It is possible to have a code snippet on how and when to call the parmetis package to partition the a mesh from a libmesh application code.
I've done like this after building a mesh object:
// Partition the mesh with ParMetis package.
pmetis.partition(mesh, 4); // Partition the mesh on 4 processors
// Print information about the mesh to the screen.
I get the following output which shows that I have only 1 subdomain:
So, what's wrong ?