I have been compiling FeNICS for RHEL6. Trilinos is a collection of linear algebra and equation solvers. Are all of them required? Or just specifc ones?
As Jan answered, Trilinos is optional.
If you want to enable Trilinos, then Epetra, ML, Ifpack and Amesos are required.
Trilinos is optional as well as PETSc which is default linear algebra backend.