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Script that automatically switches between several configured time machine backup servers
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autotm is a system service (daemon) that manages multiple time machine backup destinations for you in a tranparent way. If you move between different locations where you want to maintain separate time machine backups, autotm is for you. I've written autotm for my own use and have been runing it since the first release on my MacBook.


  • Edit autotm.conf.sample to match your setup

  • Copy files:

    sudo cp autotm.rb /usr/local/bin/autotm

    sudo cp de.abstracture.autotm.plist /Library/LaunchDaemons/

    sudo cp autotm.conf.sample /etc/autotm.conf

    sudo chmod 0600 /etc/autotm.conf

  • Load the daemon (needs to be run only once):

    sudo launchctl load /Library/LaunchDaemons/de.abstracture.autotm.plist

Config file

The config file is in yaml format and contains configurations for available destinations using the following keys:

  • type (remote | local)
  • volume (only for local)
  • hostname (only for remote)
  • username (only for remote)
  • password (only for remote)
  • path (optional for remote, default is '/Backups')

The sample file should hopefully be self-explanatory with respect to file format.

Some notes regarding actual values:

Local destinations (essentially usb or firewire disks) only need one key: the path to the volume. This is typically "/Volume/<Volume Name>" where <Volume Name> is the volume's name as shown in the Finder. Note that you don't need to quote the name should it contain blanks. It will be handled automatically.

The default for the optional remote path is /Backups, which is what OSX Lion Server uses as a name for its time machine share. This may vary depending on your setup.

The easiest way to determine your backup configuration for remote backups is to grep through your system.log:

grep backupd /var/log/system.log | grep "Mounted network"

This will show you the used URL:

Sep 20 02:16:14 Thebe[92971]: Mounted network destination at mountpoint: /Volumes/Backups using URL: afp://jdoe@mymac.local/Backups

This would translate to:

  • type: remote
  • hostname: mymac.local
  • username: jdoe
  • path: /Backups

in your config file (where path is optional).

Bonjour Names

It is possible (most likely in the case of backup disks attached to AirPort base stations) that the URL you grep from the log file looks like:

21/11/2011 23:01:41.913 Mounted network destination at mountpoint: /Volumes/Western Digital 2Tb using URL: afp://dan@AirPort._afpovertcp._tcp.local/Western%20Digital%202Tb

In this case strip out the _afpovertcp._tcp part and simple enter AirPort.local as the server name. As the path, if it contains spaces, both Western%20Digital%202Tb and Western\ Digital\ 2Tb should work.

URL Escaping

If you are configuring autotm for local disks, no escaping of special characters should be required. In the case of remote destinations, the backup destination is specified by a URL and these have certain rules for escaping certain characters (see for example

This is true for all parts of the URL, most notably the password, which is sent as part of the URL but not printed to the autotm log file. If you are using any special characters, use the percent escape codes or prefix the character with a backslash ().


In order to monitor what autotm is doing, the LaunchDaemon is configured to log to /var/log/autotm.log. You can inspect this file through the console to confirm everything is working as expected.

Server Selection Logic

A few notes about how servers are selected:

  • autotm looks at your system.log to determine if the last backup failed
  • if it failed, autotm will go through the list of configured destinations to look for an alternative
  • multiple available destinations will get prioritized in the following order:
    • choose local destinations first (in order listed)
    • if multiple remote destinations are available (i.e. respond to pings), autotm will pick the fastest one (your office server may be visible via a presumably slower VPN connection for example but you want to avoid backing up there from home)
  • if your last backup was successful but the destination is not available anymore autotm will check for alternatives and pick the 'best' one, as described above
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