Apptainer: Difference between revisions

<b>NOTE:</b> Please note and heed the advice concerning building images/overlays given in section <b>[[#Building_images_or_overlays|Building images and overlays]]</b>.

Apptainer "images" can be created in the following formats:

* as a "sandbox" directory.

<code>SIF</code> files internally can contain multiple parts where each part is typically a squashfs filesystem (which are read-only and compressed). It is possible for <code>SIF</code> files to contain read-write filesystems and overlay images as well --but such is beyond the scope of this page: see the official Apptainer documentation on how to do such. Unless more advanced methods of building an "image" were used, the Apptainer <code>build</code> command produces a <code>SIF</code> file with a read-only squashfs filesystem when building images. (This is the preferred option since the resulting image remains as-is since it is read-only, and, the image is much smaller since it is compressed. Know that disk reads from that image are done very quickly.)

A "sandbox" directory is a normal directory in the filesystem that starts out as empty and as Apptainer builds the image it adds the files, etc. needed in the image to that directory. The contents of a "sandbox" directory should only be accessed, updated, etc. through the use of Apptainer. One might need to use a "sandbox" directory in situations where one needs to have read-write access to the image itself in order to be able to update the container image. That said, if updates are infrequent, it is typically easier and better to use an <code>SIF</code> and when updates need to be done, build a sandbox image from the <code>SIF</code> file, make the required changes, and then build a new <code>SIF</code> file, e.g.,