adevur/centos-8 Docker Image

Description

This is an unofficial Docker image with CentOS 8.0 installed. This image should be very similar to registry.redhat.io/ubi8: the main two differences are that ubi8 is based on Red Hat Enterprise Linux 8.0, while adevur/centos-8 is based on CentOS 8.0; and that ubi8 has access to a very limited package repository of RHEL 8.0, while adevur/centos-8 has access to the entire package repository of CentOS 8.0 (i.e. Base, Extras and AppStream).

Tags

• latest: this is similar to Red Hat's ubi8.

  NOTE: tag latest will automatically download the correct architecture for your device (i.e. amd64, arm64v8 or ppc64le); however, you can also use these tags to download a specific architecture: latest-amd64, latest-arm64v8 and latest-ppc64le.

• init: this is similar to Red Hat's ubi8-init.

  NOTE: tag init will automatically download the correct architecture for your device (i.e. amd64, arm64v8 or ppc64le); however, you can also use these tags to download a specific architecture: init-amd64, init-arm64v8 and init-ppc64le.

• systemd: this is similar to CentOS centos/systemd.

  NOTE: tag systemd will automatically download the correct architecture for your device (i.e. amd64, arm64v8 or ppc64le); however, you can also use these tags to download a specific architecture: systemd-amd64, systemd-arm64v8 and systemd-ppc64le.

Usage

Tag latest

In order to use the latest tag, just type:

docker run -it --rm adevur/centos-8:latest /bin/bash

And you will get a bash terminal inside the container. You can check that you're running CentOS 8 by typing:

cat /etc/redhat-release
# EXPECTED OUTPUT: CentOS Linux release 8.0.1905 (Core)

Tag init

Have a look at Red Hat's documentation for registry.redhat.io/ubi8-init image. adevur/centos-8:init should work the same as ubi8-init.

Tag systemd

Have a look at CentOS documentation for docker.io/centos/systemd image. adevur/centos-8:systemd should work the same as centos/systemd.

You can use this tag to run systemd services in the background. For example:

# let's start the container in the background
docker run --privileged -v /sys/fs/cgroup:/sys/fs/cgroup:ro -d --name my-container adevur/centos-8:systemd

# let's start a bash shell inside the running container
docker exec -it my-container /bin/bash

# now that we're inside the container, let's install ssh
yum clean all && yum -y install openssh-server && yum clean all

# now we can start the systemd service of ssh
systemctl start sshd.service

# let's check that ssh is running
systemctl status sshd.service

Building

• In order to build tag latest, you need:

  1. A rootfs tarball that contains the filesystem. I've generated the tarball already (you can find it at ./tag-latest/centos-8-adevur0-$ARCH.tar.xz; replace $ARCH with amd64, aarch64 or ppc64le), but you can also generate it by yourself.

  2. A kickstart script, in case you want to build the tarball yourself. I've already written a kickstart script (you can find it at ./tag-latest/centos-8-adevur0-$ARCH.ks; replace $ARCH with amd64, aarch64 or ppc64le). You can write one yourself too, if you want to customize something.

  3. A Dockerfile (you can find it at ./tag-latest/Dockerfile.$ARCH; replace $ARCH with amd64, arm64v8 or ppc64le).

• In order to build adevur/centos-8:init and adevur/centos-8:systemd, you just need their Dockerfiles.

Create the Docker image itself

In case you already have the tarball, you can simply type:

# building latest tag (for amd64 arch)
docker build --tag local/centos-8:latest --file ./tag-latest/Dockerfile.amd64 ./tag-latest

# building latest tag (for arm64v8 arch)
docker build --tag local/centos-8:latest --file ./tag-latest/Dockerfile.arm64v8 ./tag-latest

# building latest tag (for ppc64le arch)
docker build --tag local/centos-8:latest --file ./tag-latest/Dockerfile.ppc64le ./tag-latest

# building init tag
# NOTE: you need to edit file './tag-init/Dockerfile' and change 'FROM docker.io/adevur/centos-8:latest' to 'FROM local/centos-8:latest'
docker build --tag local/centos-8:init ./tag-init

# building systemd tag
# NOTE: you need to edit file './tag-systemd/Dockerfile' and change 'FROM docker.io/adevur/centos-8:latest' to 'FROM local/centos-8:latest'
docker build --tag local/centos-8:systemd ./tag-systemd

Create a tarball using a kickstart script

In order to generate a centos-8.tar.xz tarball, we need a CentOS 7.x/8.x machine. In this tutorial, we're gonna use a container with adevur/centos-8:latest (that provides a CentOS 8 environment), so that we can generate the tarball on any Linux machine.

• First, let's create a directory on our system, where we'll put all the files we need (including the newly-generated tarball):

  mkdir /tarball-builder

• Let's put the kickstart script into /tarball-builder:

  # in this tutorial, we're gonna use the already-written kickstart script found on this GitHub,
  #   but you can also edit or rewrite this kickstart if you want to
  curl -sL https://raw.githubusercontent.com/adevur/docker-centos-8/master/tag-latest/centos-8-adevur0-amd64.ks > /tarball-builder/centos-8.ks

• Let's set up our environment with CentOS 8 installed in it:

  # NOTE: you can also set up the container with CentOS 7 installed, and it should work the same, but it's not been tested
  docker run -v /tarball-builder:/tarball-builder --privileged --name tarball-builder --rm -it adevur/centos-8:latest /bin/bash

• Now that we're inside the container, let's install the software needed to generate the tarball (i.e. packages lorax and anaconda-tui):

  yum clean all && yum install -y lorax anaconda-tui && yum clean all

• We can now generate the tarball and save it to /tarball-builder:

  cd /tarball-builder
  
  livemedia-creator --no-virt --make-tar --ks centos-8.ks --image-name=centos-8.tar.xz --project "CentOS 8 Docker" --releasever "8"
  
  mv /var/tmp/centos-8.tar.xz /tarball-builder/centos-8.tar.xz
  
  exit

• Now we can exit from the container: our tarball has been generated and is located at path /tarball-builder/centos-8.tar.xz on our computer. You can use this tarball to build tag latest of adevur/centos-8 Docker image.