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How to get OS X to mount drives on boot rather than login and leave them mounted when you logout

Views: 44331
Votes: 12
Posted: 19 Nov, 2007

When you logout of Mac OS X or reboot (and have not logged in yet), all locally attached volumes are, by default, unmounted.  This includes FireWire , USB, and other attached drives.  If you use BRU to backup to these drives, then you may experience the Mac OS X mount problem that occurs with Apple systems. The Mac OS X mount problem has been reported to Apple several times since 2002 and it remains in the latest Snow Leopard builds.

To prevent the OS X mount problem from happening and provide the ability to mount your locally attached drives without logging in, or have OS X keep them mounted after a user has logged out of the system, open a Terminal window (the Terminal.app application can be found in the Applications -> Utilities folder - a shortcut to the Utilities folder is ⌘-SHIFT-U) and run the following command as a user with Administrative privileges:

sudo defaults write /Library/Preferences/SystemConfiguration/autodiskmount AutomountDisksWithoutUserLogin -bool true

That will instruct Mac OS X to mount any FireWire, USB, or other directly attached disk devices to the Mac OS X system without requiring you to login. By doing so, you have the ability to leave BRU LE, BRU Server , and BRU PE backup to disk devices on a schedule without the requirement of being logged in to the system.


We have been made aware of another method that can be used and there have been many reports that it works on Mac OS X Panther (10.3.X) as well as Tiger (10.4.x) and Leopard (10.5.X).  That method is as follows:

  1. 'cd' to the /Library -> Preferences -> SystemConfiguration folder by running the following command:
    cd /Library/Preferences/SystemConfiguration/
  2. Create a file named "autodiskmount.plist" by running the following command:
    sudo pico autodiskmount.plist
  3. Copy and paste the following into the PICO window:

    <xml version="1.0" encoding="UTF-8"?>
        <!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN"
        "http://www.apple.com/DTDs/PropertyList-1.0.dtd" />
        <plist version="1.0">
                 <true />
  4. Exit PICO by typeing [CTRL-X] then, when prompted at the bottom of the window to save, select "y" and then press [ENTER].

You're done!

This tells autodiskmount to mount all local volumes at startup regardless of whether they are potentially removable (or whether the user has logged in yet). Apple decided to mount (potentially) removable volumes only while a user was logged in at the GUI . Users were assuming that removable volumes got unmounted when they logged out, and were causing file system corruption by disconnecting them while they were still live mounted file systems.  This also means that when you need to disconnected the external drive for any reason, you need to login and dismount the drive first to ensure a proper and safe removal to prevent corruption on your drive.

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