Agent-Skills.md

Agent Skills: Apple Container Skill

Interact with the Apple Container CLI to manage containers, images, volumes, networks, and system services on macOS. Use this skill when the user asks to run, build, or inspect containers or manage the container runtime.

UncategorizedID: gabeosx/agent-skills/apple-container-skill

Repository

gabeosx/agent-skills
gabeosx
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pnpm dlx add-skill https://github.com/gabeosx/agent-skills/tree/HEAD/skills/apple-container-skill

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skills/apple-container-skill/SKILL.md

Skill Metadata

Name
apple-container-skill
Description
Use Apple's `container` CLI on Apple silicon macOS for Linux containers, OCI image builds, registries, volumes, networks, port forwarding, host access, and persistent `container machine` Linux environments. Use this skill whenever the user asks to replace Docker Desktop with Apple Container, run Linux commands on macOS, build/run/inspect Apple containers, debug Apple Container service/network/build failures, or use Container Machines.

Apple Container Skill

Operate Apple's container CLI as a native macOS Linux container runtime. This skill should guide the agent's choices, not just provide command syntax.

First Moves

Before doing real work, establish whether the host and runtime are usable:

sw_vers
uname -m
command -v container
container --version
container system status
  • Require Apple silicon (arm64). Current Apple docs support macOS 26+ for real use; macOS 15 has important networking limitations.
  • If the CLI is missing, prefer Apple's signed installer from the GitHub releases page. Homebrew can work, but if container system start fails with missing plugins after a Homebrew install, upgrade/reinstall the formula.
  • Start services with container system start when status shows they are stopped. First start may prompt to install the recommended Linux kernel.
  • Run a smoke test before blaming application code:
container run --rm docker.io/library/alpine:latest sh -lc 'uname -a; nslookup github.com'

For an unknown or flaky environment, run the bundled diagnostic:

bash skills/apple-container-skill/scripts/diagnose.sh

Choose The Right Runtime Shape

  • Use container run for disposable app containers, one-shot Linux commands, project dev shells, image smoke tests, and services whose state should live in bind mounts or named volumes.
  • Use container machine for a long-lived Linux workspace: repeated distro testing, system services, VS Code Remote SSH, a persistent root filesystem, or "edit on macOS, build inside Linux" loops.
  • Do not describe machines as merely "persistent containers." A machine is a convenience wrapper around a container, a separate persistent root disk, and host integration. It maps the host user, forwards SSH agent support, and mounts the macOS home at /Users/<user> while the Linux user's $HOME is /home/<user>.
  • Plain OCI application images may fail in machine mode because machines need a bootable init system. Plain alpine:3.22 can create, inspect, and stop but fail command execution if /sbin/openrc is absent. Build an OpenRC-capable Alpine image or a systemd-capable Ubuntu/Debian image for reliable container machine run.
  • For scripted machine commands, prefer an option terminator: container machine run -n dev -- whoami or container machine run -n dev -- /bin/sh -c 'whoami; pwd; echo "$HOME"'. Avoid -i in heredoc/non-interactive scripts because it can consume the rest of the script from stdin.

Machine Image Selection

When the user names a distro image, preserve the distro choice but choose the runtime shape correctly:

  • For one-shot commands or app containers, use the requested image directly with container run.
  • For container machine, treat the requested image as a base image unless it is already known to be machine-capable.
  • Do not silently try to use plain ubuntu, debian, or alpine app images as long-lived machines. Explain that machines boot an init system, then derive a machine image from the requested base.
  • For Alpine machines, add OpenRC and related user/network tools, set CMD ["/sbin/init"], then build a local *-machine image.
  • For Ubuntu/Debian machines, add systemd, dbus, sudo, SSH/network tools as needed, set the systemd target, and build a local *-machine image.
  • If the user insists on the exact image without derivation, use container run or warn that container machine may create but fail to boot or execute commands.

Safety Rules

Ask before:

  • Running sudo, installing, upgrading, uninstalling, or changing DNS resolver entries.
  • Global cleanup: container prune, container image prune, container volume prune, container network prune, or deleting all resources.
  • Deleting named machines, volumes, images, or containers that were not created for the current task.
  • Editing ~/.ssh/config, changing host firewall/VPN settings, or widening bind mounts beyond the project directory.

Prefer graceful stops (container stop, container machine stop) before forceful deletion or container kill.

Practical Defaults

Common project shell:

container run --rm -it -v "$PWD:/work" -w /work docker.io/library/ubuntu:24.04 bash

Build and run an image:

container build -t local/app:dev .
container run --rm -p 8080:8080 local/app:dev

Long-lived machine:

container machine create local/alpine-machine:latest --name dev --set-default --cpus 4 --memory 8G
container machine run -n dev -- /bin/sh -c 'whoami; pwd; echo "$HOME"'
container machine stop dev

Important Current Behaviors

  • container system property get, set, and clear were removed in 1.0. Use ~/.config/container/config.toml for defaults and container system property list only to inspect effective config.
  • Apple's signed installer places the CLI at /usr/local/bin/container; check that path directly when a fresh shell cannot find container.
  • container build may leave the BuildKit builder running. If a validation task must leave no runtime processes, inspect container builder status, then use container builder stop and container builder delete.
  • Host-to-container traffic should usually use -p/--publish; if it fails, check that the app listens on 0.0.0.0 inside the container.
  • Treat named volumes as single-attachment unless the workflow has proven otherwise; do not assume the same named volume can be attached concurrently to multiple running containers.
  • Container-to-host traffic does not use Docker's magic host alias. Configure a localhost DNS domain:
sudo container system dns create host.container.internal --localhost 203.0.113.113

This can disable Private Relay, and packet-filter rules may need recreation after reboot.

  • container network user-defined networks require macOS 26+. On macOS 15, container-to-container networking and multiple networks are limited.
  • If networking worked and then fails after VPN or endpoint security changes, suspect vmnet/VPN routing before changing application code.

References