Docker Where Are Images Stored

Docker installed on windows with docker toolbox (using virtual box in place of hyper-v) one VM is created on at C:UsersYOURUSERNAME.dockermachinemachines with name default so you can find all VM files in default folder. You can connect this vm using. The heaviest contents are usually images. If you use the default storage driver overlay2, then your Docker images are stored in /var/lib/docker/overlay2. There, you can find different files that represent read-only layers of a Docker image and a layer on top of it that contains your changes. Location of Dockers images in all Operating Systems The location of the images vary depending on the driver Docker is using for storage. Actually, Docker images are. Do Not Confuse: Docker images themselves are never 'started' and never 'running'. The docker run command takes the Docker image as a template and produces a container from it. Images are created from a Dockerfile with the docker build command. Images are stored in a Docker registry, such as Docker Hub and can be downloaded with the.

• Docker Where Are Images Stored As A
• Docker Where Are Images Stored Different
• Docker Desktop Where Are Images Stored
• Where Are Docker Images Stored Windows 10

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To use storage drivers effectively, it's important to know how Docker builds andstores images, and how these images are used by containers. You can use thisinformation to make informed choices about the best way to persist data fromyour applications and avoid performance problems along the way.

Storage drivers allow you to create data in the writable layer of your container.The files won't be persisted after the container is deleted, and both read andwrite speeds are lower than native file system performance.

Note: Operations that are known to be problematic include write-intensive database storage,particularly when pre-existing data exists in the read-only layer. More details are provided in this document.

Learn how to use volumes to persist data and improve performance.

Images and layers

A Docker image is built up from a series of layers. Each layer represents aninstruction in the image's Dockerfile. Each layer except the very last one isread-only. Consider the following Dockerfile:

This Dockerfile contains four commands, each of which creates a layer. TheFROM statement starts out by creating a layer from the ubuntu:18.04 image.The COPY command adds some files from your Docker client's current directory.The RUN command builds your application using the make Ee help and support. command. Finally,the last layer specifies what command to run within the container.

Each layer is only a set of differences from the layer before it. The layers arestacked on top of each other. When you create a new container, you add a newwritable layer on top of the underlying layers. This layer is often called the'container layer'. All changes made to the running container, such as writingnew files, modifying existing files, and deleting files, are written to this thinwritable container layer. The diagram below shows a container based on the Ubuntu15.04 image.

A storage driver handles the details about the way these layers interact witheach other. Different storage drivers are available, which have advantagesand disadvantages in different situations.

Container and layers

The major difference between a container and an image is the top writable layer.All writes to the container that add new or modify existing data are stored inthis writable layer. When the container is deleted, the writable layer is alsodeleted. The underlying image remains unchanged.

Because each container has its own writable container layer, and all changes arestored in this container layer, multiple containers can share access to the sameunderlying image and yet have their own data state. The diagram below showsmultiple containers sharing the same Ubuntu 15.04 image.

Note: If you need multiple images to have shared access to the exactsame data, store this data in a Docker volume and mount it into yourcontainers.

Docker uses storage drivers to manage the contents of the image layers and thewritable container layer. Each storage driver handles the implementationdifferently, but all drivers use stackable image layers and the copy-on-write(CoW) strategy.

Container size on disk

To view the approximate size of a running container, you can use the docker ps -scommand. Two different columns relate to size.

• size: the amount of data (on disk) that is used for the writable layer ofeach container.

• virtual size: the amount of data used for the read-only image dataused by the container plus the container's writable layer size.Multiple containers may share some or all read-onlyimage data. Two containers started from the same image share 100% of theread-only data, while two containers with different images which have layersin common share those common layers. Therefore, you can't just total thevirtual sizes. This over-estimates the total disk usage by a potentiallynon-trivial amount.

The total disk space used by all of the running containers on disk is somecombination of each container's size and the virtual size values. Ifmultiple containers started from the same exact image, the total size on disk forthese containers would be SUM (size of containers) plus one image size(virtual size- size).

This also does not count the following additional ways a container can take updisk space:

• Disk space used for log files if you use the json-file logging driver. Thiscan be non-trivial if your container generates a large amount of logging dataand log rotation is not configured.
• Volumes and bind mounts used by the container.
• Disk space used for the container's configuration files, which are typicallysmall.
• Memory written to disk (if swapping is enabled).
• Checkpoints, if you're using the experimental checkpoint/restore feature.

The copy-on-write (CoW) strategy

Copy-on-write is a strategy of sharing and copying files for maximum efficiency.If a file or directory exists in a lower layer within the image, and anotherlayer (including the writable layer) needs read access to it, it just uses theexisting file. The first time another layer needs to modify the file (whenbuilding the image or running the container), the file is copied into that layerand modified. This minimizes I/O and the size of each of the subsequent layers.These advantages are explained in more depth below.

Sharing promotes smaller images

When you use docker pull to pull down an image from a repository, or when youcreate a container from an image that does not yet exist locally, each layer ispulled down separately, and stored in Docker's local storage area, which isusually /var/lib/docker/ on Linux hosts. You can see these layers being pulledin this example:

Each of these layers is stored in its own directory inside the Docker host'slocal storage area. To examine the layers on the filesystem, list the contentsof /var/lib/docker/. This example uses the overlay2 storage driver:

The directory names do not correspond to the layer IDs (this has been true sinceDocker 1.10).

Now imagine that you have two different Dockerfiles. You use the first one tocreate an image called acme/my-base-image:1.0.

Docker Where Are Images Stored As A

The second one is based on acme/my-base-image:1.0, but has some additionallayers:

The second image contains all the layers from the first image, plus a new layerwith the CMD instruction, and a read-write container layer. Docker alreadyhas all the layers from the first image, so it does not need to pull them again.The two images share any layers they have in common.

Docker Where Are Images Stored Different

If you build images from the two Dockerfiles, you can use docker image ls anddocker history commands to verify that the cryptographic IDs of the sharedlayers are the same.

1. Make a new directory cow-test/ and change into it.

2. Within cow-test/, create a new file called hello.sh with the following contents:

   Save the file, and make it executable:

3. Copy the contents of the first Dockerfile above into a new file calledDockerfile.base.

4. Copy the contents of the second Dockerfile above into a new file calledDockerfile.

5. Within the cow-test/ directory, build the first image. Don't forget toinclude the final . in the command. That sets the PATH, which tellsDocker where to look for any files that need to be added to the image.

6. Build the second image.

7. Check out the sizes of the images:

8. Check out the layers that comprise each image:

   Notice that all the layers are identical except the top layer of the secondimage. All the other layers are shared between the two images, and are onlystored once in /var/lib/docker/. The new layer actually doesn't take anyroom at all, because it is not changing any files, but only running a command.

   Note: The lines in the docker history output indicatethat those layers were built on another system and are not availablelocally. I want blacks login. This can be ignored.

Copying makes containers efficient

When you start a container, a thin writable container layer is added on top ofthe other layers. Any changes the container makes to the filesystem are storedhere. Any files the container does not change do not get copied to this writablelayer. This means that the writable layer is as small as possible.

When an existing file in a container is modified, the storage driver performs acopy-on-write operation. The specifics steps involved depend on the specificstorage driver. For the aufs, overlay, and overlay2 drivers, the copy-on-write operation follows this rough sequence:

• Search through the image layers for the file to update. The process startsat the newest layer and works down to the base layer one layer at a time.When results are found, they are added to a cache to speed future operations.

• Perform a copy_up operation on the first copy of the file that is found, tocopy the file to the container's writable layer.

• Any modifications are made to this copy of the file, and the container cannotsee the read-only copy of the file that exists in the lower layer.

Btrfs, ZFS, and other drivers handle the copy-on-write differently. You canread more about the methods of these drivers later in their detaileddescriptions.

Containers that write a lot of data consume more space than containersthat do not. This is because most write operations consume new space in thecontainer's thin writable top layer.

Note: for write-heavy applications, you should not store the data inthe container. Instead, use Docker volumes, which are independent of therunning container and are designed to be efficient for I/O. In addition,volumes can be shared among containers and do not increase the size of yourcontainer's writable layer.

A copy_up operation can incur a noticeable performance overhead. This overheadis different depending on which storage driver is in use. Large files,lots of layers, and deep directory trees can make the impact more noticeable.This is mitigated by the fact that each copy_up operation only occurs the firsttime a given file is modified.

To verify the way that copy-on-write works, the following procedures spins up 5containers based on the acme/my-final-image:1.0 image we built earlier andexamines how much room they take up.

Note: This procedure doesn't work on Docker Desktop for Mac or Docker Desktop for Windows.

1. From a terminal on your Docker host, run the following docker run commands.The strings at the end are the IDs of each container.

2. Run the docker ps command to verify the 5 containers are running.

3. List the contents of the local storage area.

4. Now check out their sizes:

   Each of these containers only takes up 32k of space on the filesystem.

Not only does copy-on-write save space, but it also reduces start-up time.When you start a container (or multiple containers from the same image), Dockeronly needs to create the thin writable container layer.

If Docker had to make an entire copy of the underlying image stack each time itstarted a new container, container start times and disk space used would besignificantly increased. This would be similar to the way that virtual machineswork, with one or more virtual disks per virtual machine.

Related information

Just a few weeks until the 2021 JavaScript Full-Stack Bootcamp opens.
Signup to the waiting list!

A Docker image is a template for a container.

Everything starts from a Docker image.

When you tell Docker to create a container from an image using docker run, it will perform its magic (create the file system, initialize the dependencies, and more) and then the container will be created.

Images are built from a Dockerfile using the docker build command, and they can be stored locally, or published in a Docker registry like Docker Hub, where you can store public and private images.

If you visit https://hub.docker.com/ you will see a lot of images you can freely use without having to create your own images.

Often times those images are official and made by the development teams behind a specific technology.

For example this is the official Node.js Docker Image: https://registry.hub.docker.com/_/node.

Docker Desktop Where Are Images Stored

We'll talk more about how to use images and containers soon.

The 2021 JavaScript Full-Stack Bootcamp will start at the end of March 2021. Don't miss this opportunity, signup to the waiting list!

More docker tutorials:

Where Are Docker Images Stored Windows 10

Learn how to use volumes to persist data and improve performance.

Images and layers

A Docker image is built up from a series of layers. Each layer represents aninstruction in the image's Dockerfile. Each layer except the very last one isread-only. Consider the following Dockerfile:

This Dockerfile contains four commands, each of which creates a layer. TheFROM statement starts out by creating a layer from the ubuntu:18.04 image.The COPY command adds some files from your Docker client's current directory.The RUN command builds your application using the make Ee help and support. command. Finally,the last layer specifies what command to run within the container.

Each layer is only a set of differences from the layer before it. The layers arestacked on top of each other. When you create a new container, you add a newwritable layer on top of the underlying layers. This layer is often called the'container layer'. All changes made to the running container, such as writingnew files, modifying existing files, and deleting files, are written to this thinwritable container layer. The diagram below shows a container based on the Ubuntu15.04 image.

A storage driver handles the details about the way these layers interact witheach other. Different storage drivers are available, which have advantagesand disadvantages in different situations.

Container and layers

The major difference between a container and an image is the top writable layer.All writes to the container that add new or modify existing data are stored inthis writable layer. When the container is deleted, the writable layer is alsodeleted. The underlying image remains unchanged.

Because each container has its own writable container layer, and all changes arestored in this container layer, multiple containers can share access to the sameunderlying image and yet have their own data state. The diagram below showsmultiple containers sharing the same Ubuntu 15.04 image.

Note: If you need multiple images to have shared access to the exactsame data, store this data in a Docker volume and mount it into yourcontainers.

Docker uses storage drivers to manage the contents of the image layers and thewritable container layer. Each storage driver handles the implementationdifferently, but all drivers use stackable image layers and the copy-on-write(CoW) strategy.

Container size on disk

To view the approximate size of a running container, you can use the docker ps -scommand. Two different columns relate to size.

• size: the amount of data (on disk) that is used for the writable layer ofeach container.

• virtual size: the amount of data used for the read-only image dataused by the container plus the container's writable layer size.Multiple containers may share some or all read-onlyimage data. Two containers started from the same image share 100% of theread-only data, while two containers with different images which have layersin common share those common layers. Therefore, you can't just total thevirtual sizes. This over-estimates the total disk usage by a potentiallynon-trivial amount.

The total disk space used by all of the running containers on disk is somecombination of each container's size and the virtual size values. Ifmultiple containers started from the same exact image, the total size on disk forthese containers would be SUM (size of containers) plus one image size(virtual size- size).

This also does not count the following additional ways a container can take updisk space:

• Disk space used for log files if you use the json-file logging driver. Thiscan be non-trivial if your container generates a large amount of logging dataand log rotation is not configured.
• Volumes and bind mounts used by the container.
• Disk space used for the container's configuration files, which are typicallysmall.
• Memory written to disk (if swapping is enabled).
• Checkpoints, if you're using the experimental checkpoint/restore feature.

The copy-on-write (CoW) strategy

Copy-on-write is a strategy of sharing and copying files for maximum efficiency.If a file or directory exists in a lower layer within the image, and anotherlayer (including the writable layer) needs read access to it, it just uses theexisting file. The first time another layer needs to modify the file (whenbuilding the image or running the container), the file is copied into that layerand modified. This minimizes I/O and the size of each of the subsequent layers.These advantages are explained in more depth below.

Sharing promotes smaller images

When you use docker pull to pull down an image from a repository, or when youcreate a container from an image that does not yet exist locally, each layer ispulled down separately, and stored in Docker's local storage area, which isusually /var/lib/docker/ on Linux hosts. You can see these layers being pulledin this example:

Each of these layers is stored in its own directory inside the Docker host'slocal storage area. To examine the layers on the filesystem, list the contentsof /var/lib/docker/. This example uses the overlay2 storage driver:

The directory names do not correspond to the layer IDs (this has been true sinceDocker 1.10).

Now imagine that you have two different Dockerfiles. You use the first one tocreate an image called acme/my-base-image:1.0.

Docker Where Are Images Stored As A

The second one is based on acme/my-base-image:1.0, but has some additionallayers:

The second image contains all the layers from the first image, plus a new layerwith the CMD instruction, and a read-write container layer. Docker alreadyhas all the layers from the first image, so it does not need to pull them again.The two images share any layers they have in common.

Docker Where Are Images Stored Different

If you build images from the two Dockerfiles, you can use docker image ls anddocker history commands to verify that the cryptographic IDs of the sharedlayers are the same.

1. Make a new directory cow-test/ and change into it.

2. Within cow-test/, create a new file called hello.sh with the following contents:

   Save the file, and make it executable:

3. Copy the contents of the first Dockerfile above into a new file calledDockerfile.base.

4. Copy the contents of the second Dockerfile above into a new file calledDockerfile.

5. Within the cow-test/ directory, build the first image. Don't forget toinclude the final . in the command. That sets the PATH, which tellsDocker where to look for any files that need to be added to the image.

6. Build the second image.

7. Check out the sizes of the images:

8. Check out the layers that comprise each image:

   Notice that all the layers are identical except the top layer of the secondimage. All the other layers are shared between the two images, and are onlystored once in /var/lib/docker/. The new layer actually doesn't take anyroom at all, because it is not changing any files, but only running a command.

   Note: The lines in the docker history output indicatethat those layers were built on another system and are not availablelocally. I want blacks login. This can be ignored.

Copying makes containers efficient

When you start a container, a thin writable container layer is added on top ofthe other layers. Any changes the container makes to the filesystem are storedhere. Any files the container does not change do not get copied to this writablelayer. This means that the writable layer is as small as possible.

When an existing file in a container is modified, the storage driver performs acopy-on-write operation. The specifics steps involved depend on the specificstorage driver. For the aufs, overlay, and overlay2 drivers, the copy-on-write operation follows this rough sequence:

• Search through the image layers for the file to update. The process startsat the newest layer and works down to the base layer one layer at a time.When results are found, they are added to a cache to speed future operations.

• Perform a copy_up operation on the first copy of the file that is found, tocopy the file to the container's writable layer.

• Any modifications are made to this copy of the file, and the container cannotsee the read-only copy of the file that exists in the lower layer.

Btrfs, ZFS, and other drivers handle the copy-on-write differently. You canread more about the methods of these drivers later in their detaileddescriptions.

Containers that write a lot of data consume more space than containersthat do not. This is because most write operations consume new space in thecontainer's thin writable top layer.

Note: for write-heavy applications, you should not store the data inthe container. Instead, use Docker volumes, which are independent of therunning container and are designed to be efficient for I/O. In addition,volumes can be shared among containers and do not increase the size of yourcontainer's writable layer.

A copy_up operation can incur a noticeable performance overhead. This overheadis different depending on which storage driver is in use. Large files,lots of layers, and deep directory trees can make the impact more noticeable.This is mitigated by the fact that each copy_up operation only occurs the firsttime a given file is modified.

To verify the way that copy-on-write works, the following procedures spins up 5containers based on the acme/my-final-image:1.0 image we built earlier andexamines how much room they take up.

Note: This procedure doesn't work on Docker Desktop for Mac or Docker Desktop for Windows.

1. From a terminal on your Docker host, run the following docker run commands.The strings at the end are the IDs of each container.

2. Run the docker ps command to verify the 5 containers are running.

3. List the contents of the local storage area.

4. Now check out their sizes:

   Each of these containers only takes up 32k of space on the filesystem.

Not only does copy-on-write save space, but it also reduces start-up time.When you start a container (or multiple containers from the same image), Dockeronly needs to create the thin writable container layer.

If Docker had to make an entire copy of the underlying image stack each time itstarted a new container, container start times and disk space used would besignificantly increased. This would be similar to the way that virtual machineswork, with one or more virtual disks per virtual machine.

Related information

Just a few weeks until the 2021 JavaScript Full-Stack Bootcamp opens.
Signup to the waiting list!

A Docker image is a template for a container.

Everything starts from a Docker image.

When you tell Docker to create a container from an image using docker run, it will perform its magic (create the file system, initialize the dependencies, and more) and then the container will be created.

Images are built from a Dockerfile using the docker build command, and they can be stored locally, or published in a Docker registry like Docker Hub, where you can store public and private images.

If you visit https://hub.docker.com/ you will see a lot of images you can freely use without having to create your own images.

Often times those images are official and made by the development teams behind a specific technology.

For example this is the official Node.js Docker Image: https://registry.hub.docker.com/_/node.

Docker Desktop Where Are Images Stored

We'll talk more about how to use images and containers soon.

The 2021 JavaScript Full-Stack Bootcamp will start at the end of March 2021. Don't miss this opportunity, signup to the waiting list!

More docker tutorials:

Where Are Docker Images Stored Windows 10