Where are Docker images stored?

The storage location of Docker images and containers depends on the operating system. The command docker info provides information about your Docker configuration, including the Storage Driver and the Docker Root Dir.

On Ubuntu, Docker stores images and containers files under /var/lib/docker:

sudo ls /var/lib/docker/ -latr
total 60
drwxr-xr-x 40 root root  4096 May 27 13:27 ..
drwx------  3 root root  4096 May 27 13:27 image
drwx------  2 root root  4096 May 27 13:27 trust
drwxr-x---  3 root root  4096 May 27 13:27 network
drwx------  2 root root  4096 May 27 13:27 swarm
drwx--x--x  4 root root  4096 May 27 13:27 buildkit
drwx------  2 root root  4096 May 27 13:27 runtimes
drwx--x--x 13 root root  4096 May 27 13:27 .
drwx-----x  3 root root  4096 May 27 18:23 volumes
drwx------  4 root root  4096 Jun  2 15:50 plugins
drwx------  2 root root  4096 Jun  3 10:58 tmp
drwx-----x  6 root root 12288 Jun  3 10:58 overlay2
drwx-----x  3 root root  4096 Jun  3 10:58 containers

Docker images are stored in /var/lib/docker/overlay2.

Let's explore the content of our image hello-world:

Info

The command docker inspect returns low-level information on Docker objects (images, containers, networks, etc.).

More info in the Docker official doc.

docker image inspect hello-world

[
    {
        "Id": "sha256:d1165f2212346b2bab48cb01c1e39ee8ad1be46b87873d9ca7a4e434980a7726",
        "RepoTags": [
            "hello-world:latest"
        ],
....
        "GraphDriver": {
            "Data": {
                "MergedDir": "/var/lib/docker/overlay2/f9457322a6bf658b38d3faf3bdd607f6873b89e3be2e9de222c9eb81a069f29d/merged",
                "UpperDir": "/var/lib/docker/overlay2/f9457322a6bf658b38d3faf3bdd607f6873b89e3be2e9de222c9eb81a069f29d/diff",
                "WorkDir": "/var/lib/docker/overlay2/f9457322a6bf658b38d3faf3bdd607f6873b89e3be2e9de222c9eb81a069f29d/work"
            },
            "Name": "overlay2"
        },
....

The GraphDriver.Data dictionary contains information about the layers of the image.

In general, the LowerDir contains the read-only layers of an image. The read-write layer that represents changes are part of the UpperDir.

The hello-world image is built starting from the base image scratch that is an explicitly empty image.

The hello-world image therefore contains just one layer that adds the hello executable (statically linked) to the base empty image.

Look at the content of the UpperDir:

sudo ls -latr /var/lib/docker/overlay2/f9457322a6bf658b38d3faf3bdd607f6873b89e3be2e9de222c9eb81a069f29d/diff
total 24
-rwxrwxr-x 1 root root 13336 Mar  5 23:25 hello
drwxr-xr-x 2 root root  4096 Jun  3 14:39 .
drwx-----x 3 root root  4096 Jun  3 14:39 ..

Another interesting command is docker history that shows the hystory of an image. Try it!

docker history hello-world

Output:

IMAGE          CREATED        CREATED BY                                      SIZE      COMMENT
d1165f221234   2 months ago   /bin/sh -c #(nop)  CMD ["/hello"]               0B
<missing>      2 months ago   /bin/sh -c #(nop) COPY file:7bf12aab75c3867a…   13.3kB

Again, you can see here that the image has only one layer (0B lines are neglected).