Testing for a Network Volume

Q:  How can I reliably determine if a volume is mounted over the network?

A: There are numerous ways to test whether a volume is a network volume. The best method to use depends on the layer that you're working at:

• If you're working on general application code, you should use NSURL for this. Construct a URL for any item on the volume and then call -getResourceValue:forKey:error: to get the NSURLVolumeIsLocalKey key; the returned value will be false (kCFBooleanFalse) for a network volume and true (kCFBooleanTrue) for a local volume.

• If you're programming at the BSD layer, you can call statfs and test the MNT_LOCAL flag in the f_flags field that it returns. Alternatively, you can call getattrlist to request the ATTR_VOL_MOUNTFLAGS attribute, which can be more efficient than statfs under some circumstances.

One word of warning here: the distinction between network volumes and local volumes is somewhat blurry these days. For example, you can't assume that network volumes are slow, or that local volumes don't have to deal with file locking issues. In general you should test for the existence of specific functionality rather than making assumptions based on the volume type. For example, you can use the NSURLVolumeSupportsAdvisoryFileLockingKey key to determine whether a volume supports advisory locking.

Document Revision History