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Understand permission requirements for Docker Desktop on Mac

This page contains information about the permission requirements for running and installing Docker Desktop on Mac.

It also provides clarity on running containers as root as opposed to having root access on the host.

Permission requirements link

Docker Desktop for Mac is run as an unprivileged user. However, certain functionalities are required for Docker Desktop to perform a limited set of privileged configurations such as:

Installing symlinks in /usr/local/bin .
Binding privileged ports that are less than 1024. The so-called "privileged ports" are not generally used as a security boundary, however operating systems still prevent unprivileged processes from binding them which breaks commands like docker run -p 127.0.0.1:80:80 docker/getting-started .
Ensuring localhost and kubernetes.docker.internal are defined in /etc/hosts . Some old macOS installs don't have localhost in /etc/hosts , which causes Docker to fail. Defining the DNS name kubernetes.docker.internal allows Docker to share Kubernetes contexts with containers.
Securely caching the Registry Access Management policy which is read-only for the developer.

Depending on which version of Docker Desktop for Mac is used, privileged access is granted either during installation, first run, or only when it's needed.

Version 4.15 - 4.17 Versions prior to 4.15

From version 4.18 and later, Docker Desktop for Mac provides greater control over functionality that's enabled during installation.

The first time Docker Desktop for Mac launches, you are presented with an installation window where you can choose to either use the default settings, which work for most developers and require privileged access to be granted, or use advanced settings.

If you work in an environment with elevated security requirements, for instance where local administrative access is prohibited, then you can use the advanced settings to remove the need for granting privileged access. You can configure:

The location of the Docker CLI tools either in the system or user directory
The default Docker socket
Privileged port mapping

Depending on which advanced settings you configure, you must enter your password to confirm.

You can change these configurations at a later date from the Advanced page in Settings .

Versions 4.15 to 4.17 of Docker Desktop for Mac don't require the privileged process to run permanently. Whenever elevated privileges are needed for a configuration, Docker Desktop prompts you with information on the task it needs to perform. Most configurations are applied once, subsequent runs don't prompt for privileged access anymore. The only time Docker Desktop may start the privileged process is for binding privileged ports that aren't allowed by default on the host OS.

Versions prior to 4.15 of Docker Desktop for Mac require root access to be granted on the first run. The first time that Docker Desktop is launched you receive an admin prompt to grant permission for the installation of the com.docker.vmnetd privileged helper service. For subsequent runs, root privileges aren't required. Following the principle of least privilege, this approach allows root access to be used only for the operations for which it's absolutely necessary, while still being able to use Docker Desktop as an unprivileged user. All privileged operations are run using the privileged helper process com.docker.vmnetd .

Installing symlinks link

The Docker binaries are installed by default in /Applications/Docker.app/Contents/Resources/bin . Docker Desktop ensures the Docker CLI is on your PATH without having to reconfigure shells, log out then log back in for example. As on most systems /usr/local/bin is on the PATH by default, and so Docker Desktop creates symlinks for all Docker binaries in it.

Version 4.17 and earlier

With version 4.18 and later, you can choose whether to install symlinks either in /usr/local/bin or $HOME/.docker/bin during installation of Docker Desktop.

If /usr/local/bin is chosen, and this location is not writable by unprivileged users, Docker Desktop requires authorization to confirm this choice before the symlinks to Docker binaries are created in /usr/local/bin . If $HOME/.docker/bin is chosen, authorization is not required, but the you must manually add $HOME/.docker/bin to their PATH.

You are also given the option to enable the installation of the /var/run/docker.sock symlink. Creating this symlink ensures various Docker clients relying on the default Docker socket path to work without additional changes.

As the /var/run is mounted as a tmpfs, its content is deleted on restart, symlink to the Docker socket included. To ensure the Docker socket exists after restart, Docker Desktop sets up a launchd startup task that creates the symlink by running ln -s -f /Users/<user>/.docker/run/docker.sock /var/run/docker.sock . This ensures the you aren't prompted on each startup to create the symlink. If you don't enable this option at installation, the symlink and the startup task is not created and you may have to explicitly set the DOCKER_HOST environment variable to /Users/<user>/.docker/run/docker.sock in the clients it is using. The Docker CLI relies on the current context to retrieve the socket path, the current context is set to desktop-linux on Docker Desktop startup.

For versions prior to 4.18, installing symlinks in /usr/local/bin is a privileged configuration Docker Desktop performs on the first startup. Docker Desktop checks if symlinks exists and takes the following actions:

Creates the symlinks without the admin prompt if /usr/local/bin is writable by unprivileged users.
Triggers an admin prompt for you to authorize the creation of symlinks in /usr/local/bin . If you authorizes this, symlinks to Docker binaries are created in /usr/local/bin . If you reject the prompt, are not willing to run configurations requiring elevated privileges, or don't have admin rights on your machine, Docker Desktop creates the symlinks in ~/.docker/bin and edits your shell profile to ensure this location is in your PATH. This requires all open shells to be reloaded. The rejection is recorded for future runs to avoid prompting you again. For any failure to ensure binaries are on your PATH, you may need to manually add to their PATH the /Applications/Docker.app/Contents/Resources/bin or use the full path to Docker binaries.

A particular case is the installation of the /var/run/docker.sock symlink. Creating this symlink ensures various Docker clients relying on the default Docker socket path to work without additional changes. As the /var/run is mounted as a tmpfs, its content is deleted on restart, symlink to Docker socket included. To ensure the Docker socket exists after restart, Docker Desktop sets up a launchd startup task that creates the symlink by running ln -s -f /Users/<user>/.docker/run/docker.sock /var/run/docker.sock . This ensures that you are not prompted on each startup to create the symlink. If you reject the prompt, the symlink and the startup task is not created and you may have to explicitly set the DOCKER_HOST to /Users/<user>/.docker/run/docker.sock in the clients it is using. The Docker CLI relies on the current context to retrieve the socket path, the current context is set to desktop-linux on Docker Desktop startup.

Binding privileged ports Version 4.18 and later Version 4.17 and earlier

With version 4.18 and later you can choose to enable privileged port mapping during installation, or from the Advanced page in Settings post-installation. Docker Desktop requires authorization to confirm this choice.

For versions below 4.18 , if you run a container that requires binding privileged ports, Docker Desktop first attempts to bind it directly as an unprivileged process. If the OS prevents this and it fails, Docker Desktop checks if the com.docker.vmnetd privileged helper process is running to bind the privileged port through it.

If the privileged helper process is not running, Docker Desktop prompts you for authorization to run it under launchd open_in_new . This configures the privileged helper to run as in the versions of Docker Desktop prior to 4.15. However, the functionality provided by this privileged helper now only supports port binding and caching the Registry Access Management policy. If you decline the launch of the privileged helper process, binding the privileged port cannot be done and the Docker CLI returns an error:

$ docker run -p 127.0.0.1:80:80 docker/getting-started
docker: Error response from daemon: Ports are not available: exposing port
TCP 127.0.0.1:80 -> 0.0.0.0:0: failed to connect to /var/run/com.docker.vmnetd.sock:
is vmnetd running?: dial unix /var/run/com.docker.vmnetd.sock: connect: connection
refused.
ERRO[0003] error waiting for container: context canceled

Note

The command may fail with the same error if you take too long to authorize the prompt to start the helper process, as it may timeout.

Ensuring localhost and kubernetes.docker.internal are defined Version 4.18 and later Version 4.17 and earlier

With versions 4.18 and later, it is your responsibility to ensure that localhost is resolved to `127.0.0.1` and if Kubernetes is used, that `kubernetes.docker.internal` is resolved to `127.0.0.1` .

On first run, Docker Desktop checks if `localhost` is resolved to `127.0.0.1` . In case the resolution fails, it prompts you to allow adding the mapping to `/etc/hosts` . Similarly, when the Kubernetes cluster is installed, it checks that `kubernetes.docker.internal` is resolved to `127.0.0.1` and prompts you to do so.

Installing from the command line link

In version 4.11 and later of Docker Desktop for Mac, privileged configurations are applied during the installation with the --user flag on the install command . In this case, you are not prompted to grant root privileges on the first run of Docker Desktop. Specifically, the --user flag:

Uninstalls the previous com.docker.vmnetd if present
Sets up symlinks
Ensures that localhost is resolved to 127.0.0.1

The limitation of this approach is that Docker Desktop can only be run by one user-account per machine, namely the one specified in the -–user flag.

Privileged helper link

In the limited situations when the privileged helper is needed, for example binding privileged ports or caching the Registry Access Management policy, the privileged helper is started by launchd and runs in the background unless it is disabled at runtime as previously described. The Docker Desktop backend communicates with the privileged helper over the UNIX domain socket /var/run/com.docker.vmnetd.sock . The functionalities it performs are:

Binding privileged ports that are less than 1024.
Securely caching the Registry Access Management policy which is read-only for the developer.
Uninstalling the privileged helper.

The removal of the privileged helper process is done in the same way as removing launchd processes.

$ ps aux | grep vmnetd                                                
root             28739   0.0  0.0 34859128    228   ??  Ss    6:03PM   0:00.06 /Library/PrivilegedHelperTools/com.docker.vmnetd
user             32222   0.0  0.0 34122828    808 s000  R+   12:55PM   0:00.00 grep vmnetd
$ sudo launchctl unload -w /Library/LaunchDaemons/com.docker.vmnetd.plist
Password:
$ ps aux | grep vmnetd                                                   
user             32242   0.0  0.0 34122828    716 s000  R+   12:55PM   0:00.00 grep vmnetd
$ rm /Library/LaunchDaemons/com.docker.vmnetd.plist 
$ rm /Library/PrivilegedHelperTools/com.docker.vmnetd