apptainer clean temp files

docs/source/user_guide/containers.rst

@@ -13,6 +13,18 @@ Commands can be run from within a container using the `apptainer run <https://ap
 
 If you encounter ``$HOME`` quota issues with Apptainer caching in ``~/.apptainer``, the environment variable ``APPTAINER_CACHEDIR`` can be used to select a different location such as a directory under ``/scratch``. See also, `apptainer build environment <https://apptainer.org/docs/user/main/build_env.html>`_
 
+Temporary Files
+~~~~~~~~~~~~~~~~~~~
+Apptainer creates temporary files its local /tmp directory.  Users occasionally encounter problems building images with apptainer when the /tmp space on a compute node (which is finite) filling up, which results in this error message: 
+
+.. code-block::
+
+   FATAL:   While performing build: while creating squashfs: create command
+   failed: exit status 1:
+   Write failed because No space left on device
+
+If apptainer fails in this way, run the command ``rm rf /tmp/build-temp*`` to remove apptainer's temporary files.  
+
 Your ``$HOME`` is automatically available from containers run via Apptainer. 
 You can ``pip3 install --user`` against a container's python, setup virtual environments, or similar while using a containerized application. 
 Just run the container's ``/bin/bash`` to get an Apptainer> prompt (or use ``apptainer shell <container>`` for a quick look from a login node).