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- So in this video,
I will tell you how containers

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and Linux are closely related.

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From a Linux point of view,

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a container is an isolated process

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that runs with restricted resources.

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The Linux kernel provides
namespaces and cgroups

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as a supporting features to do so.

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The namespace is for the isolation.

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The cgroup is for resource allocation.

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Namespaces have evolved from chroot,

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a solution that has been used for decades

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to run a process with a
"fake root" directory.

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We have seen chroot in the
lesson about troubleshooting

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the boot proceeder.

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To learn a successful chroot process,

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all dependencies that are
required by the process

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that is running in the
chrooted environment

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are required in the chrooted directory.

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So if you want to learn your web server

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as a chroot process,
all of the dependencies

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need to be present for this web server

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in this chroot directory.

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From chroot to container is
actually a very small step.

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Initially, the required
dependencies were copied manually

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into the chrooted directory.

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That's before the days that

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we were talking about containers.

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Nowadays we have container images.

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The container image is really a tarball

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that comes with the container.

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It's an archive of files

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provided in a standardized format.

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The standardization for
these images is provided

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by the Open Containers Initiative, or OCI,

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which is a foundation
within LinuxFoundation.

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And OCI images are based on Docker images.

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So let's talk a bit about Docker.

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Before Docker, LXC, which
is Linux Native Containers,

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was a common way to learn containers,

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and LXC comes very close
to learning scripts

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where Tarballs are used
in chrooted directories.

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That was foundation, the
origin of the container.

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Now in 2013, Docker started
the Container Revolution.

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Initially Docker was based on LXC,

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but Docker introduced
the Docker image format

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as well as the Docker registry

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which is also known as Docker Hub.

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Docker Hub is a public platform

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where anyone can get and
post container images.

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It's a little bit like GitHub,

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but specifically for container images

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and there's more than 10
million container images

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available on Docker Hub right now.

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The Docker image format
introduced a solution

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to build container images in a smart way,

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using common images as parent images

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to which only modifications
needed to be added.

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What does that mean?

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Well, if you want to run
a database application

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then you can focus on your own application

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and build a container image in which

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a standard database image is used,

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so you don't have to build
everything from scratch.

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You can use already existing components

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and fetch these from the image registry,

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such as Docker Hub, and that really made

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working with containers a lot easier.

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At its launch, Docker
was mainly open source.

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Over the years, the company behind Docker

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has moved components to
a closed source model.

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And that created challenges for companies

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that are using Docker
containers, including a Red Hat.

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Because of Red Hat,

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which after all is the
biggest Linux distribution,

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because Red Hat needed a
pure open source solution

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instead of a semi-proprietary solution,

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they introduced podman

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with the release of RHEL 8 in 2018.

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Podman of course is an open source project

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that has been adopted by Red Hat.

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As podman and Docker
are fully OCI compliant,

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replacing Docker with
podman is effortless.

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You just need to type the
command podman instead of Docker.

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And if you don't want to do that,

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you just type alias docker is podman.

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Currently, podman is widely
adopted and available

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in all main Linux distributions.

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Now working with podman
has a couple of benefits.

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First, podman installation is very easy.

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Just use your local package
manager to install it.

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So sudo apt install podman
and you're ready to go.

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Podman requires no daemons
or elevated privileges.

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And podman allows for rootless containers.

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In fact, rootless
containers are the default

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and that means that management
of restricted user entities

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inside containers is much
easier and much more secure.

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Podman is also a full
open source solution.

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And last, there was one thing very smart

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that the podman developers have done,

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and that is that they
created a command line

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that is compatible to Docker.

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So you just replaced the
Docker command with podman

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and you are ready to go

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and that makes a transition very easy.

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In the next video

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you'll learn more about container images.