Installing docker on CentOS

Docker Install via Docker’s repository

1. Install required packages

   sudo yum install -y yum-utils
   

2. Set up the stable repository:

   sudo yum-config-manager \
   --add-repo \
   https://download.docker.com/linux/centos/docker-ce.repo
   

3. Install the latest version of Docker CE and containerd:

   sudo yum install docker-ce docker-ce-cli containerd.io
   

4. Start Docker (Docker is installed but not started):

   sudo docker run hello-world
   

5. Post install

   1. Create the docker group:

      sudo groupadd docker
      

   2. Add your user to the docker group:

      sudo usermod -aG docker $USER
      

   3. Log out and log back in so that your group membership is re-evaluated.

      If testing on a virtual machine, it may be necessary to restart the virtual machine for changes to take effect.

   4. Verify that you can run docker commands without sudo:

      docker run hello-world
      

Configure Docker with the overlay2 storage driver

1. Prerequisites

   1. Verify you CentOS is uing 3.10.0-514 of the Linux kernel or higher

      uname -s -r
      

   # Determine filesystem type

   df -TH /home
   

   1. If filesystem is xfs:

      1. Verify that the ftype option is set to 1.

         xfs_info /home
         

      2. If ftype is set to 0, then format the xfs filesystem correctly, use the flag -n ftype=1

         The overlay2 driver is supported on xfs backing filesystems, but only with d_type=true enabled. (d_type == “directory entry type”; used by Linux kernel to describe the information of a directory on the filesystem)

      3. Easier option, if available, is to configure Docker to point to an ext4 mounted filesystem.

         Note

         You may format the filesystem and mount it into /var/lib/docker (the default docker daemon (root) dir) or with a name of your liking.

         e.g. filesystem: /dev/sdb1 mounted on: /home2 and docker root dir set to:/home2/docker-base/docker

         Make sure add this mount to /etc/fstab to make it permanent.

         e.g. entry in /etc/fstab:/dev/sdb1 /home2 ext4 defaults 0 0

      4. If filesystem is ext4, nothing more to do.

2. Configuration

   1. Stop Docker

      sudo systemctl stop docker
      

   2. If necessary, copy the contents of the docker root dir(by default:/var/lib/docker) to a temporary location.

      cp -au /var/lib/docker /var/lib/docker.back
      

   3. Edit /etc/docker/daemon.json.

      If it does not yet exist, create it. Assuming that the file was empty, add the following contents.

      {
      "storage-driver": "overlay2"
      }
      

      Note

      If you wish to change the default docker root dir (recommended, especially if an ext4 filesystem is available), then also add the new path to /etc/docker/daemon.json as follows:

      {
      "data-root":"/new/data/root/path"
      }
      # e.g.
      {
      "data-root":"/home2/docker-base/docker"
      }
      

   4. start Docker

      sudo systemctl start docker
      

   5. Verify that the daemon is using the overlay2 storage driver.

      Use the docker info command and look for Storage Driver and Backing filesystem.

      $ docker info
      
      # e.g. xfs file system, default Docker Root Dir
      
          Containers: 0
          Images: 0
          Storage Driver: overlay2
          Backing Filesystem: xfs
          Supports d_type: true
          Native Overlay Diff: true
          <output truncated>
          Docker Root Dir:/etc/lib/docker
          <output truncated>
      
      # e.g. ext4 filesystem,
      
          Containers: 0
          Images: 0
          Storage Driver: overlay2
          Backing Filesystem: extfs
          Supports d_type: true
          Native Overlay Diff: true
          <output truncated>
          Docker Root Dir:/home2/docker-base/docker
          <output truncated>