It is possible that two or more utilities or programs could be accessing the same file at the same time, making changes. For example, two people could be using ed to edit the same file at the same time. When a file has been accessed by more than one user simultaneously, the last changes saved overwrite any previous changes.

In a program, you can use byte-range locking to avoid this problem. For more information about byte-range locking in a program, see z/OS XL C/C++ Programming Guide.

You can use the Network File System feature to coordinate locking of remote files and directories. See Using the Network File System feature for an overview of this feature. For more detailed information, consult the appropriate Network File System documentation.