Mac OS X v10.6: Using MS-DOS (FAT32)-formatted disks for home directories

With the introduction of Mac OS X v10.6 Snow Leopard, you can use MS-DOS (FAT32)-formatted disks, including USB flash drives or external hard drives, to store external accounts or home directories. However, you should be aware of some things if you use a home directory on an MS-DOS formatted disk.

This article has been archived and is no longer updated by Apple.

If you need to keep a home directory on a MS-DOS-formatted disk, be aware that:

  • The MS-DOS (FAT32) file system format does not support permissions, file owners, and groups. Such permissions are synthesized on Mac OS X with some default permissions. Because of this all files will have the same permissions, which include having the execute bit being set. This means that files with an unregistered extension appear as "Unix Executable Files" in the Finder, with a Terminal-like icon.
  • SSH private keys will be publicly readable; this will cause SSH to display warning messages.
  • Files on MS-DOS (FAT32) file systems are limited to a size of 4 GB. This may affect applications which use very large files, such as video editing software.
  • Extended attributes are stored as AppleDouble files. While these files are marked as hidden, if the disk is connected to a Microsoft Windows system which ignores the hidden attribute, these files may be displayed or inadvertently deleted by a user. Extended attributes are used by many Mac applications (resource forks and Spotlight metadata are stored as extended attributes.)
  • Applications and features that track file IDs may not behave as expected. File IDs are a native attribute for Mac OS Extended (Journaled) volumes but must be synthesized for MS-DOS file systems; these may change based on updates to the file.

Apple recommends using Mac OS X Extended (Journaled) formatting for disks with home directories. You can reformat disks in Disk Utility, in the Utilities folder.

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