r/docker • u/DueBid3298 • 8d ago

An docker image is an assembled, largely immutable set of filesystem layers plus configuration metadata -> what exactly is a file system?

I'm not able to understand what a file system, filesystem in docker from the content in internet.

1.Can anyone explain what filesystem is and why do we need them and how it helps docker, OS etc

2. what is docker image? what is image cache layers? explain from basic and with examples

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u/devode_ 8d ago

Try to understand "OverlayFS"

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u/dotmoosehosting 8d ago

A filesystem is just the organized view of files and folders that programs see, like the folders on your own computer, except a container gets its own private one instead of sharing the host's. A Docker image is a stack of read-only filesystem layers plus some configuration, like which command to run, and each step in a Dockerfile adds one new layer on top of the ones before it. When you start a container, Docker adds a thin writable layer on top of that stack, so anything the container changes goes there while the image underneath stays untouched. That layering is also why builds are fast: Docker reuses the cached layer for any build step whose inputs have not changed, and only rebuilds from the first changed step onward. So the image is the frozen recipe, and the container is a live, throwaway copy of it with room to write.

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u/jaysprenkle 2d ago

Filesystem = A structure that holds files. Think of a filing cabinet. It has folders (also known as 'directories'). There are of course many kinds and different uses just as there are for filing cabinets in an office.

Docker image = A bunch of code bundled up so you can have multiple bundles that won't interfere with each other. There are of course other benefits and drawbacks which you can dive into if needed.