Allocate a single core

msub -I

Allocate four cores on 1 node

msub -l nodes=1:ppn=4 -I

Allocate five cores on multiple node

msub -l nodes=5 -I

Allocate three cores on three node

msub -l nodes=3:ppn=1 -I

In most cases, you don't want to specify the topology (the exact number of processors per node). If you let MOAB choose the topology for you, your job might run sooner. If there are not enough nodes available to run an interactive job immediately or if the topology you picked is not available, you will have to wait!