| 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](#installing-docker-on-ubuntu).
## 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 `wget` installed.
$ which wget
If `wget` isn't installed, install it after updating your manager:
$ sudo apt-get update
$ sudo apt-get install wget
3. Get the latest Docker package.
$ wget -qO- 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:
>
> $ wget -qO- https://get.docker.com/gpg | sudo apt-key add -
4. 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](#create-a-docker-group)
* [Adjust memory and swap accounting](#adjust-memory-and-swap-accounting)
* [Enable UFW forwarding](#enable-ufw-forwarding)
* [Configure a DNS server for use by Docker](#configure-a-dns-server-for-docker)
* [Configure Docker to start on boot](#configure-docker-to-start-on-boot)
### 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*](/articles/security/#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.
3. 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. To
enable these 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)](https://help.ubuntu.com/community/UFW)
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 `wget`:
$ wget -qO- 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.