docs/engine/install/linux-postinstall.md

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Optional post-installation steps for Linux	Docker, Docker documentation, requirements, apt, installation, ubuntu, install, uninstall, upgrade, update	Post-installation steps for Linux	/engine/installation/linux/docker-ee/linux-postinstall/ /engine/installation/linux/linux-postinstall/ /install/linux/linux-postinstall/

These optional post-installation procedures shows you how to configure your Linux host machine to work better with Docker.

Manage Docker as a non-root user

The Docker daemon binds to a Unix socket, not a TCP port. By default it's the root user that owns the Unix socket, and other users can only access it using sudo. The Docker daemon always runs as the root user.

If you don't want to preface the docker command with sudo, create a Unix group called docker and add users to it. When the Docker daemon starts, it creates a Unix socket accessible by members of the docker group. On some Linux distributions, the system automatically creates this group when installing Docker Engine using a package manager. In that case, there is no need for you to manually create the group.

Warning

The docker group grants root-level privileges to the user. For details on how this impacts security in your system, see Docker Daemon Attack Surface. {: .warning}

Note

To run Docker without root privileges, see Run the Docker daemon as a non-root user (Rootless mode).

To create the docker group and add your user:

1. Create the docker group.

   $ sudo groupadd docker
   

2. Add your user to the docker group.

   $ sudo usermod -aG docker $USER
   

3. Log out and log back in so that your group membership is re-evaluated.

   If you're running Linux in a virtual machine, it may be necessary to restart the virtual machine for changes to take effect.

   You can also run the following command to activate the changes to groups:

   $ newgrp docker
   

4. Verify that you can run docker commands without sudo.

   $ docker run hello-world
   

   This command downloads a test image and runs it in a container. When the container runs, it prints a message and exits.

   If you initially ran Docker CLI commands using sudo before adding your user to the docker group, you may see the following error:

   WARNING: Error loading config file: /home/user/.docker/config.json -
   stat /home/user/.docker/config.json: permission denied
   

   This error indicates that the permission settings for the ~/.docker/ directory are incorrect, due to having used the sudo command earlier.

   To fix this problem, either remove the ~/.docker/ directory (it's recreated automatically, but any custom settings are lost), or change its ownership and permissions using the following commands:

   $ sudo chown "$USER":"$USER" /home/"$USER"/.docker -R
   $ sudo chmod g+rwx "$HOME/.docker" -R
   

Configure Docker to start on boot with systemd

Many modern Linux distributions use systemd to manage which services start when the system boots. On Debian and Ubuntu, the Docker service starts on boot by default. To automatically start Docker and containerd on boot for other Linux distributions using systemd, run the following commands:

$ sudo systemctl enable docker.service
$ sudo systemctl enable containerd.service

To stop this behavior, use disable instead.

$ sudo systemctl disable docker.service
$ sudo systemctl disable containerd.service

If you need to add an HTTP proxy, set a different directory or partition for the Docker runtime files, or make other customizations, see customize your systemd Docker daemon options.

Configure default logging driver

Docker provides logging drivers for collecting and viewing log data from all containers running on a host. The default logging driver, json-file, writes log data to JSON-formatted files on the host filesystem. Over time, these log files expand in size, leading to potential exhaustion of disk resources.

To avoid issues with overusing disk for log data, consider one of the following options:

• Configure the json-file logging driver to turn on log rotation
• Use an alternative logging driver such as the "local" logging driver that performs log rotation by default
• Use a logging driver that sends logs to a remote logging aggregator.

Configure where the Docker daemon listens for connections

By default, the Docker daemon listens for connections on a Unix socket to accept requests from local clients. It's possible to allow Docker to accept requests from remote hosts by configuring it to listen on an IP address and port as well as the Unix socket. For more detailed information on this configuration option, refer to the dockerd CLI reference.

Secure your connection

Before configuring Docker to accept connections from remote hosts it's critically important that you understand the security implications of opening Docker to the network. If steps aren't taken to secure the connection, it's possible for remote non-root users to gain root access on the host. For more information on how to use TLS certificates to secure this connection, check Protect the Docker daemon socket. {: .warning}

You can configure Docker to accept remote connections. This can be done using the docker.service systemd unit file for Linux distributions using systemd. Or you can use the daemon.json file, if your distribution doesn't use systemd.

systemd vs daemon.json

Configuring Docker to listen for connections using both the systemd unit file and the daemon.json file causes a conflict that prevents Docker from starting.

Configuring remote access with systemd unit file

1. Use the command sudo systemctl edit docker.service to open an override file for docker.service in a text editor.

2. Add or modify the following lines, substituting your own values.

   [Service]
   ExecStart=
   ExecStart=/usr/bin/dockerd -H fd:// -H tcp://127.0.0.1:2375
   

3. Save the file.

4. Reload the systemctl configuration.

    $ sudo systemctl daemon-reload
   

5. Restart Docker.

   $ sudo systemctl restart docker.service
   

6. Verify that the change has gone through.

   $ sudo netstat -lntp | grep dockerd
   tcp        0      0 127.0.0.1:2375          0.0.0.0:*               LISTEN      3758/dockerd
   

Configuring remote access with daemon.json

1. Set the hosts array in the /etc/docker/daemon.json to connect to the UNIX socket and an IP address, as follows:

   {
     "hosts": ["unix:///var/run/docker.sock", "tcp://127.0.0.1:2375"]
   }
   

2. Restart Docker.

3. Verify that the change has gone through.

   $ sudo netstat -lntp | grep dockerd
   tcp        0      0 127.0.0.1:2375          0.0.0.0:*               LISTEN      3758/dockerd
   

Enable IPv6 on the Docker daemon

To enable IPv6 on the Docker daemon, see Enable IPv6 support.

Next steps

• Take a look at the Get started training modules to learn how to build an image and run it as a containerized application.
• Review the topics in Develop with Docker to learn how to build new applications using Docker.