# How to use CUDARequirement?

**URL:** <https://cwl.discourse.group/t/how-to-use-cudarequirement/861>\
**Category:** CWL Questions\
**Created:** [January 4, 2024, 1:51pm UTC](https://cwl.discourse.group/t/how-to-use-cudarequirement/861 "2024-01-04T13:51:33Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![marveso](https://yyz2.discourse-cdn.com/free1/user_avatar/cwl.discourse.group/marveso/32/492_2.png) [@marveso](https://cwl.discourse.group/u/marveso)\
**Post date:** [January 4, 2024, 1:51pm UTC](https://cwl.discourse.group/t/how-to-use-cudarequirement/861/1 "2024-01-04T13:51:33Z")

</div>

Hello guys, I’d appreciate if you could help me out with assigning a GPU to a docker container within CWL. I’ve been searching how to do this for hours, but I couldn’t manage to make it work…

I’m trying to use the `cwltool.CUDARequirement` extension in my CWL specification, but once I execute the workflow, I get the following error that is tied to the CUDARequirement requirement:

```auto
Field 'class' contains undefined reference to 
'http://commonwl.org/cwltool#CUDARequirement'

```

This is the implementation of said requirement:

```auto
requirements:
  cwltool:CUDARequirement:
    cudaVersionMin: "11.4"
    cudaComputeCapability: "3.0"
    cudaDeviceCountMin: 1
    cudaDeviceCountMax: 8

```

And here’s the specified namespace:

```auto
$namespaces:
  cwltool: "http://commonwl.org/cwltool#"

```

I wonder whether that URL is still valid as if you do go to the [http://commonwl.org/cwltool#CUDARequirement](http://commonwl.org/cwltool#CUDARequirement) you will notice that actually it doesn’t really lead anywhere.

* * *

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**For reproducibility purposes** , here’s a simple example of an a CWL CommandLineTool specification ( **example.cwl** ) that uses `cwltool:CUDARequirement`, yet it still throws the same error.

```auto
cwlVersion: v1.2
class: CommandLineTool

requirements:
  InitialWorkDirRequirement:
    listing: 
    - $(inputs.scriptFile)
  DockerRequirement:
    dockerPull: docker.io/pytorch/pytorch
  NetworkAccess:
    networkAccess: true
  cwltool:CUDARequirement:
    cudaComputeCapabilityMin: '3.0'
    cudaDeviceCountMax: 8
    cudaDeviceCountMin: 1
    cudaVersionMin: '11.4'

stdout: output.txt

inputs:
  scriptFile:
    type: File
    default:
      class: File
      path: script.py
    inputBinding:
      position: 1

outputs:
  stdout_output:
    type: stdout

baseCommand: "python"

$namespaces:
  cwltool: "http://commonwl.org/cwltool#"

```

The contents of **script.py** :

```auto
import torch

if __name__ == " __main__":
    print("CUDA AVAILABLE:", torch.cuda.is_available())

```

I use `cwltool` as a CWL runner. In other words, to execute this specification, I perform the following command: `cwltool example.cwl`.

* * *

* * *

If you know of any other method how to access and utilize the host GPU devices in docker container within the CWL, feel free to share them.

Thank you for your assistance, in advance.

---

<div class="post-metadata">

**Author:** ![mrc](https://yyz2.discourse-cdn.com/free1/user_avatar/cwl.discourse.group/mrc/32/3_2.png) [@mrc](https://cwl.discourse.group/u/mrc)\
**Post date:** [January 4, 2024, 6:43pm UTC](https://cwl.discourse.group/t/how-to-use-cudarequirement/861/2 "2024-01-04T18:43:37Z")

</div>

Welcome @marveso ; which CWL runner do you use? For example, the CWL reference runner requires the `--enable-ext` flag to use extensions.

---

<div class="post-metadata">

**Author:** ![marveso](https://yyz2.discourse-cdn.com/free1/user_avatar/cwl.discourse.group/marveso/32/492_2.png) [@marveso](https://cwl.discourse.group/u/marveso)\
**Post date:** [January 8, 2024, 9:20am UTC](https://cwl.discourse.group/t/how-to-use-cudarequirement/861/3 "2024-01-08T09:20:35Z")

</div>

Hey, thanks for the help, I didn’t know that flag was necessary, even though it wasn’t the only thing to fix though.

Luckily, I’ve finally found out what the issue was. Besides cwltool, I’ve also installed in my environment REANA, that downgraded my cwltool version to `3.1.2021xxxx` version that apparently doesn’t support the said extension, hence the errors. After upgrading the cwltool to a current version, it worked.

In other words, I had to:

- upgrade cwltool to the current version (as of this moment, the current version was `3.1.20231207110929`)
- use `--enable-ext` flag when executing the workflow