Does anyone know what’s the meaning and source of the following message?
WARNING: OpenMP support not enabled during compilation; using 1 thread only. (…/fix_omp.cpp:123)
A LAMMPS executable using USER-OMP package needs to have a compilation flag like -fopenmp during compilation and linking.
On macOS, the default compiler does not support this, and the two makefiles Makefile.serial and Makefile.mpi do not have these flags on by default.
The warning tells you that even though the package is installed, OpenMP is not enabled since these flags were not present during compilation.
Modify the makefile to include -fopenmp in both CCFLAGS and LINKFLAGS, do a full make clean-all and recompile.
If you are using a Mac, you need to use a compiler that supports OpenMP.
Anders
Dear Anders
I’m running on Ubuntu, so, what’s your idea on the warning?
Exactly what I wrote 
Modify the makefile to include -fopenmp in both CCFLAGS and LINKFLAGS, do a full make clean-all and recompile.
Anders