OS X Mountain Lion: If you don’t have permission to use a disk
If you don’t have permission to use the files on a disk that’s connected to your computer you can select an option to ignore ownership of files on the disk. When this option is selected, your computer treats all files on the disk as though they were owned by the current user, no matter who actually owns them.
This option is useful if you need to share the contents of an external disk among users at several different computers. It’s also helpful if you erased your startup disk and reinstalled OS X, because OS X creates a new user who may not be recognized as the user who “owns” the connected disk, even if the user has the same name that you used previously.
- Select the disk and choose File > Get Info.
- Click the disclosure triangle next to Sharing & Permissions to expand that section.
- Select the “Ignore ownership on this volume” checkbox.
This option doesn’t make all files accessible. If a file’s permissions don’t allow its owner to read from or write to it, the file remains inaccessible.
Do not select this option for a disk you plan to use to back up files, because user and group information may be lost.
If you are not the administrator of the computer, ask the computer’s administrator to give you access to the disk.
If you do not have permission to access items on a network, contact your system administrator to give you access.