mirror of https://github.com/docker/cli.git
264 lines
10 KiB
Markdown
264 lines
10 KiB
Markdown
---
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title: Docker Engine managed plugin system
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description: Develop and use a plugin with the managed plugin system
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keywords: "API, Usage, plugins, documentation, developer"
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---
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- [Installing and using a plugin](index.md#installing-and-using-a-plugin)
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- [Developing a plugin](index.md#developing-a-plugin)
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- [Debugging plugins](index.md#debugging-plugins)
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Docker Engine's plugin system lets you install, start, stop, and remove
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plugins using Docker Engine.
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For information about legacy (non-managed) plugins, refer to
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[Understand legacy Docker Engine plugins](legacy_plugins.md).
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> **Note**
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>
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> Docker Engine managed plugins are currently not supported on Windows daemons.
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## Installing and using a plugin
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Plugins are distributed as Docker images and can be hosted on Docker Hub or on
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a private registry.
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To install a plugin, use the `docker plugin install` command, which pulls the
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plugin from Docker Hub or your private registry, prompts you to grant
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permissions or capabilities if necessary, and enables the plugin.
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To check the status of installed plugins, use the `docker plugin ls` command.
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Plugins that start successfully are listed as enabled in the output.
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After a plugin is installed, you can use it as an option for another Docker
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operation, such as creating a volume.
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In the following example, you install the `sshfs` plugin, verify that it is
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enabled, and use it to create a volume.
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> **Note**
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>
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> This example is intended for instructional purposes only. Once the volume is
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> created, your SSH password to the remote host is exposed as plaintext when
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> inspecting the volume. Delete the volume as soon as you are done with the
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> example.
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1. Install the `sshfs` plugin.
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```console
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$ docker plugin install vieux/sshfs
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Plugin "vieux/sshfs" is requesting the following privileges:
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- network: [host]
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- capabilities: [CAP_SYS_ADMIN]
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Do you grant the above permissions? [y/N] y
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vieux/sshfs
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```
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The plugin requests 2 privileges:
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- It needs access to the `host` network.
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- It needs the `CAP_SYS_ADMIN` capability, which allows the plugin to run
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the `mount` command.
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2. Check that the plugin is enabled in the output of `docker plugin ls`.
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```console
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$ docker plugin ls
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ID NAME TAG DESCRIPTION ENABLED
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69553ca1d789 vieux/sshfs latest the `sshfs` plugin true
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```
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3. Create a volume using the plugin.
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This example mounts the `/remote` directory on host `1.2.3.4` into a
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volume named `sshvolume`.
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This volume can now be mounted into containers.
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```console
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$ docker volume create \
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-d vieux/sshfs \
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--name sshvolume \
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-o sshcmd=user@1.2.3.4:/remote \
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-o password=$(cat file_containing_password_for_remote_host)
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sshvolume
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```
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4. Verify that the volume was created successfully.
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```console
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$ docker volume ls
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DRIVER NAME
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vieux/sshfs sshvolume
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```
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5. Start a container that uses the volume `sshvolume`.
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```console
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$ docker run --rm -v sshvolume:/data busybox ls /data
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<content of /remote on machine 1.2.3.4>
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```
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6. Remove the volume `sshvolume`
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```console
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$ docker volume rm sshvolume
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sshvolume
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```
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To disable a plugin, use the `docker plugin disable` command. To completely
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remove it, use the `docker plugin remove` command. For other available
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commands and options, see the
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[command line reference](https://docs.docker.com/engine/reference/commandline/cli/).
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## Developing a plugin
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#### The rootfs directory
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The `rootfs` directory represents the root filesystem of the plugin. In this
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example, it was created from a Dockerfile:
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> **Note**
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>
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> The `/run/docker/plugins` directory is mandatory inside of the
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> plugin's filesystem for Docker to communicate with the plugin.
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```console
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$ git clone https://github.com/vieux/docker-volume-sshfs
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$ cd docker-volume-sshfs
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$ docker build -t rootfsimage .
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$ id=$(docker create rootfsimage true) # id was cd851ce43a403 when the image was created
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$ sudo mkdir -p myplugin/rootfs
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$ sudo docker export "$id" | sudo tar -x -C myplugin/rootfs
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$ docker rm -vf "$id"
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$ docker rmi rootfsimage
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```
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#### The config.json file
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The `config.json` file describes the plugin. See the [plugins config reference](config.md).
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Consider the following `config.json` file.
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```json
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{
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"description": "sshFS plugin for Docker",
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"documentation": "https://docs.docker.com/engine/extend/plugins/",
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"entrypoint": ["/docker-volume-sshfs"],
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"network": {
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"type": "host"
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},
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"interface": {
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"types": ["docker.volumedriver/1.0"],
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"socket": "sshfs.sock"
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},
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"linux": {
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"capabilities": ["CAP_SYS_ADMIN"]
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}
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}
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```
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This plugin is a volume driver. It requires a `host` network and the
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`CAP_SYS_ADMIN` capability. It depends upon the `/docker-volume-sshfs`
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entrypoint and uses the `/run/docker/plugins/sshfs.sock` socket to communicate
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with Docker Engine. This plugin has no runtime parameters.
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#### Creating the plugin
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A new plugin can be created by running
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`docker plugin create <plugin-name> ./path/to/plugin/data` where the plugin
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data contains a plugin configuration file `config.json` and a root filesystem
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in subdirectory `rootfs`.
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After that the plugin `<plugin-name>` will show up in `docker plugin ls`.
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Plugins can be pushed to remote registries with
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`docker plugin push <plugin-name>`.
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## Debugging plugins
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Stdout of a plugin is redirected to dockerd logs. Such entries have a
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`plugin=<ID>` suffix. Here are a few examples of commands for pluginID
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`f52a3df433b9aceee436eaada0752f5797aab1de47e5485f1690a073b860ff62` and their
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corresponding log entries in the docker daemon logs.
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```console
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$ docker plugin install tiborvass/sample-volume-plugin
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INFO[0036] Starting... Found 0 volumes on startup plugin=f52a3df433b9aceee436eaada0752f5797aab1de47e5485f1690a073b860ff62
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```
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```console
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$ docker volume create -d tiborvass/sample-volume-plugin samplevol
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INFO[0193] Create Called... Ensuring directory /data/samplevol exists on host... plugin=f52a3df433b9aceee436eaada0752f5797aab1de47e5485f1690a073b860ff62
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INFO[0193] open /var/lib/docker/plugin-data/local-persist.json: no such file or directory plugin=f52a3df433b9aceee436eaada0752f5797aab1de47e5485f1690a073b860ff62
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INFO[0193] Created volume samplevol with mountpoint /data/samplevol plugin=f52a3df433b9aceee436eaada0752f5797aab1de47e5485f1690a073b860ff62
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INFO[0193] Path Called... Returned path /data/samplevol plugin=f52a3df433b9aceee436eaada0752f5797aab1de47e5485f1690a073b860ff62
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```
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```console
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$ docker run -v samplevol:/tmp busybox sh
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INFO[0421] Get Called... Found samplevol plugin=f52a3df433b9aceee436eaada0752f5797aab1de47e5485f1690a073b860ff62
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INFO[0421] Mount Called... Mounted samplevol plugin=f52a3df433b9aceee436eaada0752f5797aab1de47e5485f1690a073b860ff62
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INFO[0421] Path Called... Returned path /data/samplevol plugin=f52a3df433b9aceee436eaada0752f5797aab1de47e5485f1690a073b860ff62
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INFO[0421] Unmount Called... Unmounted samplevol plugin=f52a3df433b9aceee436eaada0752f5797aab1de47e5485f1690a073b860ff62
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```
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#### Using runc to obtain logfiles and shell into the plugin.
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Use `runc`, the default docker container runtime, for debugging plugins by
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collecting plugin logs redirected to a file.
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```console
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$ sudo runc --root /run/docker/runtime-runc/plugins.moby list
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ID PID STATUS BUNDLE CREATED OWNER
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93f1e7dbfe11c938782c2993628c895cf28e2274072c4a346a6002446c949b25 15806 running /run/docker/containerd/daemon/io.containerd.runtime.v1.linux/moby-plugins/93f1e7dbfe11c938782c2993628c895cf28e2274072c4a346a6002446c949b25 2018-02-08T21:40:08.621358213Z root
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9b4606d84e06b56df84fadf054a21374b247941c94ce405b0a261499d689d9c9 14992 running /run/docker/containerd/daemon/io.containerd.runtime.v1.linux/moby-plugins/9b4606d84e06b56df84fadf054a21374b247941c94ce405b0a261499d689d9c9 2018-02-08T21:35:12.321325872Z root
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c5bb4b90941efcaccca999439ed06d6a6affdde7081bb34dc84126b57b3e793d 14984 running /run/docker/containerd/daemon/io.containerd.runtime.v1.linux/moby-plugins/c5bb4b90941efcaccca999439ed06d6a6affdde7081bb34dc84126b57b3e793d 2018-02-08T21:35:12.321288966Z root
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```
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```console
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$ sudo runc --root /run/docker/runtime-runc/plugins.moby exec 93f1e7dbfe11c938782c2993628c895cf28e2274072c4a346a6002446c949b25 cat /var/log/plugin.log
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```
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If the plugin has a built-in shell, then exec into the plugin can be done as
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follows:
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```console
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$ sudo runc --root /run/docker/runtime-runc/plugins.moby exec -t 93f1e7dbfe11c938782c2993628c895cf28e2274072c4a346a6002446c949b25 sh
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```
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#### Using curl to debug plugin socket issues.
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To verify if the plugin API socket that the docker daemon communicates with
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is responsive, use curl. In this example, we will make API calls from the
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docker host to volume and network plugins using curl 7.47.0 to ensure that
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the plugin is listening on the said socket. For a well functioning plugin,
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these basic requests should work. Note that plugin sockets are available on the host under `/var/run/docker/plugins/<pluginID>`
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```console
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$ curl -H "Content-Type: application/json" -XPOST -d '{}' --unix-socket /var/run/docker/plugins/e8a37ba56fc879c991f7d7921901723c64df6b42b87e6a0b055771ecf8477a6d/plugin.sock http:/VolumeDriver.List
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{"Mountpoint":"","Err":"","Volumes":[{"Name":"myvol1","Mountpoint":"/data/myvol1"},{"Name":"myvol2","Mountpoint":"/data/myvol2"}],"Volume":null}
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```
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```console
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$ curl -H "Content-Type: application/json" -XPOST -d '{}' --unix-socket /var/run/docker/plugins/45e00a7ce6185d6e365904c8bcf62eb724b1fe307e0d4e7ecc9f6c1eb7bcdb70/plugin.sock http:/NetworkDriver.GetCapabilities
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{"Scope":"local"}
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```
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When using curl 7.5 and above, the URL should be of the form
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`http://hostname/APICall`, where `hostname` is the valid hostname where the
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plugin is installed and `APICall` is the call to the plugin API.
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For example, `http://localhost/VolumeDriver.List`
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