Friday 24 August 2018

Get Docker for Debian Up and Running

Estimated reading time: 9 minutes
To get started with Docker on Debian, make sure you meet the prerequisites, then install Docker.

Prerequisites

Docker EE customers

Docker EE is not supported on Debian. For a list of supported operating systems and distributions for different Docker editions, see Docker variants.

OS requirements

To install Docker, you need the 64-bit version of one of these Debian or Raspbian versions:

  • Stretch (testing)
  • Jessie 8.0 (LTS) / Raspbian Jessie
  • Wheezy 7.7 (LTS)
Docker CE is supported on both x86_64 and armhf architectures for Jessie and Stretch.

Uninstall old versions

Older versions of Docker were called docker or docker-engine. If these are installed, uninstall them:

$ sudo apt-get remove docker docker-engine
It’s OK if apt-get reports that none of these packages are installed.

The contents of /var/lib/docker/, including images, containers, volumes, and networks, are preserved. The Docker CE package is now called docker-ce.

Extra steps for Wheezy 7.7

  • You need at least version 3.10 of the Linux kernel. Debian Wheezy ships with version 3.2, so you may need to update the kernel. To check your kernel version:

    $ uname -r
  • Enable the backports repository. See the Debian documentation.

Install Docker CE

You can install Docker CE in different ways, depending on your needs:

  • Most users set up Docker’s repositories and install from them, for ease of installation and upgrade tasks. This is the recommended approach.
  • Some users download the DEB package and install it manually and manage upgrades completely manually. This is useful in situations such as installing Docker on air-gapped systems with no access to the internet.

Install using the repository

Before you install Docker CE for the first time on a new host machine, you need to set up the Docker repository. Afterward, you can install and update Docker from the repository.

Set up the repository

  1. Install packages to allow apt to use a repository over HTTPS:

    Jessie or Stretch:

    $ sudo apt-get install \
         apt-transport-https \
         ca-certificates \
         curl \
         gnupg2 \
         software-properties-common
    Wheezy:

    $ sudo apt-get install \
         apt-transport-https \
         ca-certificates \
         curl \
         python-software-properties
  2. Add Docker’s official GPG key:

    $ curl -fsSL https://download.docker.com/linux/debian/gpg | sudo apt-key add -
    Verify that the key ID is 9DC8 5822 9FC7 DD38 854A E2D8 8D81 803C 0EBF CD88.

    $ sudo apt-key fingerprint 0EBFCD88

    pub   4096R/0EBFCD88 2017-02-22
          Key fingerprint = 9DC8 5822 9FC7 DD38 854A  E2D8 8D81 803C 0EBF CD88
    uid                  Docker Release (CE deb) <docker@docker.com>
    sub   4096R/F273FCD8 2017-02-22
  3. Use the following command to set up the stable repository. You always need the stable repository, even if you want to install edge builds as well.

    Note: The lsb_release -cs sub-command below returns the name of your Debian distribution, such as jessie.


    To also add the edge repository, add edge after stable on the last line of the command.

    amd64:

    $ sudo add-apt-repository \
       "deb [arch=amd64] https://download.docker.com/linux/debian \
       $(lsb_release -cs) \
       stable"
    armhf:

    You can choose between two methods for armhf. You can use the same method as Debian, setting up the repository and using apt-get install, or you can use a convenience script, which requires privileged access, but sets up the repository for you and installs the packages for Bash auto-completion.
    • Setting up the repository directly:

      $ echo "deb [arch=armhf] https://apt.dockerproject.org/repo \
          raspbian-jessie main" | \
          sudo tee /etc/apt/sources.list.d/docker.list
    • Using the convenience script:

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

      $ sudo bash ./install.sh
      Warning: Always audit scripts downloaded from the internet before running them locally.


      If you use this method, Docker is installed and starts automatically. Skip to step 4 below.
  4. Wheezy only: The version of add-apt-repository on Wheezy adds a deb-src repository that does not exist. You need to comment out this repository or running apt-get update will fail. Edit /etc/apt/sources.list. Find the line like the following, and comment it out or remove it:

    deb-src [arch=amd64] https://download.docker.com/linux/debian wheezy stable
    Save and exit the file.

    Learn about stable and edge channels.

Install Docker CE

NOTE: Docker CE is not available on raspbian-jessie, scroll down to follow the Raspian steps.

  1. Update the apt package index.

    $ sudo apt-get update
  2. Install the latest version of Docker, or go to the next step to install a specific version. Any existing installation of Docker is replaced.

    Use this command to install the latest version of Docker:

    $ sudo apt-get install docker-ce
    Warning: If you have multiple Docker repositories enabled, installing or updating without specifying a version in the apt-get install or apt-get update command will always install the highest possible version, which may not be appropriate for your stability needs.

  3. On production systems, you should install a specific version of Docker instead of always using the latest. This output is truncated. List the available versions:

    $ apt-cache madison docker-ce

    docker-ce | 17.03.0~ce-0~debian-jessie | https://download.docker.com/linux/debian jessie/stable amd64 Packages
    The contents of the list depend upon which repositories are enabled, and will be specific to your version of Debian (indicated by the jessie suffix on the version, in this example). Choose a specific version to install. The second column is the version string. The third column is the repository name, which indicates which repository the package is from and by extension its stability level. To install a specific version, append the version string to the package name and separate them by an equals sign (=):

    $ sudo apt-get install docker-ce=<VERSION_STRING>
    The Docker daemon starts automatically.
  4. Verify that Docker CE is installed correctly by running the hello-world image.

    $ sudo docker run hello-world
    This command downloads a test image and runs it in a container. When the container runs, it prints an informational message and exits.
Docker CE is installed and running. You need to use sudo to run Docker commands. Continue to Linux postinstall to allow non-privileged users to run Docker commands and for other optional configuration steps.

Upgrade Docker CE

To upgrade Docker, first run sudo apt-get update, then follow the installation instructions, choosing the new version you want to install.

Install on Raspian (Raspberry Pi)

Warning: This isn’t necessary if you used the recommended bash $ curl -sSL https://get.docker.com | sh command!

Once you have added the Docker repo to /etc/apt/sources.list.d/, you should see docker.list if you:

$ ls /etc/apt/sources.list.d/
And the contents of the docker.list should read:

deb [arch=armhf] https://apt.dockerproject.org/repo raspbian-jessie main

If you don’t see that in docker.list, then either comment the line out, or rm the docker.list file.

Once you have verified that you have the correct repository, you may continue installing Docker.

  1. Update the apt package index.

    $ sudo apt-get update
  2. Install the latest version of Docker, or go to the next step to install a specific version. Any existing installation of Docker is replaced.

    Use this command to install the latest version of Docker:

    $ sudo apt-get install docker
    NOTE: By default, Docker on Raspian is Docker Community Edition, so there is no need to specify docker-ce.


    NOTE: If bash $ curl -sSL https://get.docker.com | sh isn’t used, then docker won’t have auto-completion! You’ll have to add it manually.

  3. Verify that Docker is installed correctly by running the hello-world image.

    $ sudo docker run hypriot/armhf-hello-world
    This command downloads a test image and runs it in a container. When the container runs, it prints an informational message and exits.

Install from a package

If you cannot use Docker’s repository to install Docker CE, you can download the .deb file for your release and install it manually. You will need to download a new file each time you want to upgrade Docker.

  1. Go to https://download.docker.com/linux/debian/dists/, choose your Debian version, browse to stable/pool/stable/, choose either amd64 or armhf,and download the .deb file for the Docker version you want to install and for your version of Debian.

    Note: To install an edge package, change the word stable in the URL to edge. Learn about stable and edge channels.

  2. Install Docker CE, changing the path below to the path where you downloaded the Docker package.

    $ sudo dpkg -i /path/to/package.deb
    The Docker daemon starts automatically.
  3. Verify that Docker CE is installed correctly by running the hello-world image.

    $ sudo docker run hello-world
    This command downloads a test image and runs it in a container. When the container runs, it prints an informational message and exits.
Docker CE is installed and running. You need to use sudo to run Docker commands. Continue to Post-installation steps for Linux to allow non-privileged users to run Docker commands and for other optional configuration steps.

Upgrade Docker

To upgrade Docker, download the newer package file and repeat the installation procedure, pointing to the new file.

Uninstall Docker

  1. Uninstall the Docker package:

    $ sudo apt-get purge docker-ce
  2. Images, containers, volumes, or customized configuration files on your host are not automatically removed. To delete all images, containers, and volumes:

    $ sudo rm -rf /var/lib/docker
You must delete any edited configuration files manually.

Next steps


Does RHEL 7 support online resize of disk partitions?

Environment

  • Red Hat Enterprise Linux 7

Issue

  • Both Xen and KVM support online resize of the virtual block devices that the virtual machines use.
  • Unfortunately, since the partitions in the boot virtual block device are already in use, those can't be modified online and the virtual machine won't pick up the changes on the boot virtual block device without a reboot.
  • We are looking for ability to dynamically increase a partitioned volume, is it possible to resize the disk partitions online in RHEL 7?
  • We are unable to dynamically increase a SAN attached volume without taking the volume offline. When will this feature to Support online resize of disk partitions be available?

Resolution

The ability to resize a Logical Volume and filesystem has long been provided by Logical Volume Manager (LVM) by simply using the entire block device (/dev/sdx for example) as a Physical Volume in the LVM Volume Group. There is no need for the old style of partition. This would allow the Logical Volume and filesystem to easily be expanded.
As to older style partitions, this feature has been added in RHEL 7 current release with a feature request (RFE has been filed to add support for online resize of disk partitions to RHEL 7 in private Red Hat Bugzilla 853105). With this feature, it's possible to resize the disk partitions online in RHEL 7.

Warning: Online partition table resizing is not a recommended process mostly because the underlying layer of an active logical volume or filesystem that relies on that information is being modified. While it is possible to perform online partition resize operation, it is not recommended simply from a data integrity standpoint and not because it's not possible.

  • In order to resize online a partition which is in use please observe the following steps:
# fdisk -l /dev/vda

Disk /dev/vda: 32.2 GB, 32212254720 bytes, 62914560 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x000db7e6

   Device Boot      Start         End      Blocks   Id  System
/dev/vda1   *        2048     1026047      512000   83  Linux
/dev/vda2         1026048    28289023    13631488   8e  Linux LVM

# cat /proc/partitions 
major minor  #blocks  name

 252        0   31457280 vda
 252        1     512000 vda1
 252        2   13631488 vda2
  11        0    1048575 sr0
 253        0   10240000 dm-0
 253        1    2129920 dm-1

# pvs
  PV         VG          Fmt  Attr PSize  PFree
  /dev/vda2  rhel_vm-205 lvm2 a--  13.00g 1.20g
  • Modify the on-disk partition table as usual (e.g. by using fdisk command).
    • Delete the partition:
      Command (m for help): d
      Partition number (1,2, default 2): 2
      Partition 2 is deleted
      
    • Re-create the partition with the new size:
      Command (m for help): n
      Partition type:
         p   primary (1 primary, 0 extended, 3 free)
         e   extended
      Select (default p): p
      Partition number (2-4, default 2): 2
      First sector (1026048-62914559, default 1026048): 
      Using default value 1026048
      Last sector, +sectors or +size{K,M,G} (1026048-62914559, default 62914559): +18G
      Partition 2 of type Linux and of size 18 GiB is set
      
      Command (m for help): t
      Partition number (1,2, default 2): 2
      Hex code (type L to list all codes): 8e
      Changed type of partition 'Linux' to 'Linux LVM'
      
      Command (m for help): p
      
      Disk /dev/vda: 32.2 GB, 32212254720 bytes, 62914560 sectors
      Units = sectors of 1 * 512 = 512 bytes
      Sector size (logical/physical): 512 bytes / 512 bytes
      I/O size (minimum/optimal): 512 bytes / 512 bytes
      Disk label type: dos
      Disk identifier: 0x000db7e6
      
         Device Boot      Start         End      Blocks   Id  System
      /dev/vda1   *        2048     1026047      512000   83  Linux
      /dev/vda2         1026048    38774783    18874368   8e  Linux LVM
      
    • Commit changes to on-disk partition table:
      Command (m for help): w
      The partition table has been altered!
      
      Calling ioctl() to re-read partition table.
      
      WARNING: Re-reading the partition table failed with error 16: Device or resource busy.
      The kernel still uses the old table. The new table will be used at
      the next reboot or after you run partprobe(8) or kpartx(8)
      Syncing disks.
      
    • While on-disk partition table has been updated, observe that on-memory kernel partition table has not:
      # partprobe 
      Error: Partition(s) 2 on /dev/vda have been written, but we have been unable to inform the kernel of the change, probably because it/they are in use.  As a result, the old partition(s) will remain in use.  You should reboot now before making further changes.
      
      # cat /proc/partitions | grep vd
       252        0   31457280 vda
       252        1     512000 vda1
       252        2   13631488 vda2
      
  • Execute partx (provided by util-linux package) with --update option on the block device to update the in-memory kernel partition table from the on-disk partition table:
    # partx -u /dev/vda
    
  • Verify that in-memory kernel partition table has been updated with the new size:
    # cat /proc/partitions | grep vd
     252        0   31457280 vda
     252        1     512000 vda1
     252        2   18874368 vda2
    
  • Proceed with any further steps, in this example by extending the PV on the partition:
    # pvresize /dev/vda2
      Physical volume "/dev/vda2" changed
      1 physical volume(s) resized / 0 physical volume(s) not resized
    
    # pvs
      PV         VG          Fmt  Attr PSize  PFree
      /dev/vda2  rhel_vm-205 lvm2 a--  18.00g 6.20g
    

Root Cause

  • Changes to allow online resizing of in-use partitions are required in both kernel and userland.
    • RHEL7 kernels include the required changes to BLKPG ioctl from block: add partition resize function to blkpg ioctl to support BLKPG_RESIZE_PARTITION operation.
    • RHEL7 util-linux package includes partx and resizepart binaries, currently the only userland commands that support BLKPG_RESIZE_PARTITION operation of BLKPG ioctl.

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