[netcdfgroup] Bug renaming coordinate variables or dimensions in netCDF-4 files

• To: NetCDF Group List <netcdfgroup@xxxxxxxxxxxxxxxx>
• Subject: [netcdfgroup] Bug renaming coordinate variables or dimensions in netCDF-4 files
• From: Russ Rew <russ@xxxxxxxx>
• Date: Tue, 18 Nov 2014 11:21:31 -0700

In recent versions of the netCDF-4 C library (versions 4.3.1, 4.3.2, and
release candidates of 4.3.3 before 4.3.3-rc3) there is a serious bug in
functions that attempt to rename either a coordinate dimension or its
associated coordinate variable in a netCDF-4 or netCDF-4 classic model
file. Other libraries and applications built on those versions of the
netCDF-4 C library inherit this bug. Fortunately, renaming a dimension or
coordinate variable is not a commonly used operation, which is one of the
reasons this bug was only discovered recently (October 2014). In netCDF-4
library versions before 4.3.1, an error indication is returned, so renaming
a coordinate dimension or variable isn't even possible.

In versions affected by the bug renaming appears to work as intended,
returning no error indication, but values of the associated coordinate
variable are silently replaced by fill values. The bug only occurs for
netCDF-4 files, including files using netCDF-4 classic model format.

If you have attempted to rename a coordinate variable or associated
dimension in place using one of the library versions affected by this bug,
we recommend checking the values of renamed coordinate variables, using
"ncdump -v variable_name", for example.

The upcoming version 4.3.3 will include a fix for this bug, as well as
comprehensive tests to make sure it won't re-occur as the result of future
updates. Our apologies for anyone affected by this bug, and thanks to
Charlie Zender for researching and reporting the bug. Charlie has
written informative
historical notes
<http://nco.sourceforge.net/nco.html#ncrename-netCDF-Renamer> about this
and previous netCDF-4 renaming bugs in documentation for the NCO ncrename
utility.

Again, please note that this bug only affects netCDF-4 files; netCDF-3
files are unaffected.

-- 
Russ Rew
UCAR Unidata Program