Apptainer vs crun
Apptainer
apptainer.orgcrun
github.comSide by side
| Figure | Apptainer | crun |
|---|---|---|
| Price from | Free | Free |
| Free plan | Yes | Yes |
| Free trial | — | — |
| Open source | — | — |
| Windows | Yes | — |
| macOS | Yes | — |
| Linux | Yes | Yes |
| API | Yes | — |
| Self-hosted | Yes | Yes |
| Plans published | 1 | 1 |
| Spec score · Container Engines | 8.9 (#1) | 8.5 (#5) |
| Spec score · Container Runtime Software | 8.9 (#1) | 8.6 (#3) |
| OCI compatibility | Apptainer can import containers from OCI registries and aims for compatibility with Docker containers. | crun conforms to the OCI Container Runtime specifications. |
| Purpose | Apptainer creates and runs containers that package software for portability and reproducibility. | crun is a fast, low-memory-footprint OCI container runtime written in C. |
| Security reporting | The Technical Steering Committee manages project security, and the policy directs vulnerability reports through private contact with the project. | The security policy directs vulnerability reports through GitHub Security Advisories rather than public issues or pull requests. |
| Security response | The Apptainer Technical Steering Committee accepts vulnerability reports at [email protected] and documents vulnerabilities through CVEs. | The project aims to acknowledge security reports within three business days and says confirmed issues are handled according to severity and impact. |
Plans
In their own words
Apptainer
Apptainer is a free container platform for creating and running portable, reproducible workloads, with a focus on shared systems and high-performance computing. It packages containers as immutable, single-file Singularity Image Format (SIF) images designed for transport and sharing. By default, users retain the same privileges inside and outside containers. Images can be signed and verified with PGP keys, PEM keys or X.509 certificates, and encrypted containers can run without writing decrypted contents to disk. Apptainer imports containers from OCI registries and aims to support most Docker Hub containers without changes. It can expose host resources such as GPUs, high-speed networks and parallel filesystems, and supports NVIDIA CUDA, AMD ROCm, Intel Gaudi and OCI Container Device Interface accelerators. Running Apptainer requires Linux; Windows and macOS need a Linux virtual machine, with Windows also listed via WSL2. Root access is unnecessary when user namespaces are available. Full functionality requires kernel support for FUSE and unprivileged user namespaces. Community support includes Slack, Google Groups and GitHub, with commercial services through CIQ.
crun
crun is a free, self-hosted OCI container runtime for Linux, written in C. It conforms to the OCI Container Runtime specifications and provides CLI operations for creating, running, executing commands in, listing, pausing, resuming, updating, checkpointing and restoring containers. It can generate a configuration for unprivileged use and creates a user namespace when run by a non-root user. The project documents integration with Podman, an Ansible role for installing a statically linked binary and a Lua binding. Build instructions cover Fedora, RHEL/CentOS Stream 9 and 10, Ubuntu, Alpine and openSUSE Tumbleweed; release binaries are listed for Linux amd64 and arm64, including variants without systemd. Official release artifacts are signed, with GPG verification commands provided. The project reports a benchmark of 100 sequential `/bin/true` containers completing in 1.69 seconds with crun versus 3.34 seconds with runc on the author's machine. The manual marks cgroup v1 support as deprecated. Regular patch releases target the latest version; fixes for earlier versions are best effort and not guaranteed.