Docker linux post install

Linux post-installation steps for Docker Engine

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.

To create the docker group and add your user:

$ sudo usermod -aG docker $USER 

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

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.

Next steps

• Read 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.

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Post-installation steps for Linux

This section contains optional procedures for configuring Linux hosts to work better with Docker.

Manage Docker as a non-root user

The Docker daemon binds to a Unix socket instead of a TCP port. By default that Unix socket is owned by the user root 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.

Warning

The docker group grants privileges equivalent to the root user. For details on how this impacts security in your system, see Docker Daemon Attack Surface.

To create the docker group and add your user:

$ sudo usermod -aG docker $USER 

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, which indicates that your ~/.docker/ directory was created with incorrect permissions due to the sudo commands.

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

To fix this problem, either remove the ~/.docker/ directory (it is 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

Most current Linux distributions (RHEL, CentOS, Fedora, Debian, Ubuntu 16.04 and higher) use systemd to manage which services start when the system boots. On Debian and Ubuntu, the Docker service is configured to start on boot by default. To automatically start Docker and Containerd on boot for other distros, use the commands below:

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

To disable 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.

Use a different storage engine

For information about the different storage engines, see Storage drivers. The default storage engine and the list of supported storage engines depend on your host’s Linux distribution and available kernel drivers.

Configure default logging driver

Docker provides the capability to collect and view log data from all containers running on a host via a series of logging drivers. 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 alleviate such issues, either configure the json-file logging driver to enable log rotation, use an alternative logging driver such as the “local” logging driver that performs log rotation by default, or 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 is 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 take a look at “Bind Docker to another host/port or a unix socket” section of the Docker CLI Reference article.

Secure your connection

Before configuring Docker to accept connections from remote hosts it is critically important that you understand the security implications of opening docker to the network. If steps are not taken to secure the connection, it is 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 this article on how to protect the Docker daemon socket.

Configuring Docker to accept remote connections can be done with the docker.service systemd unit file for Linux distributions using systemd, such as recent versions of RedHat, CentOS, Ubuntu and SLES, or with the daemon.json file which is recommended for Linux distributions that do not 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 

 $ sudo systemctl daemon-reload 

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