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In every docker tutorial, one of the main advantages of the docker is that docker container use host OS. But if that is true, I don't understand why I need to include OS in the image. For example here is image of centOS. I understand that if I want to run centOS in container I must pull this image but where then host OS come? It would be best if someone can point me to some link to read about that because I cannot find appropriate one.

Spasoje Petronijević
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2 Answers2

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What Docker uses of the host is actually only the OS's kernel.

What you include in the Docker container is not the actual OS (i.e., the kernel), but rather all the files that make up a specific distribution, such as Ubuntu or Fedora, or whatever…

This is also the reason why you can't run Linux containers on Windows and vice-versa (without a VM), because Linux software of course doesn't work with the Windows kernel, and Windows software doesn't work with the Linux kernel.

So, all Docker containers running on a given host share the host OS's kernel.

Golo Roden
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It actually shares the kernel & required libraries to boot the image from host OS. That's why those images are really small & not like traditional ISO files. It primarily utilizes union file system, cgroups and namespaces to manage the images and containers.

You can give a quick read to below -
https://kjanshair.github.io/2017/07/04/Docker-Containers-vs-System-Processes/ How is Docker different from a normal virtual machine?

vivekyad4v
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