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What are ACL's

If you have no idea what an ACL's is then you should read up on them at Wikipedia. In summary, “an access control list (ACL) is a list of permissions attached to an object.”

Mac OS X ACL Support

If ACL's are supported by your version of Mac OS X and your version of rsync then it is recommended that you enable ACL support on the backup volume.

  • Please note that on Mac OS 10.6 and later ACL's are typically enabled on all volumes which offer ACL support and the command listed below “fsaclctl” is not available.

ACL Commands

The fsaclctl tool on Mac OS X is used to enable and disable ACL's on a volumes. A couple of examples are listed below for reference purposes. Replacing the '/' with '/Volumes/VolumeName' will allow you to check or specify the ACL status on a volume other than the root volume.

  • Determine the ACL’s status of the root volume :
 % /usr/sbin/fsaclctl -p /

  • Enable ACL’s on the root volume :
 % sudo /usr/sbin/fsaclctl -p / -e

  • Disable ACL’s on the root volume :
 % sudo /usr/sbin/fsaclctl -p / -d

  • fsaclctl command overview : The -p option allows you to specify a file system mount point path on which you wish to either enable or disable ACL’s. If no other options are specified then the access control list status will be displayed when using the -p option. Further details are available from the man page.

ACL Support on Different Versions of MAC OS X

  • Mac OS 10.6.X : On Mac OS Snow Leopard systems ACL's are on and there is no fsaclctl command available.
  • Mac OS 10.5.x : On Mac OS Leopard systems the ACL's are enabled by default.
  • Mac OS 10.4.x : By default ACL's are not enabled on Mac OS Tiger systems. If you are running Mac OS 10.4 then it is recommended that ACLS's are enabled on the backup destination volume. ACLs may be enabled or disabled on a per volume basis.
  • Mac OS 10.3.x and Earlier : ACL's are not supported on Mac OS X 10.3.9 or later. If you need to preserve Mac OS X meta data then it is recommended that you use rsync version 3 and Mac OS 10.4.11.

Editing Extended Attributes on MAC OS X

Under certain circumstances may wish to edit extended attributes. In order to edit extended attributes on Mac OS X, you may use a tool called 'xattr'. Help for this tool is available via the terminal. Open a terminal and then enter the line below and a help page for the tool will be displayed.

  • xattr -h

Disabling the backup of ACL's

It is possible to disable the backup of ACL's on darwin by adding the following to your configuration file :

# Disable ACL preservation, only availible on darwin with custom rsync (YES/NO)
 disable_acl_preservation="YES" # (If enabled ACL's will not be preserved in the backup)

Other Mac OS X Volume Configuration Options

It is important to ensure that the permissions for a backup volume are enabled.

Helpful Links