| name | crun-1-27-0 |
| description | Lightweight OCI container runtime written in C for running Linux containers with low memory footprint and high performance. Use when deploying containers via podman, building container orchestration tools, checkpointing/restoring containers with CRIU, running WebAssembly workloads, or needing faster container startup than runc provides. |
| version | 0.1.0 |
| author | Tangled <noreply@tangledgroup.com> |
| license | MIT |
| tags | ["oci-runtime","containers","podman","checkpointing","criu","wasi","webassembly","cgroups"] |
| category | devops |
| external_references | ["https://github.com/containers/crun","https://github.com/containers/crun/blob/main/Documentation/crun.md"] |
crun 1.27
Overview
crun is a fast and lightweight OCI container runtime fully written in C. It conforms to the OCI Container Runtime Specification and is designed as a lower-level alternative to runc (which is written in Go). crun can also be used as a library (libcrun) that can be embedded directly into programs without requiring an external process for managing OCI containers.
crun is significantly faster than runc and has a much lower memory footprint. Benchmarks show approximately 50% faster container startup times (100 sequential /bin/true runs: 1.69s vs 3.34s). Its low resource usage allows running containers under extremely tight memory limits — as low as 512KB where runc fails at 4MB.
When to Use
- Running containers via Podman (crun is the default runtime on many distributions)
- Needing faster container startup and lower memory overhead than runc
- Checkpointing and restoring containers with CRIU (live migration, state preservation)
- Running WebAssembly/WASI workloads natively inside containers
- Building container orchestration tools that embed
libcrun directly
- Deploying containers in resource-constrained environments (edge, embedded)
- Working with cgroup v2 systems requiring automatic v1-to-v2 conversion
Core Concepts
OCI Runtime: crun implements the OCI runtime specification, meaning it works with any OCI-compliant bundle (a directory containing config.json and a root filesystem). It is interoperable with container managers like Podman, CRI-O, and containerd.
C-based Architecture: Unlike runc which is written in Go and re-executes itself, crun is entirely in C. This eliminates the overhead of Go runtime initialization and enables tighter integration with Linux syscalls for container setup (namespaces, cgroups, mounts).
libcrun: The shared library component that can be built with ./configure --enable-shared. It provides a C API for managing OCI containers programmatically, including Lua bindings.
Cgroup Management: crun supports both cgroupfs and systemd backends for resource control. On cgroup v2 systems, it automatically converts cgroup v1 OCI configurations using well-defined formulas for memory, CPU, blkio, and other controllers.
Global Options
--debug — produce verbose output--log=BACKEND:SPECIFIER — set log destination (file:PATH, journald:IDENTIFIER, ). Default is .
