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containers-storage - Manage layer/image/container storage
containers-storage [subcommand] [--help]
The containers-storage command is a front-end for the containers/storage library. While it can be used to manage storage for filesystem layers, images, and containers directly, its main use cases are centered around troubleshooting and querying the state of storage which is being managed by other processes.
Notionally, a complete filesystem layer is composed of a container filesystem and some bookkeeping information. Other layers, children of that layer, default to sharing its contents, but any changes made to the contents of the children are not reflected in the parent. This arrangement is intended to save disk space: by storing the child layer only as a set of changes relative to its parent, the parent's contents should not need to be duplicated for each of the parent's children. Of course, each child can have its own children. The contents of parent layers should not be modified.
An image is a reference to a particular layer, along with some bookkeeping information. Presumably, the image points to a layer which has been modified, possibly in multiple steps, from some general-purpose parent, so that it is suitable for running an intended application. Multiple images can reference a single layer, while differing only in the additional bookkeeping information that they carry. The contents of images should be considered read-only.
A container is essentially a layer which is a child of a layer which is referred to by an image (put another way, a container is instantiated from an image), along with some bookkeeping information. They do not have children and their layers can not be directly referred to by images. This ensures that changes to the contents of a container's layer do not affect other images or layers, so they are considered writeable.
All of layers, images, and containers can have metadata which containers-storage manages attached to them. Generally this metadata is not expected to be large, as it is cached in memory.
Images and containers can also have arbitrarily-named data items attached to them. Generally, this data can be larger than metadata, and is not kept in memory unless it is being retrieved or written.
It is expected that signatures which can be used to verify an image's contents will be stored as data items for that image, along with any template configuration data which is recommended for use in containers which derive from the image. It is also expected that a container's run-time configuration will be stored as data items.
The containers-storage command's features are broken down
into several subcommands:
containers-storage add-names(1) Add layer, image, or container name or
names
containers-storage applydiff(1) Apply a diff to a layer
containers-storage changes(1) Compare two layers
containers-storage container(1) Examine a container
containers-storage containers(1) List containers
containers-storage create-container(1) Create a new container from an image
containers-storage create-image(1) Create a new image using layers
containers-storage create-layer(1) Create a new layer
containers-storage delete(1) Delete a layer or image or container, with no safety checks
containers-storage delete-container(1) Delete a container, with safety checks
containers-storage delete-image(1) Delete an image, with safety checks
containers-storage delete-layer(1) Delete a layer, with safety checks
containers-storage diff(1) Compare two layers
containers-storage diffsize(1) Compare two layers
containers-storage exists(1) Check if a layer or image or container exists
containers-storage get-container-data(1) Get data that is attached to a container
containers-storage get-image-data(1) Get data that is attached to an image
containers-storage image(1) Examine an image
containers-storage images(1) List images
containers-storage layers(1) List layers
containers-storage list-container-data(1) List data items that are attached to a container
containers-storage list-image-data(1) List data items that are attached to an image
containers-storage metadata(1) Retrieve layer, image, or container metadata
containers-storage mount(1) Mount a layer or container
containers-storage mounted(1) Check if a file system is mounted
containers-storage set-container-data(1) Set data that is attached to a container
containers-storage set-image-data(1) Set data that is attached to an image
containers-storage set-metadata(1) Set layer, image, or container metadata
containers-storage set-names(1) Set layer, image, or container name or names
containers-storage shutdown(1) Shut down graph driver
containers-storage status(1) Check on graph driver status
containers-storage unmount(1) Unmount a layer or container
containers-storage version(1) Return containers-storage version information
containers-storage wipe(1) Wipe all layers, images, and containers
--help
Print the list of available sub-commands. When a sub-command is specified, provide information about that command.
--debug, -D
Increases the amount of debugging information which is printed.
--graph, -g=/var/lib/containers/storage
Overrides the root of the storage tree, used for storing layer contents and information about layers, images, and containers.
--run, -R=/run/containers/storage
Overrides the root of the runtime state tree, currently used mainly for noting the location where a given layer is mounted (see containers-storage mount) so that it can be unmounted by path name as an alternative to unmounting by ID or name.
--storage-driver, -s
Specifies which storage driver to use. If not set, but $STORAGE_DRIVER is set in the environment, its value is used. If the storage tree has previously been initialized, neither needs to be provided. If the tree has not previously been initialized and neither is set, a hard-coded default is selected.
--storage-opt=[]
Set options which will be passed to the storage driver. If not set, but $STORAGE_OPTS is set in the environment, its value is treated as a comma-separated list and used instead. If the storage tree has previously been initialized, these need not be provided.
containers-storage layers -t
This is still a work in progress, so some functionality may not yet be implemented, and some will be removed if it is found to be unnecessary. That said, if anything isn't working correctly, please report it to the project's issue tracker ⟨https://github.com/containers/storage/issues⟩.
The Containers Storage project is committed to inclusivity, a core value of open source. The master and slave mount propagation terminology is used in this repository. This language is problematic and divisive, and should be changed. However, these terms are currently used within the Linux kernel and must be used as-is at this time. When the kernel maintainers rectify this usage, Containers Storage will follow suit immediately.