runc
also: OCI runtime
runc is a lightweight container runtime that creates and runs containers according to the OCI (Open Container Initiative) specification. It is the low-level tool that actually executes containerized applications on Linux.
runc is a command-line tool developed by Docker and the Linux Foundation that serves as the reference implementation of the OCI container runtime specification. It handles the low-level mechanics of creating isolated Linux environments (containers) using kernel features like namespaces and cgroups.
While higher-level container platforms like Docker and Kubernetes manage images, networking, and orchestration, runc does the actual work of spawning and managing container processes. For example, Docker internally uses runc to start containers: runc run my-container launches a container from an OCI bundle (a directory containing a configuration file and rootfs).
runc is particularly useful for building container infrastructure, integrating containers into custom systems, and understanding how containerization works at the kernel level. Its minimalist design makes it ideal for embedded systems and specialized container implementations.