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- Singularity .img files
- Singularity images in registry via the shub:// protocol
- Docker images in registry via the docker:// protocol
- a tar archive, eventually bzipped or gzipped
- a folder
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Official images for official software may have already been prepared by the software group within your experiment and be available through a shared filesystem (such as CVMFS), SingularityHub or other supported repository. Please check with your software manager about the support to Singularity.
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A singularity recipe is a text file that contains all the instructions and configurations needed to build an image. It is organized in a header and a number of optional sections. The header is composed by a list of configuration settings in the form of "keyword: value" describing the system to use as base for the new image. Sections are identified by the % sign followed by a keyword. For a detailed list of all possible sections refer to [25].
An example of recipe file follows:
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NOTE: since building a new image requires root access on the host system, it will not be possible on CNAF computing resources.
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Singularity allows to run image-shipped software by simply prepending the singularity exec image.img text on the command line. The current working directory (CWD) is maintained and non-system files are available, so that, for example, the output of the ls command run in a container is not very different from the same command run natively.
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