• Login node — where you type ssh into. Shared by everyone. No heavy compute here.
• Compute nodes — what Slurm hands out when you submit a job. Your work runs here.
• Slurm — the scheduler. You write a script that says how much and for how long, and it finds you a slot.

The loop we will practise: submit → check → read output. Repeat until you get what you want.

#!/bin/bash
#SBATCH --job-name=hello_world
#SBATCH --output=hello_world.out
#SBATCH --ntasks=1
#SBATCH --cpus-per-task=1
#SBATCH --time=00:01:00

echo "Job ID: ${SLURM_JOB_ID}"
echo "Host:   $(hostname)"
date
free -h
lscpu
env | sort > hello_world_${HOSTNAME}.env

• #SBATCH lines are comments to the shell, directives to Slurm
• Below the directives is just bash — anything you can run interactively
• Think reproducibility: the script documents exactly how the job was set up — do not rely on modules you loaded earlier or files you happened to have in $PWD; put everything the job needs inside the script

srun --ntasks=1 --cpus-per-task=1 --time=00:10:00 --pty bash

Lands you on a compute node with a prompt. Run the same commands you would put in a batch script.

• Quick checks: “does this module load cleanly?”, “does my script find its data?”
• Short-lived: exit when you are done — do not idle
• Some workflows genuinely need interactivity: steering a solver, inspecting intermediate results, manually nudging a parameter to escape a local minimum. If your science requires a human in the loop, this is the tool.

The point is not “never use interactive jobs” — it is use resources responsibly. Idle allocations block others. Batch is better when there is no human in the loop.

Inspect the reservation and QOS before you use them:

scontrol show res exeter-workshop-260421
sacctmgr show qos brics.e6c_qos

On the command line:

sbatch --reservation=exeter-workshop-260421 --qos=brics.e6c_qos sbatch_hello_world.sh

Or inside your batch script (add these two #SBATCH lines):

#SBATCH --reservation=exeter-workshop-260421
#SBATCH --qos=brics.e6c_qos

Gotchas:

• Reservation alone — works fine
• Reservation and QOS — works fine
• QOS without reservation — sbatch: error: Batch job submission failed: Invalid qos specification
• More than 2 nodes — QOSMaxNodePerUserLimit (the reservation caps per-user node count)

• ex01 ex01_hello_world/ → 01-hello-world.md — first sbatch submission
• ex02 ex02_multi_task/ → 02-multi-task.md — ntasks + srun + sacct
• ex03 ex03_interactive/ → 03-interactive.md — interactive shell
• ex04 ex04_matmul/ → 04-matmul.md — compile + run (build first: bash make.sh)

Each .md has the commands to run, questions to think about, and things to try if you finish early.