open-nomad/website/content/docs/concepts/plugins/base.mdx

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---
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layout: docs
page_title: Base Plugin
description: Learn about how to author a Nomad plugin.
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---
# Base Plugin
The base plugin is a special plugin type implemented by all plugins. It allows
for common plugin operations such as defining a configuration schema and
version information.
## Plugin API
#### `PluginInfo() (*PluginInfoResponse, error)`
A `PluginInfoResponse` contains meta data about the plugin.
```go
PluginInfoResponse{
// Type is the plugin type which is implemented
Type: PluginTypeDriver,
// Plugin API versions supported by the plugin
PluginApiVersions: []string{drivers.ApiVersion010},
// Version of the plugin
PluginVersion: "0.1.0",
// Name of the plugin
Name: "foodriver",
}
```
#### `ConfigSchema() (*hclspec.Spec, error)`
The `ConfigSchema` function allows a plugin to tell Nomad the schema for its
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configuration. This configuration is given in a [plugin block][pluginblock] of
the client configuration. The schema is defined with the [hclspec][hclspec]
package.
#### `SetConfig(config *Config) error`
The `SetConfig` function is called when starting the plugin for the first
time. The `Config` given has two different configuration fields. The first
`PluginConfig`, is an encoded configuration from the `plugin` block of the
client config. The second, `AgentConfig`, is the Nomad agent's configuration
which is given to all plugins.
## HCL Specifications
`*hclspec.Spec` is a struct that defines the schema to validate an HCL entity
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against. The full documentation of the different hcl attribute types can be
found on the [hclspec godoc][hclspec].
For a basic example, lets look at the driver configuration for the raw_exec
driver:
```hcl
job "example" {
...
driver = "raw_exec"
config {
command = "/bin/sleep"
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args = ["100"]
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}
}
```
The `config` block is what is validated against the `hclspec.Spec`. It has two
keys, command which takes a string attribute and args which takes an array
attribute. The corresponding `*hclspec.Spec` would be:
```go
spec := hclspec.NewObject(map[string]*hclspec.Spec{
"command": hclspec.NewAttr("command", "string", true),
"args": hclspec.NewAttr("args", "list(string)", false),
})
```
[hclspec]: https://godoc.org/github.com/hashicorp/nomad/plugins/shared/hclspec
[pluginblock]: /nomad/docs/configuration/plugin