/usr/share/dune-grid/grids/dgf/cube-testgrid-2-2.dgf is in libdune-grid-dev 2.5.1-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 | DGF
VERTEX
0 0
0.5 0
1 0
0 0.5
0.3 0.6
1 0.5
0 1
0.5 1
1 1.2
#
CUBE
0 1 3 4
1 2 4 5
3 4 6 7
5 4 8 7
#
|