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Check your current Linux version with uname -r. You should see something like 3.10.[alphanumeric string].x86_64.

Debian and Ubuntu

Docker runs on:

• Ubuntu Xenial 16.04 LTS
• Ubuntu Wily 15.10
• Ubuntu Trusty 14.04 LTS
• Ubuntu Precise 12.04 LTS
• Debian testing stretch
• Debian 8.0 Jessie
• Debian 7.0 Wheezy (you must enable backports)

Debian Wheezy

If so, you need to enable backports (if not, ignore this section):

1. Log into the system and open a terminal with sudo or root privileges (or run sudo -i from your terminal).
2. Open /etc/apt/sources.list.d/backports.list with your favorite text editor (if the file does not exist, create it).
3. Remove existing entries.
4. Add an entry for backports on Debian Wheezy:
   

    deb http://http.debian.net/debian wheezy-backports main
   

5. Update your packages:

    apt-get update -y
   

Ubuntu Precise 12.04

If so, you need to make sure you have the 3.13 kernel version. You must upgrade your kernel:

1. Open a terminal on your system.
2. Update aptitude:
   

    sudo apt-get update -y
   

3. Install the additional packages:
   

    sudo apt-get install -y linux-image-generic-lts-trusty linux-headers-generic-lts-trusty
   

4. On a graphical Ubuntu environment, you need to additionally run the following:
   

    sudo apt-get install -y xserver-xorg-lts-trusty libgl1-mesa-glx-lts-trusty
   

5. Reboot your system:
   

    sudo reboot
   

Update Aptitude

1. Log onto your system with a user with sudo privileges.
2. Open a terminal window.
3. Purge the older repositories:
   

    sudo apt-get purge -y lxc-docker* && sudo apt-get -y purge docker.io*
   

4. Update your packages, making sure apt works with https and the server has CA certificates:
   

    sudo apt-get update -y && sudo apt-get install -y apt-transport-https ca-certificates
   

5. Get the new GPG key:
   

    sudo apt-key adv --keyserver hkp://p80.pool.sks-keyservers.net:80 --recv-keys 58118E89F3A912897C070ADBF76221572C52609D
   

6. Open or create the file /etc/apt/sources.list.d/docker.list in your favorite text editor (you need sudo or root for this).

7. Add an entry for your OS

   Version	Source
   Ubuntu Precise 12.04 LTS	deb https://apt.dockerproject.org/repo ubuntu-precise main
   Ubuntu Trusty 14.04 LTS	deb https://apt.dockerproject.org/repo ubuntu-trusty main
   Ubuntu Wily 15.10 LTS	deb https://apt.dockerproject.org/repo ubuntu-wily main
   Ubuntu Xenial 16.04 LTS	deb https://apt.dockerproject.org/repo ubuntu-xenial main
   Debian Wheezy	deb https://apt.dockerproject.org/repo debian-wheezy main
   Debian Jessie	deb https://apt.dockerproject.org/repo debian-jessie main
   Debian Stretch/Sid	deb https://apt.dockerproject.org/repo debian-stretch main

8. Save and close the file.
9. Update Aptitude again:
   

    sudo apt-get update -y
   

10. Verify Aptitude pulls from the right repository:
    

    sudo apt-cache policy docker-engine
    

Install Docker

If you use Ubuntu Trusty, Wily, or Xenial, install the linux-image-extra kernel package:

sudo apt-get update -y && sudo apt-get install -y linux-image-extra-$(uname -r)

1. Install Docker:
   

   sudo apt-get install docker-engine -y
   

2. Start Docker:
   

    sudo service docker start
   

3. Verify Docker:
   

    sudo docker run hello-world
   

The Docker Group

If you prefer, you can set up a docker group to run Docker (instead of root). However, as docker must have sudo access, docker receives the same access as root.

1. Run the following command to create a Docker group on Ubuntu:
   

    sudo groupadd docker && sudo usermod -aG docker ubuntu
   

2. Log out and back in.

3. Run the following command to create a Docker group on Debian:
   

    sudo groupadd docker && sudo gpasswd -a ${USER} docker && sudo service docker restart
   

   You may specify a user instead of ${USER} if you prefer.

4. Verify a successful Docker installation:
   

    docker run hello-world
   

Red Hat Enterprise Linux (RHEL) and CentOS

Docker runs on RHEL 7 and CentOS 7.

Install Docker

Install with Yum

1. Log into your system as a user with sudo privileges.
2. Update your system: sudo yum update -y.
3. Add the yum repo (use the code below for both RHEL 7 and CentOS 7):
   

    $ sudo tee /etc/yum.repos.d/docker.repo <<-'EOF'
    [dockerrepo]
    name=Docker Repository
    baseurl=https://yum.dockerproject.org/repo/main/centos/7/
    enabled=1
    gpgcheck=1
    gpgkey=https://yum.dockerproject.org/gpg
    EOF
   

4. Install Docker:

    sudo yum install docker-engine -y
   

5. Start Docker:

    sudo service docker start
   

6. Verify Docker:

    sudo docker run hello-world
   

Install with the Docker Installation Script

1. Log into your system as a user with sudo privileges.
2. Update your system:

    sudo yum update -y
   

3. Run Docker’s installation script:

    curl -fsSL https://get.docker.com | sh;
   

   This script adds the docker.repo repository and installs Docker.

4. Start Docker:

    sudo service docker start
   

5. Verify Docker:

    sudo docker run hello-world
   

The Docker Group

If you prefer, you can set up a docker group to run Docker (instead of root). However, as docker must have sudo access, docker receives the same access as root.

1. Run the following command to create a Docker group and add your user to the group (replace USERNAME with your username):
   

    sudo groupadd docker && sudo usermod -aG docker USERNAME
   

2. Log out and back in.
3. Verify Docker works without sudo:

    docker run hello-world
   

Start Docker at Boot

Run one of the following:

• sudo chkconfig docker on
• sudo systemctl enable docker

Common Issues

Note: Members in the docker group have root privileges. Hardening Docker is covered in a future tutorial.

Ubuntu

Ubuntu Utopic 14.10 and 15.05 exist in Docker’s apt repository without official support. Upgrade to 15.10 or [preferably] 16.04. If you use Ubuntu 12.04, you need to update your kernel.

Debian

If you run Debian Wheezy, you need to update the sources with backports.

“Cannot connect to the Docker daemon. Is ‘docker daemon’ running on this host?”

If you get this error, you need to unset DOCKER_HOST; run unset DOCKER_HOST to clear the variable.