-E9CBD8F6FF2D but with an other ID). Open Time Machine Preferences and check if the backup is running. You may have to wait a few seconds before you see anything.

If that works, you can add it to your crontab so it is automatically run manually every hour (sounds contradictory?). Type crontab -e on the command line to edit your cron jobs, and add the following line in it:

0 * * * * tmutil startbackup -d TheID

again replacing TheID by the ID of your backup. Next hour check if anything is happening. You can replace the leading 0 by the minute you want it to be run.