Install the libsuitesparse-metis-3.1.0 and libsuitesparse-dev packages. In Ubuntu 9.10 (Karmic) or newer you can use the Synaptic package manager for that, or type:
sudo apt-get install libsuitesparse-metis-3.1.0 libsuitesparse-dev
Now go to the directory with Hermes. Create the file CMake.vars with the following lines (or append to the existing one):
set(WITH_UMFPACK YES)
and execute:
rm CMakeCache.txt
cmake .
make
Find more about Using UMFPACK in Hermes.
After the installation has been completed, you may select SOLVER_UMFPACK as the matrix solver for your finite element problems:
HermesCommonApi.set_integral_param_value(matrixSolverType, SOLVER_UMFPACK);