/usr/share/gromacs/top/charmm27.ff/rna.n.tdb is in gromacs-data 2018.1-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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[ 5' ]
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P
O1P
O2P
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O5' O5' ON5 15.9994 -0.66
C5' C5' CN8B 12.011 0.05
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1 2 H5T O5' C5' C4'
HN5 1.008 0.43 -1
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