How to convert Netcdf4 files to Netcdf3 files with NETCDF_nccopy

My system is Ubuntu 14.04, and netcdf-4.3.3.1has been installed

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root@xx-desktop:~/Desktop/cc# nccopy

nccopy: nccopy [-k kind] [-[3|4|6|7]] [-d n] [-s] [-c chunkspec] [-u] [-w] [-[v|V] varlist] [-[g|G] grplist] [-m n] [-h n] [-e n] [-r] infile outfile

[-k kind] specify kind of netCDF format for output file, default same as input

kind strings: 'classic', '64-bit offset',

'netCDF-4', 'netCDF-4 classic model'

[-3] netCDF classic output (same as -k 'classic')

[-6] 64-bit-offset output (same as -k '64-bit offset')

[-4] netCDF-4 output (same as -k 'netCDF-4')

[-7] netCDF-4-classic output (same as -k 'netCDF-4 classic model')

[-d n] set output deflation compression level, default same as input (0=none 9=max)

[-s] add shuffle option to deflation compression

[-c chunkspec] specify chunking for dimensions, e.g. "dim1/N1,dim2/N2,..."

[-u] convert unlimited dimensions to fixed-size dimensions in output copy

[-w] write whole output file from diskless netCDF on close

[-v var1,...] include data for only listed variables, but definitions for all variables

[-V var1,...] include definitions and data for only listed variables

[-g grp1,...] include data for only variables in listed groups, but all definitions

[-G grp1,...] include definitions and data only for variables in listed groups

[-m n] set size in bytes of copy buffer, default is 5000000 bytes

[-h n] set size in bytes of chunk_cache for chunked variables

[-e n] set number of elements that chunk_cache can hold

[-r] read whole input file into diskless file on open (classic or 64-bit offset format only)

infile name of netCDF input file

outfile name for netCDF output file

netCDF library version 4.3.3.1 of Nov 6 2015 20:09:00 $

root@xx-desktop:~/Desktop/cc# nccopy -k classic pres.nc pres3.nc

NetCDF: Unknown file format

Location: file nccopy.c; line 1354

root@xx-desktop:~/Desktop/cc#

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