15.1.2 File Handles
Each object on the NFS-mounted filesystem is referenced by a unique object called a file handle. A file handle is viewed by the client as being opaque?the client cannot interpret the contents. However, to the server, the contents have considerable meaning. The file handles uniquely identify every file and directory on the server computer.

The Unix NFS server stores three pieces of information inside each file handle.

Filesystem identifier
Refers to the partition containing the file (file identifiers such as inode numbers are usually unique only within a partition).

File identifier
Can be something as simple as an inode number, used to refer to a particular item on a partition.

Generation count
A number that is incremented each time a file is unlinked and recreated. The generation count ensures that when a client references a file on the server, that file is, in fact, the same file that the server thinks it is. Without a generation count, two clients accessing the same file on the same server could produce erroneous results if one client deleted the file and created a new file with the same inode number. The generation count prevents such situations from occurring: when the file is recreated, the generation number is incremented, and the second client gets an error message when it attempts to access the older, now nonexistent, file.

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