/usr/lib/ is in libplplot-dev 5.9.9-2ubuntu2.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/fortran/include/plplot/
/usr/lib/libplplotqtd.so
/usr/lib/libplplotf77cd.so
/usr/lib/fortran/
/usr/lib/fortran/include/
/usr/lib/fortran/include/plplot/plplot_parameters.h
/usr/lib/fortran/modules/
/usr/lib/fortran/modules/plplot/
/usr/lib/fortran/modules/plplot/plplot.mod
/usr/lib/fortran/modules/plplot/plplotp.mod
/usr/lib/fortran/modules/plplot/plplot_flt.mod
/usr/lib/pkgconfig/
/usr/lib/pkgconfig/plplotd.pc
/usr/lib/pkgconfig/plplotd-c++.pc
/usr/lib/pkgconfig/plplotd-f77.pc
/usr/lib/pkgconfig/plplotd-f95.pc
/usr/lib/pkgconfig/plplotd-tcl.pc
/usr/lib/pkgconfig/plplotd-wxwidgets.pc
/usr/lib/pkgconfig/plplotd-ada.pc
/usr/lib/pkgconfig/plplotd-d.pc
/usr/lib/pkgconfig/plplotd-ocaml.pc
/usr/lib/pkgconfig/plplotd-qt.pc
/usr/lib/libplplotwxwidgetsd.so
/usr/lib/libcsirocsa.so
/usr/lib/libcsironn.so
/usr/lib/libplplotcxxd.so
/usr/lib/libplplotd.so
/usr/lib/libplplotf77d.so
/usr/lib/libplplotf95cd.so
/usr/lib/libplplotf95d.so