Environment Variables

# Slurm Environment Variables

Variables set by Slurm inside job scripts and job steps.

## Most Commonly Used

| Variable | Description | Example |
|----------|-------------|---------|
| `SLURM_JOB_ID` | Job ID | `12345` |
| `SLURM_JOB_NAME` | Job name (`--job-name`) | `blast_run` |
| `SLURM_SUBMIT_DIR` | Directory where `sbatch` was run | `/home/jdoe/project` |
| `SLURM_NODELIST` | Allocated node(s) | `node[042-043]` |
| `SLURM_NTASKS` | Total tasks (`--ntasks`) | `32` |
| `SLURM_CPUS_PER_TASK` | CPUs per task (`--cpus-per-task`) | `8` |
| `SLURM_JOB_NUM_NODES` | Number of nodes | `2` |
| `SLURM_MEM_PER_NODE` | Memory per node in MB | `65536` |
| `SLURM_JOB_PARTITION` | Partition name | `batch` |
| `SLURM_JOB_ACCOUNT` | Account name | `smith_lab` |

## Job Array Variables

| Variable | Description | Example |
|----------|-------------|---------|
| `SLURM_ARRAY_JOB_ID` | Parent array job ID | `12340` |
| `SLURM_ARRAY_TASK_ID` | This task's index | `42` |
| `SLURM_ARRAY_TASK_COUNT` | Total tasks in array | `100` |
| `SLURM_ARRAY_TASK_MIN` | Lowest index | `1` |
| `SLURM_ARRAY_TASK_MAX` | Highest index | `100` |

## Node & Task Details

| Variable | Description | Example |
|----------|-------------|---------|
| `SLURMD_NODENAME` | Name of this compute node | `node042` |
| `SLURM_NODEID` | Node index (0-based) in allocation | `0` |
| `SLURM_PROCID` | MPI rank (global task ID) | `7` |
| `SLURM_LOCALID` | Local task ID on this node | `3` |
| `SLURM_NTASKS_PER_NODE` | Tasks per node | `16` |
| `SLURM_CPUS_ON_NODE` | CPUs on this node | `64` |
| `SLURM_NNODES` | Number of nodes in allocation | `4` |

## GPU Variables

| Variable | Description | Example |
|----------|-------------|---------|
| `SLURM_GPUS_ON_NODE` | GPUs allocated on this node | `2` |
| `CUDA_VISIBLE_DEVICES` | GPU device indices (set by Slurm cgroups) | `0,1` |
| `SLURM_JOB_GPUS` | GPU IDs allocated to job | `0,1` |

## Output Filename Patterns

Used in `--output` and `--error`:

| Pattern | Expands To | Example |
|---------|-----------|---------|
| `%j` | Job ID | `12345` |
| `%x` | Job name | `blast_run` |
| `%A` | Array job ID | `12340` |
| `%a` | Array task ID | `42` |
| `%N` | First node hostname | `node042` |
| `%u` | Username | `jdoe` |
| `%%` | Literal `%` | `%` |

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## References

- [SchedMD: sbatch -- Output Environment Variables](https://slurm.schedmd.com/sbatch.html#lbAF)
- [SchedMD: srun -- Environment Variables](https://slurm.schedmd.com/srun.html#lbAF)