64 lines
2.4 KiB
Markdown
64 lines
2.4 KiB
Markdown
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---
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page_title: "Host Capabilities - Plugin Development"
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sidebar_current: "plugins-hostcapabilities"
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---
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# Plugin Development: Host Capabilities
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This page documents how to add new capabilities for [hosts](/v2/plugins/hosts.html)
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to Vagrant, allowing Vagrant to perform new actions on specific host
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operating systems.
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Prior to reading this, you should be familiar
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with the [plugin development basics](/v2/plugins/development-basics.html).
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<div class="alert alert-warn">
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<p>
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<strong>Warning: Advanced Topic!</strong> Developing plugins is an
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advanced topic that only experienced Vagrant users who are reasonably
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comfortable with Ruby should approach.
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</p>
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</div>
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Host capabilities augment [hosts](/v2/plugins/hosts.html) by attaching
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specific "capabilities" to the host, which are actions that can be performed
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in the context of that host operating system.
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The power of capabilities is that plugins can add new capabilities to
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existing host operating systems without modifying the core of Vagrant.
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In earlier versions of Vagrant, all the host logic was contained in the
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core of Vagrant and wasn't easily augmented.
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## Definition and Implementation
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The definition and implementation of host capabilities is identical
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to [guest capabilities](/v2/plugins/guest-capabilities.html).
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The main difference from guest capabilities, however, is that instead of
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taking a machine as the first argument, all host capabilities take an
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instance of `Vagrant::Environment` as their first argument.
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Access to the environment allows host capabilities to access global state,
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specific machines, and also allows them to call other host capabilities.
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## Calling Capabilities
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Since you have access to the environment in every capability, capabilities can
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also call _other_ host capabilities. This is useful for using the inheritance
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mechanism of capabilities to potentially ask helpers for more information.
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For example, the "linux" guest has a "nfs\_check\_command" capability that
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returns the command to use to check if NFS is running.
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Capabilities on child guests of Linux such as RedHat or Arch use this
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capability to mostly inherit the Linux behavior, except for this minor
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detail.
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Capabilities can be called like so:
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```ruby
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environment.host.capability(:capability_name)
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```
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Any additional arguments given to the method will be passed on to the
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capability, and the capability will return the value that the actual
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capability returned.
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