Container filesystem is ephemeral in Docker - Step-by-Step Execution

Process Flow - Container filesystem is ephemeral

Start Container

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Container Filesystem Created

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Write Files Inside Container

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Stop & Remove Container

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Container Filesystem Deleted

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Start New Container

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Fresh Filesystem, No Previous Data

This flow shows how a container's filesystem is created fresh at start, changes are temporary, and are lost when the container is stopped and removed.

Execution Sample

Docker

docker run -d --name test1 alpine sh -c "echo hello > /file.txt && sleep 3600"
docker stop test1
docker rm test1
docker run --name test2 alpine cat /file.txt

This sequence creates a container that writes a file, stops and removes it, then starts a new container trying to read that file.

Process Table

Step	Command	Action	Filesystem State	Output
1	docker run -d --name test1 alpine sh -c "echo hello > /file.txt && sleep 3600"	Start container and write file	File /file.txt created with content 'hello'
2	docker stop test1	Stop container	Filesystem still exists but container stopped
3	docker rm test1	Remove container and its filesystem	Filesystem deleted
4	docker run --name test2 alpine cat /file.txt	Start new container and try to read file	Fresh filesystem, no /file.txt	cat: /file.txt: No such file or directory

💡 New container has a fresh filesystem; previous container's files are lost because container filesystem is ephemeral.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4
Filesystem /file.txt	absent	present with 'hello'	present with 'hello'	deleted	absent

Key Moments - 2 Insights

Why can't the new container read the file created by the old container?

Because each container has its own temporary filesystem that is deleted when the container is removed, as shown in step 3 where the filesystem is deleted.

Does stopping a container delete its filesystem?

No, stopping only pauses the container but the filesystem remains until the container is removed, as seen between steps 2 and 3.

Visual Quiz - 3 Questions

Look at the execution table, what is the output when the new container tries to read /file.txt?

A "hello"

B Empty output

C "cat: /file.txt: No such file or directory"

D Error: container not found

💡 Hint

Check step 4 in the execution table under Output column.

At which step is the container filesystem deleted?

A Step 3

B Step 2

C Step 1

D Step 4

💡 Hint

Look at the Action and Filesystem State columns in the execution table.

If we did not remove the first container, what would happen when starting the second container?

A The second container would see the file /file.txt

B The second container would still have a fresh filesystem

C Docker would throw an error about container name conflict

D The file would be empty

💡 Hint

Container names are test1 and test2 (different), so no name conflict. Each container has its own independent fresh filesystem.

Concept Snapshot

Container filesystem is temporary.
Files created inside a container exist only while it runs.
Stopping a container keeps filesystem; removing deletes it.
New containers start with a clean filesystem.
Use volumes to keep data persistent outside containers.

Full Transcript

When you start a Docker container, it creates a fresh filesystem. Any files you create inside exist only while the container runs. If you stop the container, the filesystem stays but the container is paused. When you remove the container, its filesystem is deleted. Starting a new container creates a new fresh filesystem without any files from the old container. This means container filesystems are ephemeral, or temporary. To keep data beyond container life, you use volumes. This example showed creating a file in one container, stopping and removing it, then starting a new container that could not see the old file.