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Getting Started ​

Based on container2wasm v0.8.x. Commands assume a Linux or macOS host with Docker Buildx and a WASI runtime available.

Prerequisites ​

  • Docker with Buildx (the conversion runs through BuildKit).
  • A WASI runtime to execute the output, for example wasmtime.
  • To build c2w from source, a Go toolchain and make. Prebuilt binaries are also published on the releases page.

Install ​

bash
make
sudo make install

make builds the c2w and c2w-net binaries (Makefile:16, Makefile:19); sudo make install places them on your PATH. Alternatively, download a release binary from the project's releases page.

A first working setup ​

  1. Convert a container image to a .wasm file. This drives Docker Buildx and can take a while on the first run.

    bash
    c2w ubuntu:22.04 out.wasm

  2. Run the output on a WASI runtime. The .wasm boots an emulated Linux and runs the command in the container.

    bash
    wasmtime out.wasm uname -a

  3. Map a host directory into the guest. The WASI filesystem exposes it and the emulator mounts it over 9p.

    bash
    wasmtime --mapdir /mnt/share::/tmp/share out.wasm cat /mnt/share/from-host

To target riscv64 instead of the default amd64, pass --target-arch:

bash
c2w --target-arch=riscv64 riscv64/ubuntu:22.04 out.wasm

For a browser build, use --to-js to emit JavaScript and Wasm assets:

bash
c2w --to-js alpine:3.20 /tmp/out-js/htdocs/

Verify it works ​

If wasmtime out.wasm uname -a prints a Linux kernel string, the emulator booted, runc started the container, and the command ran inside it. Because the default optimization mode uses a wizer pre-boot snapshot (Dockerfile:29), startup skips the kernel boot and resumes from the snapshot, so the first line of output should appear quickly. Networking needs the host-side c2w-net helper, since WASI has no sockets.

Where to go next ​

  • The README documents supported runtimes, browser output, and networking with c2w-net.
  • Note the license caveat before redistributing: the generated .wasm bundles emulator code under LGPL-2.1 and other licenses.
  • The project is experimental and CNCF Sandbox stage; treat performance and stability accordingly.

Sources ​

  1. container2wasm README, accessed 2026-06-26.
  2. container2wasm source at commit 74662a2, accessed 2026-06-26.