Mini Docker

A learning project exploring core Linux container primitives in Go.

Current State

The current implementation uses a re-exec flow to start an isolated /bin/sh process:

• The parent process (runtime.Run()) checks for an existing root filesystem and re-executes the current binary (/proc/self/exe) with new PID, UTS, and mount namespaces.
• The re-executed child process (runtime.ContainerInit()) isolates the mount namespace, configures an overlay filesystem, pivots the root (pivot_root), mounts /proc, and starts /bin/sh.

The process is attached to the caller's terminal through standard input, output, and error streams.

Structure

• main.go: program entry point; branches between parent and child execution based on the CONTAINER_INIT environment variable.
• runtime/run.go: handles both parent (namespace setup) and child (filesystem isolation, shell execution) lifecycles.
• runtime/rootfs.go: handles the pivot_root functionality for the new filesystem root.
• runtime/utils.go: utility functions for checking and creating directories.
• cli/run.go: package stub reserved for future CLI work

Planned Direction

The broader project is intended to grow toward:

• more namespace isolation (e.g., network, user)
• cgroup-based resource limits
• dynamic image handling, unpacking, and cleanup
• command parsing and additional runtime lifecycle features

Note: This is an educational tool, not for production.