What’s New in SingularityCE 4.1

This section highlights important changes in SingularityCE 4.1 that are of note to system administrators. See also the “What’s New” section in the User Guide for user-facing changes.

If you are upgrading from a 3.x version of SingularityCE we recommend also reviewing the “What’s New” section for 4.0.


  • SingularityCE will now build OCI-SIF images from Dockerfiles, if the --oci flag is used with the build command. Dockerfile builds are performed by buildkitd. If a buildkitd instance is not running on the host, SingularityCE will use its own customized ephemeral singularity-buildkitd. To disable the customized ephemeral buildkitd, remove libexec/singularity/bin/singularity-buildkitd, or remove execute permissions from this binary.

  • A new --keep-layers flag, for the pull and run/shell/exec/instance start commands, allows individual layers to be preserved when an OCI-SIF image is created from an OCI source. Multi layer OCI-SIF images can be run with SingularityCE 4.1 and later, and are not supported with earlier versions.


  • fuse2fs is required to mount legacy extfs container images via FUSE when kernel extfs mounts are disabled or unavailable. If fuse2fs is not available, SingularityCE will fall back to extracting containers to a temporary sandbox directory for execution.

  • Kernel 4.18 or above is required for Dockerfile builds. EL 7 does not support Dockerfile builds, and continues to have limited support for other OCI-mode features. SLES 12 has no support for OCI-Mode, including Dockerfile builds.

  • SingularityCE 4.1 is the final version that will support EL 7 and SLES 12. The mainstream end-of-life dates for these distributions are 2024-06-30 and 2024-10-31 respectively.


  • The sif fuse option in singularity.conf, which previously enabled experimental FUSE mounts of container images in some execution flows, is deprecated. When kernel mounts are disabled or unavailable, SingularityCE 4.1 now uses FUSE by default, with fall-back to extraction to a temporary sandbox directory.

  • A new tmp sandbox option in singularity.conf can be used to disable fall-back extraction of container images to temporary sandbox directories when kernel or FUSE mounts are unavailable. This option may be useful to avoid excessive filesystem load from implicit extraction of very large container images.