How can I run a short MPI job using up to 4 nodes?

You can use SLURM Quality of Service (QOS) express by inserting the following line into your job script:

#SBATCH --qos=express

or using the option –qos with the sbatch command:

$ sbatch --qos=express <my_job_script>

The QOS has the following properties:

$ sacctmgr show qos express format=Name,Priority,MaxTres,MaxWall,Flags

      Name   Priority       MaxTRES     MaxWall                Flags
---------- ---------- ------------- ----------- --------------------
   express        100        node=4    00:20:00          DenyOnLimit

It is meant for short tests, debugging and similar uses and should not be used for repeated production runs.