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Ubuntu

Docker is supported on these Ubuntu operating systems:

  • Ubuntu Vivid 15.04
  • Ubuntu Trusty 14.04 (LTS)
  • Ubuntu Precise 12.04 (LTS)
  • Ubuntu Saucy 13.10

This page instructs you to install using Docker-managed release packages and installation mechanisms. Using these packages ensures you get the latest release of Docker. If you wish to install using Ubuntu-managed packages, consult your Ubuntu documentation.

Prerequisites

Docker requires a 64-bit installation regardless of your Ubuntu version. Additionally, your kernel must be 3.10 at minimum. The latest 3.10 minor version or a newer maintained version are also acceptable.

Kernels older than 3.10 lack some of the features required to run Docker containers. These older versions are known to have bugs which cause data loss and frequently panic under certain conditions.

To check your current kernel version, open a terminal and use uname -r to display your kernel version:

$ uname -r 
3.11.0-15-generic

Caution Some Ubuntu OS versions require a version higher than 3.10 to run Docker, see the prerequisites on this page that apply to your Ubuntu version.

For Vivid 15.04

There are no prerequisites for this version.

For Trusty 14.04

There are no prerequisites for this version.

For Precise 12.04 (LTS)

For Ubuntu Precise, Docker requires the 3.13 kernel version. If your kernel version is older than 3.13, you must upgrade it. Refer to this table to see which packages are required for your environment:

linux-image-generic-lts-trusty Generic Linux kernel image. This kernel has AUFS built in. This is required to run Docker.
linux-headers-generic-lts-trusty Allows packages such as ZFS and VirtualBox guest additions which depend on them. If you didn’t install the headers for your existing kernel, then you can skip these headers for the”trusty” kernel. If you’re unsure, you should include this package for safety.
xserver-xorg-lts-trusty Optional in non-graphical environments without Unity/Xorg. Required when running Docker on machine with a graphical environment.

To learn more about the reasons for these packages, read the installation instructions for backported kernels, specifically the LTS Enablement Stack — refer to note 5 under each version.

libgl1-mesa-glx-lts-trusty
 

To upgrade your kernel and install the additional packages, do the following:

  1. Open a terminal on your Ubuntu host.

  2. Update your package manager.

    $ sudo apt-get update
    
  3. Install both the required and optional packages.

    $ sudo apt-get install linux-image-generic-lts-trusty
    

    Depending on your environment, you may install more as described in the preceding table.

  4. Reboot your host.

    $ sudo reboot
    
  5. After your system reboots, go ahead and install Docker.

For Saucy 13.10 (64 bit)

Docker uses AUFS as the default storage backend. If you don’t have this prerequisite installed, Docker’s installation process adds it.

Installation

Make sure you have installed the prerequisites for your Ubuntu version. Then, install Docker using the following:

  1. Log into your Ubuntu installation as a user with sudo privileges.

  2. Verify that you have curl installed.

    $ which curl
    

    If curl isn’t installed, install it after updating your manager:

    $ sudo apt-get update
    $ sudo apt-get install curl
    
  3. Get the latest Docker package.

    $ curl -sSL https://get.docker.com/ | sh
    

    The system prompts you for your sudo password. Then, it downloads and installs Docker and its dependencies.

Note: If your company is behind a filtering proxy, you may find that the apt-key command fails for the Docker repo during installation. To work around this, add the key directly using the following:

  $ curl -sSL https://get.docker.com/gpg | sudo apt-key add -
  1. Verify docker is installed correctly.

    $ sudo docker run hello-world
    

    This command downloads a test image and runs it in a container.

Optional configurations for Docker on Ubuntu

This section contains optional procedures for configuring your Ubuntu to work better with Docker.

Create a Docker group

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 access it with sudo. For this reason, docker daemon always runs as the root user.

To avoid having to use sudo when you use the docker command, create a Unix group called docker and add users to it. When the docker daemon starts, it makes the ownership of the Unix socket read/writable by the docker group.

Warning: The docker group is equivalent to the root user; For details on how this impacts security in your system, see Docker Daemon Attack Surface for details.

To create the docker group and add your user:

  1. Log into Ubuntu as a user with sudo privileges.

    This procedure assumes you log in as the ubuntu user.

  2. Create the docker group and add your user.

    $ sudo usermod -aG docker ubuntu
    
  3. Log out and log back in.

    This ensures your user is running with the correct permissions.

  4. Verify your work by running docker without sudo.

    $ docker run hello-world
    

    If this fails with a message similar to this:

    Cannot connect to the Docker daemon. Is 'docker daemon' running on this host?
    

    Check that the DOCKER_HOST environment variable is not set for your shell. If it is, unset it.

Adjust memory and swap accounting

When users run Docker, they may see these messages when working with an image:

WARNING: Your kernel does not support cgroup swap limit. WARNING: Your
kernel does not support swap limit capabilities. Limitation discarded.

To prevent these messages, enable memory and swap accounting on your system. Enabling memory and swap accounting does induce both a memory overhead and a performance degradation even when Docker is not in use. The memory overhead is about 1% of the total available memory. The performance degradation is roughly 10%.

To enable memory and swap on system using GNU GRUB (GNU GRand Unified Bootloader), do the following:

  1. Log into Ubuntu as a user with sudo privileges.

  2. Edit the /etc/default/grub file.

  3. Set the GRUB_CMDLINE_LINUX value as follows:

    GRUB_CMDLINE_LINUX="cgroup_enable=memory swapaccount=1"
    
  4. Save and close the file.

  5. Update GRUB.

    $ sudo update-grub
    
  6. Reboot your system.

Enable UFW forwarding

If you use UFW (Uncomplicated Firewall) on the same host as you run Docker, you’ll need to do additional configuration. Docker uses a bridge to manage container networking. By default, UFW drops all forwarding traffic. As a result, for Docker to run when UFW is enabled, you must set UFW’s forwarding policy appropriately.

Also, UFW’s default set of rules denies all incoming traffic. If you want to be able to reach your containers from another host then you should also allow incoming connections on the Docker port (default 2375).

To configure UFW and allow incoming connections on the Docker port:

  1. Log into Ubuntu as a user with sudo privileges.

  2. Verify that UFW is installed and enabled.

    $ sudo ufw status
    
  3. Open the /etc/default/ufw file for editing.

    $ sudo nano /etc/default/ufw
    
  4. Set the DEFAULT_FORWARD_POLICY policy to:

    DEFAULT_FORWARD_POLICY="ACCEPT"
    
  5. Save and close the file.

  6. Reload UFW to use the new setting.

    $ sudo ufw reload
    
  7. Allow incoming connections on the Docker port.

    $ sudo ufw allow 2375/tcp
    

Configure a DNS server for use by Docker

Systems that run Ubuntu or an Ubuntu derivative on the desktop typically use 127.0.0.1 as the default nameserver in /etc/resolv.conf file. The NetworkManager also sets up dnsmasq to use the real DNS servers of the connection and sets up nameserver 127.0.0.1 in /etc/resolv.conf.

When starting containers on desktop machines with these configurations, Docker users see this warning:

WARNING: Local (127.0.0.1) DNS resolver found in resolv.conf and containers
can't use it. Using default external servers : [8.8.8.8 8.8.4.4]

The warning occurs because Docker containers can’t use the local DNS nameserver. Instead, Docker defaults to using an external nameserver.

To avoid this warning, you can specify a DNS server for use by Docker containers. Or, you can disable dnsmasq in NetworkManager. Though, disabling dnsmasq might make DNS resolution slower on some networks.

To specify a DNS server for use by Docker:

  1. Log into Ubuntu as a user with sudo privileges.

  2. Open the /etc/default/docker file for editing.

    $ sudo nano /etc/default/docker
    
  3. Add a setting for Docker.

    DOCKER_OPTS="--dns 8.8.8.8"
    

    Replace 8.8.8.8 with a local DNS server such as 192.168.1.1. You can also specify multiple DNS servers. Separated them with spaces, for example:

    --dns 8.8.8.8 --dns 192.168.1.1
    

    Warning: If you’re doing this on a laptop which connects to various networks, make sure to choose a public DNS server.

  4. Save and close the file.

  5. Restart the Docker daemon.

    $ sudo restart docker
    

   

Or, as an alternative to the previous procedure, disable dnsmasq in NetworkManager (this might slow your network).

  1. Open the /etc/NetworkManager/NetworkManager.conf file for editing.

    $ sudo nano /etc/NetworkManager/NetworkManager.conf
    
  2. Comment out the dns=dsnmasq line:

    dns=dnsmasq
    
  3. Save and close the file.

  4. Restart both the NetworkManager and Docker.

    $ sudo restart network-manager $ sudo restart docker
    

Configure Docker to start on boot

Ubuntu uses systemd as its boot and service manager 15.04 onwards and upstart for versions 14.10 and below.

For 15.04 and up, to configure the docker daemon to start on boot, run

$ sudo systemctl enable docker

 

For 14.10 and below the above installation method automatically configures upstart to start the docker daemon on boot

Upgrade Docker

To install the latest version of Docker with curl:

$ curl -sSL https://get.docker.com/ | sh

Uninstallation

To uninstall the Docker package:

$ sudo apt-get purge docker-engine

To uninstall the Docker package and dependencies that are no longer needed:

$ sudo apt-get autoremove --purge docker-engine

The above commands will not remove images, containers, volumes, or user created configuration files on your host. If you wish to delete all images, containers, and volumes run the following command:

$ rm -rf /var/lib/docker

You must delete the user created configuration files manually.

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