# Building Images

For more information regarding building a singularity container, the [Building a Container](https://singularity.lbl.gov/docs-build-container) documentation is excellent and we recommend becoming familiar with it.

{% hint style="info" %}
Container images can take up a lot of disk space. You may want to save them in a location with a large quota and it is also a good idea to change singularity's default cache directory ( i.e`~/.singularity)`to a location that gets cleaned up regularly i.e `~/.scratch`. In order to change the chache directory, you need to set the appropiate variable in your `~/.bashrc` file. For instance:

```bash
# set SINGULARITY_CACHEDIR. Make sure directory exists!
export SINGULARITY_CACHEDIR=~/scratch/.singularity
```

{% endhint %}

## From SingularityHub

You can use the `build` command to download a container from Singularity Hub.

```bash
singularity build <finalImageName>.simg shub://<singularityHubURL>
```

The first argument (`<finalImageName>.simg`) specifies a path and name for your container. The second argument (`shub://<singularityHubURL>`) gives the Singularity Hub URI from which to download.

{% hint style="info" %}
Note, you do not actually use the `<>` when entering your path/name or url.
{% endhint %}

## From DockerHub

If you already have a desired docker container that you would like to build as a singularity image for use on OSCAR, you can build directly from dockerHub using the build command:

```bash
singularity build <finalImageName>.simg docker://<dockerHubURL>
```

This will pull the docker image from DockerHub and build it as a singularity image locally.