> ## Documentation Index
> Fetch the complete documentation index at: https://docs.nyc-ai.app/llms.txt
> Use this file to discover all available pages before exploring further.

# Software & modules

> Load compilers, MPI, and applications with the Lmod environment module system.

CUNY HPCC ships dozens of compilers, MPI libraries, math libraries, language runtimes, and applications. Rather than installing software system-wide in conflicting versions, the center uses **environment modules**. Each package is described by a module file that sets `PATH`, `LD_LIBRARY_PATH`, and related variables when loaded, and cleanly reverses those changes when unloaded.

<Info>
  HPCC uses **Lmod** (Lua-based, supports dependency hierarchies) to manage application environments. The commands below target Lmod; always check the login banner and `module avail` on the system you're using.
</Info>

## Core commands

| Command                   | What it does                                                                                            |
| ------------------------- | ------------------------------------------------------------------------------------------------------- |
| `module avail`            | List all modules visible with the currently loaded prerequisites.                                       |
| `module spider <name>`    | Search **all** modules (including those behind dependency chains) and show how to load them. LMOD only. |
| `module whatis <name>`    | Print a one-line description of a module.                                                               |
| `module load <name>`      | Load a module into the current shell.                                                                   |
| `module unload <name>`    | Unload a previously loaded module.                                                                      |
| `module list`             | Show everything currently loaded.                                                                       |
| `module purge`            | Unload everything.                                                                                      |
| `module swap <old> <new>` | Replace one loaded module with another.                                                                 |

## A typical workflow

Inspect what's loaded by default, then change it for your job:

```bash theme={null}
module list
# Currently Loaded Modules (example):
#   1) gcc/12.3.0    2) openmpi/4.1.5

module unload openmpi/4.1.5
module load openmpi/4.1.6
```

Search for a package and load a specific version:

```bash theme={null}
module spider python
module load Python/3.10.4
python3 -c "import sys; print(sys.version)"
```

Inside a SLURM script, load every module you need **before** launching your program, so compute nodes start with the right environment:

```bash theme={null}
#!/bin/bash
#SBATCH --job-name=python_job
#SBATCH --nodes=1
#SBATCH --ntasks=1
#SBATCH --time=00:30:00

module purge
module load Python/3.10.4
module load NETCDF/4.2.0      # example: NETCDF compiled with PGI

cd $SLURM_SUBMIT_DIR
python3 analysis.py
```

<Tip>
  Starting a script with `module purge` makes it reproducible. It doesn't matter what was loaded in the submitter's interactive shell.
</Tip>

## What's available

The module tree covers the usual HPC stack:

* **Compilers:** GNU, Intel / oneAPI, NVIDIA HPC SDK, and other system-specific toolchains.
* **MPI:** OpenMPI, Intel MPI, and other system-specific MPI builds.
* **Math / scientific libraries:** FFTW, NetCDF, HDF5, BLAS/LAPACK implementations.
* **Languages:** Python (multiple versions), Julia, R, Perl.
* **Applications:** MATLAB, and domain-specific codes as installed by HPCC staff.

The exact versions available evolve over time. Always check with `module avail` or `module spider` on the system you're using, not a memorized list.

## Requesting new software

If a package you need isn't installed, email the [HPC Helpline](mailto:HPCHelp@csi.cuny.edu) with:

* The software name and version you'd like.
* A link to its install instructions or source.
* Why you need it (a one-line justification is fine).

For personal Python or Julia environments, you can typically manage packages yourself inside your home directory. Use `python -m venv`, `conda env create`, or Julia's package manager.

## Compiling your own code

See the [Program Compilation](http://wiki.csi.cuny.edu/cunyhpc/index.php/Programcompilation) page on the HPCC Wiki for compiler flags and linker hints that work cleanly with the module tree.

## Next steps

<CardGroup cols={2}>
  <Card title="Submit a job" icon="play" href="/job-submission">
    Annotated SLURM templates that show where `module load` fits.
  </Card>

  <Card title="Storage & quotas" icon="database" href="/storage">
    Where to install your virtualenvs and Conda environments.
  </Card>
</CardGroup>