Cannot access files on external drives

Many users have experienced problems reading files stored on external or networked drives.

Many users have experienced problems reading files stored on external or networked drives.

Apple Discussions poster dafoxman writes:

"After migration of G5 system from cloned drive some of my folders in the New user account had permission problems. Somehow I wound up with the Lock icon on my 2nd internal drive and 3 of my external drives. I tried the Get Info, won't correct the problem and let me change permissions so I can access them. Error: The folder "driveName" could not be opened because you do not have sufficient privileges."

MacFixIt has reported on similar problems, with users not able to search the files on external drives, or not being able to delete files marked as "locked" on the external drives.

There are several reasons why a user would not be allowed to access files on a shared resource such as an external drive; for instance, if there is a permissions problem with the files. However, it is also possible the drive could be formatted with a filesystem that has file attributes enabled which are not supported by OS X. One example of this is file locks in the FAT format which are not supported in OS X.

The first thing users should do if they cannot access files is check the format of the external volume. To do this, either right-click and "Get Info" on the volume, or get information on the volume in "Disk Utility". If the volume was formatted on the macintosh then most likely it is formatted to HFS (Mac OS Extended), but also could be FAT if users purchased it as a "Windows and Mac" compatible drive. If the drive has been used on a windows machine, it is possible the "File Locks" or other attributes could have been enabled, which would prevent users from accessing the files in OS X.

If the drive was originally used on a Windows machine, it could be formatted to NTFS. While OS X does support reading from this format, it does not support writing to it. This should not affect users as long as they have access to the files on the drive, but if there is a permissions error then users would have no way of correcting the problem on the Mac. If the drive is formatted to HFS , then it is more than likely this is just a permissions problem and users should easily be able to fix it.


Access files on FAT or NTFS formatted drives on Windows PC If the drive is non-HFS and users are having permissions problems then it is most likely a problem that can be solved best with access to a Windows PC. If users can resolve file locks on FAT drives or change the permissions of problematic files on NTFS drives, then the file should be accessible on the Mac. However, if worse comes to worse users should be able to copy the files to the PC and then format the drive properly. This might be required for problems with FAT-formatted drives, and it is recommended to use the Macintosh to format the drive to HFS (Mac OS Extended) to ensure full compatibility with the Mac, provided the drive will be used on the Mac.

Force permissions changes on the drive in the Terminal If the drive is formatted to HFS and is just having permissions problems, then users can ensure all files on the drive are accessible with the following set of terminal commands.

First change the ownership of the file to the current user and group.

sudo chown -R `id -un`:`id -gn` /Volumes/"DRIVE_NAME"

Second, remove all ACLs for the files on the drive.

chmod -RN /Volumes/"DRIVE_NAME"

Lastly, ensure the current user/group has full read and write access to the files.

chmod 775 /Volumes/"DRIVE_NAME"

In these commands, "DRIVE_NAME" is the name of the drive as it appears in the Finder. In addition, these commands are recommended for use only on external drives, since modifying file permissions on the boot drive can lead to problematic behavior. OS X's "Disk Utility" might be able to change permissions back to their defaults for system files, but it is best to avoid having to do this.

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