DockerCLI/docs/extend/plugins_graphdriver.md

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