Ubuntu

Docker is supported on the following versions of Ubuntu:

Please read Docker and UFW, if you plan to use UFW (Uncomplicated Firewall)

Ubuntu Trusty 14.04 (LTS) (64-bit)

Ubuntu Trusty comes with a 3.13.0 Linux kernel, and a docker.io package which installs Docker 0.9.1 and all its prerequisites from Ubuntu's repository.

Note: Ubuntu (and Debian) contain a much older KDE3/GNOME2 package called docker, so the package and the executable are called docker.io.

Installation

To install the latest Ubuntu package (may not be the latest Docker release):

$ sudo apt-get update
$ sudo apt-get install docker.io
$ sudo ln -sf /usr/bin/docker.io /usr/local/bin/docker
$ sudo sed -i '$acomplete -F _docker docker' /etc/bash_completion.d/docker.io

If you'd like to try the latest version of Docker:

First, check that your APT system can deal with https URLs: the file /usr/lib/apt/methods/https should exist. If it doesn't, you need to install the package apt-transport-https.

[ -e /usr/lib/apt/methods/https ] || {
  apt-get update
  apt-get install apt-transport-https
}

Then, add the Docker repository key to your local keychain.

$ sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 36A1D7869245C8950F966E92D8576A8BA88D21E9

Add the Docker repository to your apt sources list, update and install the lxc-docker package.

You may receive a warning that the package isn't trusted. Answer yes to continue installation.

$ sudo sh -c "echo deb https://get.docker.io/ubuntu docker main\
> /etc/apt/sources.list.d/docker.list"
$ sudo apt-get update
$ sudo apt-get install lxc-docker

Note:

There is also a simple curl script available to help with this process.

$ curl -sSL https://get.docker.io/ubuntu/ | sudo sh

To verify that everything has worked as expected:

$ sudo docker run -i -t ubuntu /bin/bash

Which should download the ubuntu image, and then start bash in a container.

Ubuntu Precise 12.04 (LTS) (64-bit)

This installation path should work at all times.

Dependencies

Linux kernel 3.8

Due to a bug in LXC, Docker works best on the 3.8 kernel. Precise comes with a 3.2 kernel, so we need to upgrade it. The kernel you'll install when following these steps comes with AUFS built in. We also include the generic headers to enable packages that depend on them, like ZFS and the VirtualBox guest additions. If you didn't install the headers for your "precise" kernel, then you can skip these headers for the "raring" kernel. But it is safer to include them if you're not sure.

Please read the installation instructions for backported kernels at Ubuntu.org to understand why you also need to install the Xorg packages when running Docker on a machine with a graphical environment like Unity. LTS Enablement Stack refer to note 5 under each version.

# install the backported kernel
$ sudo apt-get update
$ sudo apt-get install linux-image-generic-lts-raring linux-headers-generic-lts-raring

# install the backported kernel and xorg if using Unity/Xorg
$ sudo apt-get install --install-recommends linux-generic-lts-raring xserver-xorg-lts-raring libgl1-mesa-glx-lts-raring

# reboot
$ sudo reboot

Installation

Warning: These instructions have changed for 0.6. If you are upgrading from an earlier version, you will need to follow them again.

Docker is available as a Debian package, which makes installation easy. See the Mirrors section below if you are not in the United States. Other sources of the Debian packages may be faster for you to install.

First, check that your APT system can deal with https URLs: the file /usr/lib/apt/methods/https should exist. If it doesn't, you need to install the package apt-transport-https.

[ -e /usr/lib/apt/methods/https ] || {
  apt-get update
  apt-get install apt-transport-https
}

Then, add the Docker repository key to your local keychain.

$ sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 36A1D7869245C8950F966E92D8576A8BA88D21E9

Add the Docker repository to your apt sources list, update and install the lxc-docker package.

You may receive a warning that the package isn't trusted. Answer yes to continue installation.

$ sudo sh -c "echo deb https://get.docker.io/ubuntu docker main\
> /etc/apt/sources.list.d/docker.list"
$ sudo apt-get update
$ sudo apt-get install lxc-docker

Note:

There is also a simple curl script available to help with this process.

$ curl -sSL https://get.docker.io/ubuntu/ | sudo sh

Now verify that the installation has worked by downloading the ubuntu image and launching a container.

$ sudo docker run -i -t ubuntu /bin/bash

Type exit to exit

Done!, continue with the User Guide.

Ubuntu Raring 13.04 and Saucy 13.10 (64 bit)

These instructions cover both Ubuntu Raring 13.04 and Saucy 13.10.

Dependencies

Optional AUFS filesystem support

Ubuntu Raring already comes with the 3.8 kernel, so we don't need to install it. However, not all systems have AUFS filesystem support enabled. AUFS support is optional as of version 0.7, but it's still available as a driver and we recommend using it if you can.

To make sure AUFS is installed, run the following commands:

$ sudo apt-get update
$ sudo apt-get install linux-image-extra-`uname -r`

Installation

Docker is available as a Debian package, which makes installation easy.

Warning: Please note that these instructions have changed for 0.6. If you are upgrading from an earlier version, you will need to follow them again.

First add the Docker repository key to your local keychain.

$ sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 36A1D7869245C8950F966E92D8576A8BA88D21E9

Add the Docker repository to your apt sources list, update and install the lxc-docker package.

$ sudo sh -c "echo deb http://get.docker.io/ubuntu docker main\
> /etc/apt/sources.list.d/docker.list"
$ sudo apt-get update
$ sudo apt-get install lxc-docker

Now verify that the installation has worked by downloading the ubuntu image and launching a container.

$ sudo docker run -i -t ubuntu /bin/bash

Type exit to exit

Done!, now continue with the User Guide.

Giving non-root access

The docker daemon always runs as the root user, and since Docker version 0.5.2, 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 so, by default, you can access it with sudo.

Starting in version 0.5.3, if you (or your Docker installer) create a Unix group called docker and add users to it, then the docker daemon will make the ownership of the Unix socket read/writable by the docker group when the daemon starts. The docker daemon must always run as the root user, but if you run the docker client as a user in the docker group then you don't need to add sudo to all the client commands. From Docker 0.9.0 you can use the -G flag to specify an alternative group.

Warning: The docker group (or the group specified with the -G flag) is root-equivalent; see Docker Daemon Attack Surface details.

Example:

# Add the docker group if it doesn't already exist.
$ sudo groupadd docker

# Add the connected user "${USER}" to the docker group.
# Change the user name to match your preferred user.
# You may have to logout and log back in again for
# this to take effect.
$ sudo gpasswd -a ${USER} docker

# Restart the Docker daemon.
# If you are in Ubuntu 14.04, use docker.io instead of docker
$ sudo service docker restart

Upgrade

To install the latest version of docker, use the standard apt-get method:

# update your sources list
$ sudo apt-get update

# install the latest
$ sudo apt-get install lxc-docker

Memory and Swap Accounting

If you want to enable memory and swap accounting, you must add the following command-line parameters to your kernel:

cgroup_enable=memory swapaccount=1

On systems using GRUB (which is the default for Ubuntu), you can add those parameters by editing /etc/default/grub and extending GRUB_CMDLINE_LINUX. Look for the following line:

GRUB_CMDLINE_LINUX=""

And replace it by the following one:

GRUB_CMDLINE_LINUX="cgroup_enable=memory swapaccount=1"

Then run sudo update-grub, and reboot.

These parameters will help you get rid of the following warnings:

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

Troubleshooting

On Linux Mint, the cgroup-lite and apparmor packages are not installed by default. Before Docker will work correctly, you will need to install this via:

$ sudo apt-get update && sudo apt-get install cgroup-lite apparmor

Docker and UFW

Docker uses a bridge to manage container networking. By default, UFW drops all forwarding traffic. As a result you will need to enable UFW forwarding:

$ sudo nano /etc/default/ufw

# Change:
# DEFAULT_FORWARD_POLICY="DROP"
# to
DEFAULT_FORWARD_POLICY="ACCEPT"

Then reload UFW:

$ sudo ufw reload

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 allow incoming connections on the Docker port (default 2375):

$ sudo ufw allow 2375/tcp

Docker and local DNS server warnings

Systems which are running Ubuntu or an Ubuntu derivative on the desktop will use 127.0.0.1 as the default nameserver in /etc/resolv.conf. NetworkManager 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 these desktop machines, users will see a 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]

This warning is shown because the containers can't use the local DNS nameserver and Docker will default to using an external nameserver.

This can be worked around by specifying a DNS server to be used by the Docker daemon for the containers:

$ sudo nano /etc/default/docker
---
# Add:
DOCKER_OPTS="--dns 8.8.8.8"
# 8.8.8.8 could be replaced with a local DNS server, such as 192.168.1.1
# multiple DNS servers can be specified: --dns 8.8.8.8 --dns 192.168.1.1

The Docker daemon has to be restarted:

$ sudo restart docker

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

An alternative solution involves disabling dnsmasq in NetworkManager by following these steps:

$ sudo nano /etc/NetworkManager/NetworkManager.conf
----
# Change:
dns=dnsmasq
# to
#dns=dnsmasq

NetworkManager and Docker need to be restarted afterwards:

$ sudo restart network-manager
$ sudo restart docker

Warning: This might make DNS resolution slower on some networks.

Mirrors

You should ping get.docker.io and compare the latency to the following mirrors, and pick whichever one is best for you.

Yandex

Yandex in Russia is mirroring the Docker Debian packages, updating every 6 hours. Substitute http://mirror.yandex.ru/mirrors/docker/ for http://get.docker.io/ubuntu in the instructions above. For example:

$ sudo sh -c "echo deb http://mirror.yandex.ru/mirrors/docker/ docker main\
> /etc/apt/sources.list.d/docker.list"
$ sudo apt-get update
$ sudo apt-get install lxc-docker