Frequently asked questions (FAQ)

Looking for popular FAQs on Docker for Mac? Check out the Docker Knowledge Hub for knowledge base articles, FAQs, technical support for various subscription levels, and more.

Stable and beta channels

Q: How do I get the stable or beta version of Docker for Mac?

A: Use the download links for the channels given in the topic Download Docker for Mac.

This topic also has more information about the two channels.

Q: What is the difference between the stable and beta versions of Docker for Mac?

A: Two different download channels are available for Docker for Mac:

• The stable channel provides a general availability release-ready installer for a fully baked and tested, more reliable app. The stable version of Docker for Mac comes with the latest released version of Docker Engine. The release schedule is synched with Docker Engine releases and hotfixes. On the stable channel, you can select whether to send usage statistics and other data.

• The beta channel provides an installer with new features we are working on, but is not necessarily fully tested. It comes with the experimental version of Docker Engine. Bugs, crashes and issues are more likely to occur with the beta app, but you get a chance to preview new functionality, experiment, and provide feedback as the apps evolve. Releases are typically more frequent than for stable, often one or more per month. Usage statistics and crash reports are sent by default. You do not have the option to disable this on the beta channel.

Q: Can I switch back and forth between stable and beta versions of Docker for Mac?

A: Yes, you can switch between versions to try out the betas to see what’s new, then go back to stable for other work. However, you can have only one app installed at a time. Switching back and forth between stable and beta apps can destabilize your development environment, particularly in cases where you switch from a newer (beta) channel to older (stable).

For example, containers created with a newer beta version of Docker for Mac may not work after you switch back to stable because they may have been created leveraging beta features that aren’t in stable yet. Just keep this in mind as you create and work with beta containers, perhaps in the spirit of a playground space where you are prepared to troubleshoot or start over.

Do the following each time:

1. Use docker save to save any images you want to keep. (See save in the Docker Engine command line reference.)

2. Use docker export to export containers you want to keep. (See export in the Docker Engine command line reference.)

3. Uninstall the current app (whether stable or beta).

4. Install a different version of the app (stable or beta).

What is Docker.app?

Docker.app is Docker for Mac, a bundle of Docker client, and Docker Engine. Docker.app uses the macOS Hypervisor.framework (part of macOS 10.10 Yosemite and higher) to run containers, meaning that no separate VirtualBox is required.

What kind of feedback are we looking for?

Everything is fair game. We’d like your impressions on the download-install process, startup, functionality available, the GUI, usefulness of the app, command line integration, and so on. Tell us about problems, what you like, or functionality you’d like to see added.

We are especially interested in getting feedback on the new swarm mode described in Docker Swarm. A good place to start is the tutorial.

What if I have problems or questions?

You can find the list of frequent issues in Logs and Troubleshooting.

If you do not find a solution in Troubleshooting, browse issues on Docker for Mac issues on GitHub or create a new one. You can also create new issues based on diagnostics. To learn more, see Diagnose problems, send feedback, and create GitHub issues.

Docker for Mac forum provides discussion threads as well, and you can create discussion topics there, but we recommend using the GitHub issues over the forums for better tracking and response.

Can I use Docker for Mac with new swarm mode?

Yes, you can use Docker for Mac to test single-node features of swarm mode introduced with Docker Engine 1.12, including initializing a swarm with a single node, creating services, and scaling services. Docker “Moby” on Hyperkit will serve as the single swarm node. You can also use Docker Machine, which comes with Docker for Mac, to create and experiment a multi-node swarm. Check out the tutorial at Get started with swarm mode.

How do I connect to the remote Docker Engine API?

You might need to provide the location of the Engine API for Docker clients and development tools.

On Docker for Mac, clients can connect to the Docker Engine through a Unix socket: unix:///var/run/docker.sock.

See also Docker Engine API and Docker for Mac forums topic Using pycharm Docker plugin...

If you are working with applications like Apache Maven that expect settings for DOCKER_HOST and DOCKER_CERT_PATH environment variables, specify these to connect to Docker instances through Unix sockets. For example:

export DOCKER_HOST=unix:///var/run/docker.sock

How do I connect from a container to a service on the host?

The Mac has a changing IP address (or none if you have no network access). Our current recommendation is to attach an unused IP to the lo0 interface on the Mac so that containers can connect to this address.

For a full explanation and examples, see I want to connect from a container to a service on the host under Known Limitations, Use Cases, and Workarounds in the Networking topic.

How do I to connect to a container from the Mac?

Our current recommendation is to publish a port, or to connect from another container. Note that this is what you have to do even on Linux if the container is on an overlay network, not a bridge network, as these are not routed.

For a full explanation and examples, see I want to connect to a container from the Mac under Known Limitations, Use Cases, and Workarounds in the Networking topic.

How do I add custom CA certificates?

Starting with Docker for Mac Beta 27 and Stable 1.12.3, all trusted certificate authorities (CAs) (root or intermediate) are supported.

Docker for Mac creates a certificate bundle of all user-trusted CAs based on the Mac Keychain, and appends it to Moby trusted certificates. So if an enterprise SSL certificate is trusted by the user on the host, it will be trusted by Docker for Mac.

To manually add a custom, self-signed certificate, start by adding the certificate to the Mac’s keychain, which will be picked up by Docker for Mac. Here is an example.

sudo security add-trusted-cert -d -r trustRoot -k /Library/Keychains/System.keychain ca.crt

For a complete explanation of how to do this, see the blog post Adding Self-signed Registry Certs to Docker & Docker for Mac.

How do I reduce the size of Docker.qcow2?

By default Docker for Mac stores containers and images in a file ~/Library/Containers/com.docker.docker/Data/com.docker.driver.amd64-linux/Docker.qcow2. This file grows on-demand up to a default maximum file size of 64GiB.

In Docker 1.12 the only way to free space on the host is to delete this file and restart the app. Unfortunately this removes all images and containers.

In Docker 1.13 there is preliminary support for “TRIM” to non-destructively free space on the host. First free space within the Docker.qcow2 by removing unneeded containers and images with the following commands:

• docker ps -a: list all containers
• docker image ls: list all images
• docker system prune: (new in 1.13): deletes all stopped containers, all volumes not used by at least one container and all images without at least one referring container.

Note the Docker.qcow2 will not shrink in size immediately. In 1.13 a background cron job runs fstrim every 15 minutes. If the space needs to be reclaimed sooner, run this command:

docker run --rm -it --privileged --pid=host walkerlee/nsenter -t 1 -m -u -i -n fstrim /var

Once the fstrim has completed, restart the app. When the app shuts down, it will compact the file and free up space. The app will take longer than usual to restart because it must wait for the compaction to complete.

For background conversation thread on this, see Docker.qcow2 never shrinks .. on Docker for Mac GitHub issues.

What are system requirements for Docker for Mac?

Note that you need a Mac that supports hardware virtualization and can run at least macOS 10.10.3+ or 10.11 (macOS Yosemite or macOS El Capitan). See also “What to know before you install” in Getting Started.

Do I need to uninstall Docker Toolbox to use Docker for Mac?

No, you can use these side by side. Docker Toolbox leverages a Docker daemon installed using docker-machine in a machine called default. Running eval $(docker-machine env default) in a shell sets DOCKER environment variables locally to connect to the default machine using Engine from Toolbox. To check whether Toolbox DOCKER environment variables are set, run env | grep DOCKER.

To make the client talk to the Docker for Mac Engine, run the command unset ${!DOCKER_*} to unset all DOCKER environment variables in the current shell. (Now, env | grep DOCKER should return no output.) You can have multiple command line shells open, some set to talk to Engine from Toolbox and others set to talk to Docker for Mac. The same applies to docker-compose.

How do I uninstall Docker Toolbox?

You might decide that you do not need Toolbox now that you have Docker for Mac, and want to uninstall it. For details on how to perform a clean uninstall of Toolbox on the Mac, see How to uninstall Toolbox in the Toolbox Mac topics.

What is HyperKit?

HyperKit is a hypervisor built on top of the Hypervisor.framework in macOS 10.10 Yosemite and higher. It runs entirely in userspace and has no other dependencies.

We use HyperKit to eliminate the need for other VM products, such as Oracle Virtualbox or VMWare Fusion.

What is the benefit of HyperKit?

It is thinner than VirtualBox and VMWare fusion, and the version we include is tailor made for Docker workloads on the Mac.

Why is com.docker.vmnetd running after I quit the app?

The privileged helper process com.docker.vmnetd is started by launchd and runs in the background. The process will not consume any resources unless Docker.app connects to it, so it’s safe to ignore.

Can I pass through a USB device to a container?

Unfortunately it is not possible to pass through a USB device (or a serial port) to a container. For use cases requiring this, we recommend the use of Docker Toolbox.

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