If the mount fails, check with your system administrator to ensure that you are authorized to access the MVS data sets or z/OS UNIX files and that the data sets or files are listed in the exports data set. The privilege level required to enter mount and umount commands varies among client operating system implementations. Many UNIX implementations limit these commands to the root user or superuser mode. If the MVS system operator issues the freeze=on operand of the z/OS NFS server modify command, all new tries to mount an MVS or z/OS UNIX file system fail until the z/OS system operator issues the freeze=off operand. If the z/OS system operator issues the freeze=onhfs operand of the z/OS NFS server modify command, z/OS conventional MVS data sets can still be mounted, but all new tries to mount z/OS UNIX file systems fail until the system operator issues the freeze=offhfs operand.