/usr/share/gmt/custom/square.def is in gmt-common 5.3.1+dfsg-2.
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 | # $Id: square.def 12822 2014-01-31 23:39:56Z remko $
#
# Definition file for square symbol. Use in psxy
# as -Sksquare/size. Unlike -Ss this allows for
# using patterns as fill
#
-0.353553391 0.353553391 M
0.353553391 0.353553391 D
0.353553391 -0.353553391 D
-0.353553391 -0.353553391 D
|