What causes "failed to start container: %w" in nektos/act?

Check the wrapped Docker error (port conflicts, missing mounts, invalid entrypoint are common causes).

failed to start container: %w

Error message

failed to start container: %w

What it means

Error "failed to start container: %w" thrown in nektos/act.

Source

Thrown at pkg/container/docker_run.go:884

logger.Debugf("Starting container: %v", cr.id)

if _, err := cr.cli.ContainerStart(ctx, cr.id, client.ContainerStartOptions{}); err != nil {
	return fmt.Errorf("failed to start container: %w", err)
}

View on GitHub (pinned to 4f41128141)

Solutions

Check the wrapped Docker error (port conflicts, missing mounts, invalid entrypoint are common causes).
Verify ports used by the workflow are free on the host.
Ensure the image's entrypoint/cmd are valid for the container configuration.

When it happens

Trigger: Thrown at pkg/container/docker_run.go:884 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of nektos/act@4f41128141 (2026-08-15). Data as JSON: /api/errors/b7d5f1abe5f4aa0b. Report an issue: GitHub.