Ttgjyuk

following these guidelines MpichClusterUbuntu, I'm trying to execute my very first mpi program with a PC with Ubuntu 18.04.01 Server Edition and a laptop with Ubuntu 18.04.02 Desktop. Till step 11 of this guideline, everything went fine, with no problems at all.

I set up a machinefile called hosts
with these two lines:

192.168.1.7 # first 'master' node: the PC
192.168.1.5 # second node: the laptop

After compiling the very simple example file contained in the guidelines without:

#include <stdio.h>
#include <mpi.h>

int main(int argc, char** argv) 
 int myrank, nprocs;

 MPI_Init(&argc, &argv);
 MPI_Comm_size(MPI_COMM_WORLD, &nprocs);
 MPI_Comm_rank(MPI_COMM_WORLD, &myrank);

 printf("Hello from processor %d of %dn", myrank, nprocs);
 MPI_Finalize();
 return 0;


mpiu@pc01:~$ mpicc mpi_hello.c -o mpi_hello

Executing without considering the machinefile 'hosts', this is the output:

mpiu@pc01:~$ mpiexec -n 8 ./mpi_hello
------------------------------------------------------------------
[[27419,1],0]: A high-performance Open MPI point-to-point messaging 
module was unable to find any relevant network interfaces:

Module: OpenFabrics (openib)
 Host: pc01

Another transport will be used instead, although this may result in
lower performance.

NOTE: You can disable this warning by setting the MCA parameter
btl_base_warn_component_unused to 0.
----------------------------------------------------------------
Hello from processor 1 of 8
Hello from processor 2 of 8
Hello from processor 5 of 8
Hello from processor 6 of 8
Hello from processor 0 of 8
Hello from processor 3 of 8
Hello from processor 7 of 8
Hello from processor 4 of 8
[pc01:25010] 7 more processes have sent help message help-mpi-btl-
base.txt / btl:no-nics
[pc01:25010] Set MCA parameter "orte_base_help_aggregate" to 0 to see all
help / error messages

And when executing calling the machinefile 'hosts', the execution remains idle without producing any output:

mpiu@pc01:~$ mpiexec -n 8 -machinefile hosts ./mpi_hello

What am I missing? What am I doing wrong?
Looking forward to your kind help.
Marco

PS:
this is the content of /etc/netplan/50-cloud-init.yaml in the "master" node (PC):

network:
 ethernets:
 enp3s0:
 #addresses: []
 #dhcp4: true
 addresses: [192.168.1.7/24]
 gateway4: 192.168.1.1
 nameservers:
 addresses: [8.8.8.8,8.8.4.4]
 dhcp4: no
 version: 2