GitHub Actions offers managed virtual environments for running workflows. In order for act to run your workflows locally, it must run a container for the runner defined in your workflow file. Here are the images that act uses for each runner type and size:

GitHub RunnerMicro Docker ImageMedium Docker ImageLarge Docker Image

If you want to run Windows and macOS based platforms and you are running act within that specfic environment you can opt out of docker and run them directly on your host system.

Here are some examples

act -P ubuntu-latest=-self-hosted
act -P windows-latest=-self-hosted
act -P macos-latest=-self-hosted

Default runners are intentionally incomplete

These default images do not contain all the tools that GitHub Actions offers by default in their runners. Many things can work improperly or not at all while running those image. Additionally, some software might still not work even if installed properly, since GitHub Actions are running in fully virtualized machines while act is using Docker containers (e.g. Docker does not support running systemd). In case of any problems please create issue in respective repository (issues with act in this repository, issues with nektos/act-environments-ubuntu:18.04 in nektos/act-environments and issues with any image from user catthehacker in catthehacker/docker_images)

Alternative runner images

If you need an environment that works just like the corresponding GitHub runner then consider using an image provided by nektos/act-environments:

:warning: :elephant: *** WARNING - this image is >18GB 😱***

Use an alternative runner image

To use a different image for the runner, use the -P option.

act -P <platform>=<docker-image>

If your workflow uses ubuntu-18.04, consider below line as an example for changing Docker image used to run that workflow:

act -P ubuntu-18.04=nektos/act-environments-ubuntu:18.04

If you use multiple platforms in your workflow, you have to specify them to change which image is used. For example, if your workflow uses ubuntu-18.04, ubuntu-16.04 and ubuntu-latest, specify all platforms like below

act -P ubuntu-18.04=nektos/act-environments-ubuntu:18.04 -P ubuntu-latest=ubuntu:latest -P ubuntu-16.04=node:16-buster-slim

Using local runner images

The --pull flag is set to true by default due to a breaking on older default docker images. This would pull the docker image everytime act is executed.

Set --pull to false if a local docker image is needed

  act --pull=false

Alternatively turn on offline mode

  act --action-offline-mode