Problems of mpirun for OpenMPI - fortran

Question

I installed openmpi-4.0.0 (https://www.open-mpi.org/software/ompi/v4.0/) as follow
./configure --prefix="/usr/local/openmpi"
make
sudo make install
export PATH=$PATH:/usr/local/openmpi/bin
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/local/openmpi/lib/
source ~/.bashrc
sudo ldconfig
then enter the examples folder in the package, and use command:
make
mpirun -n 4 ./hello_usempi
it shows:
Hello, world, I am 0 of 1: Open MPI v2.1.1, package: Open MPI buildd#lcy01-amd64-009 Distribution, ident: 2.1.1, repo rev: v2.1.0-100-ga2fdb5b, May 10, 2017
Hello, world, I am 0 of 1: Open MPI v2.1.1, package: Open MPI buildd#lcy01-amd64-009 Distribution, ident: 2.1.1, repo rev: v2.1.0-100-ga2fdb5b, May 10, 2017
Hello, world, I am 0 of 1: Open MPI v2.1.1, package: Open MPI buildd#lcy01-amd64-009 Distribution, ident: 2.1.1, repo rev: v2.1.0-100-ga2fdb5b, May 10, 2017
Hello, world, I am 0 of 1: Open MPI v2.1.1, package: Open MPI buildd#lcy01-amd64-009 Distribution, ident: 2.1.1, repo rev: v2.1.0-100-ga2fdb5b, May 10, 2017
The problem seems to be only one processor is activated. Note, both openmpi-4.0.0 and Ifort were installed on my computer. Could anyone please give me a hand, thanks very much.
I add the messages of the command mpif90 -v and mpirun -v here
mpif90 -v
Using built-in specs.
COLLECT_GCC=/usr/bin/gfortran
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/7/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 7.3.0-27ubuntu1~18.04' --with-bugurl=file:///usr/share/doc/gcc-7/README.Bugs --enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ --prefix=/usr --with-gcc-major-version-only --program-suffix=-7 --program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-vtable-verify --enable-libmpx --enable-plugin --enable-default-pie --with-system-zlib --with-target-system-zlib --enable-objc-gc=auto --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-offload-targets=nvptx-none --without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
mpirun -v
[mpiexec#tony-ThinkPad-P50] set_default_values (../../ui/mpich/utils.c:3178): no executable provided
[mpiexec#tony-ThinkPad-P50] HYD_uii_mpx_get_parameters (../../ui/mpich/utils.c:3620): setting default values failed
[mpiexec#tony-ThinkPad-P50] main (../../ui/mpich/mpiexec.c:438): error parsing parameters
The code is here (Copyright of Open MPI https://www.open-mpi.org/software/ompi/v4.0/)
! Copyright (c) 2004-2006 The Trustees of Indiana University and Indiana
! University Research and Technology
! Corporation. All rights reserved.
! Copyright (c) 2004-2005 The Regents of the University of California.
! All rights reserved.
! Copyright (c) 2006-2015 Cisco Systems, Inc. All rights reserved.
! $COPYRIGHT$
!
! Sample MPI "hello world" application using the Fortran mpi module
! bindings.
program main
use mpi
implicit none
integer :: ierr, rank, size, len
character(len=MPI_MAX_LIBRARY_VERSION_STRING) :: version
call MPI_INIT(ierr)
call MPI_COMM_RANK(MPI_COMM_WORLD, rank, ierr)
call MPI_COMM_SIZE(MPI_COMM_WORLD, size, ierr)
call MPI_GET_LIBRARY_VERSION(version, len, ierr)
write(*, '("Hello, world, I am ", i2, " of ", i2, ": ", a)') &
rank, size, version
call MPI_FINALIZE(ierr)
end
The contents of the makefile are quite long, I think it is not convenient to post here, it is still in the install package of OpenMPI-4.0.0. Thank you once more.