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8 KiB
Markdown
---
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description: "How to manage image and container filesystems with external plugins"
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keywords: "Examples, Usage, storage, image, docker, data, graph, plugin, api"
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advisory: experimental
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---
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# Graphdriver plugins
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## Changelog
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### 1.13.0
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- Support v2 plugins
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# Docker graph driver plugins
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Docker graph driver plugins enable admins to use an external/out-of-process
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graph driver for use with Docker engine. This is an alternative to using the
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built-in storage drivers, such as aufs/overlay/devicemapper/btrfs.
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You need to install and enable the plugin and then restart the Docker daemon
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before using the plugin. See the following example for the correct ordering
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of steps.
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```
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$ docker plugin install cpuguy83/docker-overlay2-graphdriver-plugin # this command also enables the driver
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<output suppressed>
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$ pkill dockerd
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$ dockerd --experimental -s cpuguy83/docker-overlay2-graphdriver-plugin
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```
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# Write a graph driver plugin
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See the [plugin documentation](https://docs.docker.com/engine/extend/) for detailed information
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on the underlying plugin protocol.
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## Graph Driver plugin protocol
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If a plugin registers itself as a `GraphDriver` when activated, then it is
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expected to provide the rootfs for containers as well as image layer storage.
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### /GraphDriver.Init
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**Request**:
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```json
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{
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"Home": "/graph/home/path",
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"Opts": [],
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"UIDMaps": [],
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"GIDMaps": []
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}
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```
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Initialize the graph driver plugin with a home directory and array of options.
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These are passed through from the user, but the plugin is not required to parse
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or honor them.
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The request also includes a list of UID and GID mappings, structed as follows:
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```json
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{
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"ContainerID": 0,
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"HostID": 0,
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"Size": 0
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}
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```
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**Response**:
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```json
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{
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"Err": ""
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}
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```
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Respond with a non-empty string error if an error occurred.
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### /GraphDriver.Capabilities
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**Request**:
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```json
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{}
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```
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Get behavioral characteristics of the graph driver. If a plugin does not handle
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this request, the engine will use default values for all capabilities.
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**Response**:
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```json
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{
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"ReproducesExactDiffs": false,
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}
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```
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Respond with values of capabilities:
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* **ReproducesExactDiffs** Defaults to false. Flags that this driver is capable
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of reproducing exactly equivalent diffs for read-only filesystem layers.
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### /GraphDriver.Create
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**Request**:
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```json
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{
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"ID": "46fe8644f2572fd1e505364f7581e0c9dbc7f14640bd1fb6ce97714fb6fc5187",
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"Parent": "2cd9c322cb78a55e8212aa3ea8425a4180236d7106938ec921d0935a4b8ca142",
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"MountLabel": "",
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"StorageOpt": {}
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}
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```
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Create a new, empty, read-only filesystem layer with the specified
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`ID`, `Parent` and `MountLabel`. If `Parent` is an empty string, there is no
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parent layer. `StorageOpt` is map of strings which indicate storage options.
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**Response**:
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```json
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{
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"Err": ""
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}
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```
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Respond with a non-empty string error if an error occurred.
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### /GraphDriver.CreateReadWrite
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**Request**:
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```json
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{
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"ID": "46fe8644f2572fd1e505364f7581e0c9dbc7f14640bd1fb6ce97714fb6fc5187",
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"Parent": "2cd9c322cb78a55e8212aa3ea8425a4180236d7106938ec921d0935a4b8ca142",
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"MountLabel": "",
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"StorageOpt": {}
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}
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```
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Similar to `/GraphDriver.Create` but creates a read-write filesystem layer.
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### /GraphDriver.Remove
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**Request**:
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```json
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{
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"ID": "46fe8644f2572fd1e505364f7581e0c9dbc7f14640bd1fb6ce97714fb6fc5187"
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}
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```
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Remove the filesystem layer with this given `ID`.
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**Response**:
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```json
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{
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"Err": ""
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}
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```
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Respond with a non-empty string error if an error occurred.
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### /GraphDriver.Get
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**Request**:
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```json
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{
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"ID": "46fe8644f2572fd1e505364f7581e0c9dbc7f14640bd1fb6ce97714fb6fc5187",
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"MountLabel": ""
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}
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```
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Get the mountpoint for the layered filesystem referred to by the given `ID`.
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**Response**:
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```json
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{
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"Dir": "/var/mygraph/46fe8644f2572fd1e505364f7581e0c9dbc7f14640bd1fb6ce97714fb6fc5187",
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"Err": ""
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}
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```
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Respond with the absolute path to the mounted layered filesystem.
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Respond with a non-empty string error if an error occurred.
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### /GraphDriver.Put
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**Request**:
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```json
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{
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"ID": "46fe8644f2572fd1e505364f7581e0c9dbc7f14640bd1fb6ce97714fb6fc5187"
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}
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```
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Release the system resources for the specified `ID`, such as unmounting the
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filesystem layer.
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**Response**:
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```json
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{
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"Err": ""
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}
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```
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Respond with a non-empty string error if an error occurred.
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### /GraphDriver.Exists
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**Request**:
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```json
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{
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"ID": "46fe8644f2572fd1e505364f7581e0c9dbc7f14640bd1fb6ce97714fb6fc5187"
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}
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```
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Determine if a filesystem layer with the specified `ID` exists.
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**Response**:
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```json
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{
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"Exists": true
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}
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```
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Respond with a boolean for whether or not the filesystem layer with the specified
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`ID` exists.
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### /GraphDriver.Status
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**Request**:
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```json
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{}
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```
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Get low-level diagnostic information about the graph driver.
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**Response**:
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```json
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{
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"Status": [[]]
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}
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```
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Respond with a 2-D array with key/value pairs for the underlying status
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information.
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### /GraphDriver.GetMetadata
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**Request**:
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```json
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{
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"ID": "46fe8644f2572fd1e505364f7581e0c9dbc7f14640bd1fb6ce97714fb6fc5187"
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}
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```
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Get low-level diagnostic information about the layered filesystem with the
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with the specified `ID`
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**Response**:
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```json
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{
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"Metadata": {},
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"Err": ""
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}
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```
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Respond with a set of key/value pairs containing the low-level diagnostic
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information about the layered filesystem.
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Respond with a non-empty string error if an error occurred.
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### /GraphDriver.Cleanup
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**Request**:
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```json
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{}
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```
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Perform necessary tasks to release resources help by the plugin, such as
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unmounting all the layered file systems.
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**Response**:
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```json
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{
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"Err": ""
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}
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```
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Respond with a non-empty string error if an error occurred.
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### /GraphDriver.Diff
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**Request**:
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```json
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{
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"ID": "46fe8644f2572fd1e505364f7581e0c9dbc7f14640bd1fb6ce97714fb6fc5187",
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"Parent": "2cd9c322cb78a55e8212aa3ea8425a4180236d7106938ec921d0935a4b8ca142"
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}
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```
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Get an archive of the changes between the filesystem layers specified by the `ID`
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and `Parent`. `Parent` may be an empty string, in which case there is no parent.
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**Response**:
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```
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{% raw %}
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{{ TAR STREAM }}
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{% endraw %}
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```
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### /GraphDriver.Changes
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**Request**:
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```json
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{
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"ID": "46fe8644f2572fd1e505364f7581e0c9dbc7f14640bd1fb6ce97714fb6fc5187",
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"Parent": "2cd9c322cb78a55e8212aa3ea8425a4180236d7106938ec921d0935a4b8ca142"
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}
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```
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Get a list of changes between the filesystem layers specified by the `ID` and
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`Parent`. If `Parent` is an empty string, there is no parent.
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**Response**:
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```json
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{
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"Changes": [{}],
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"Err": ""
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}
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```
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Respond with a list of changes. The structure of a change is:
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```json
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"Path": "/some/path",
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"Kind": 0,
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```
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Where the `Path` is the filesystem path within the layered filesystem that is
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changed and `Kind` is an integer specifying the type of change that occurred:
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- 0 - Modified
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- 1 - Added
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- 2 - Deleted
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Respond with a non-empty string error if an error occurred.
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### /GraphDriver.ApplyDiff
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**Request**:
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```
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{% raw %}
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{{ TAR STREAM }}
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{% endraw %}
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```
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Extract the changeset from the given diff into the layer with the specified `ID`
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and `Parent`
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**Query Parameters**:
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- id (required)- the `ID` of the new filesystem layer to extract the diff to
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- parent (required)- the `Parent` of the given `ID`
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**Response**:
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```json
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{
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"Size": 512366,
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"Err": ""
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}
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```
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Respond with the size of the new layer in bytes.
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Respond with a non-empty string error if an error occurred.
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### /GraphDriver.DiffSize
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**Request**:
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```json
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{
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"ID": "46fe8644f2572fd1e505364f7581e0c9dbc7f14640bd1fb6ce97714fb6fc5187",
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"Parent": "2cd9c322cb78a55e8212aa3ea8425a4180236d7106938ec921d0935a4b8ca142"
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}
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```
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Calculate the changes between the specified `ID`
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**Response**:
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```json
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{
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"Size": 512366,
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"Err": ""
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}
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```
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Respond with the size changes between the specified `ID` and `Parent`
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Respond with a non-empty string error if an error occurred.
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