MPI Jobs

MPI jobs run a single program across multiple processes, potentially spanning several nodes. Use the Tasks and Tasks per node fields to configure the MPI layout.
Fields to set
Field
sbatch equivalent
When to use
Nodes
--nodes
Number of nodes to allocate.
Tasks
--ntasks
Total MPI process count across all nodes.
Tasks per node
--ntasks-per-node
MPI processes per node. Use instead of Tasks when you want even distribution.
CPUs per task
--cpus-per-task
Threads per MPI process. Set to 1 for pure MPI; higher for hybrid MPI+OpenMP.
Example — pure MPI, 4 nodes × 32 tasks
module load openmpi/openmpi-5.0.7-rocky9-slurm
cd $HOME/myproject
mpirun ./simulate --config config.yaml
Set Nodes to 
4, Tasks per node to 
32, CPUs per task to 
1. Do not pass 
-n to 
mpirun — Slurm passes the process count automatically via PMI.
Example — hybrid MPI + OpenMP
module load openmpi/openmpi-5.0.7-rocky9-slurm
export OMP_NUM_THREADS=$SLURM_CPUS_PER_TASK
cd $HOME/myproject
mpirun ./simulate --config config.yaml
Set Tasks per node to the number of MPI ranks per node, and CPUs per task to the number of OpenMP threads. The product of the two should not exceed the node's core count.
Choosing a partition
MPI jobs that span nodes require a partition with inter-node connectivity. Check with HPC support if you are unsure which partition to use for multi-node jobs.