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## ⁠2.16. Runtime

### ⁠2.16.1. Introduction

Components of type `runtime` describe a collection of interdependent software components that are required to run other software. They set a baseline of dependencies that other software can rely on and link against. A very simple runtime may for example be a chroot environment of a minimal Linux system bootstrap. Runtimes are often employed by software distribution systems such as Flatpak or Valve's Steam, but may be used by others and may even be directly distributed as part of tranditional Linux distributions.
Runtimes can ship metainfo files in `/usr/share/metainfo/%{id}.metainfo.xml`.

### ⁠2.16.2. Example file

A `runtime` metainfo file can look like this:

    ​
    ​<?xml version="1.0" encoding="UTF-8"?>
    ​<component type="runtime">
    ​  <id>org.freedesktop.Platform</id>
    ​  <metadata_license>FSFAP</metadata_license>
    ​  <project_license>LicenseRef-free=https://freedesktop-sdk.gitlab.io/</project_license>
    ​
    ​  <name>Freedesktop Platform</name>
    ​  <summary>Basic libraries to run Linux desktop applications</summary>
    ​
    ​  <description>
    ​    <p>
    ​      The Freedesktop Platform is a runtime that contains the most basic libraries
    ​      and files needed to run a Linux desktop application.
    ​      ...
    ​    </p>
    ​  </description>
    ​  <url type="homepage">https://freedesktop-sdk.gitlab.io/</url>
    ​
    ​  <releases>
    ​    <release version="10.0" />
    ​    <release version="9.0" date="2020-01-12" />
    ​    ...
    ​  </releases>
    ​</component>

### ⁠2.16.3. File specification

Note that the XML root must have the `type` property set to `runtime`. This clearly identifies this metainfo document as describing a runtime.

⁠<id/>
  For runtimes, the value of the `<id/>` tag must follow the AppStream ID naming conventions (it should be a reverse-DNS name).
⁠<requires/>
  The `requires` tag may be used if multiple runtimes are based on top of each other, or if the runtime actually describes a software development kit (SDK) that wants to require its base runtime. See <requires/> & <recommends/> for a detailed description of this tag.
  In order to depend on other runtimes, their component-ID should be referenced in a `requires` tag. Example:

      ​<requires>
      ​  <id version="1.0" compare="ge">org.freedesktop.Sdk</id>
      ​</requires>

⁠<project_license/>
  The `<project_license/>` tag usually indicates the license of the component (refer to <project_license/> for details). This is tricky for runtimes, as they are usually comprised of many individual pieces of software under different licenses, which would create a very long and complex SPDX license expression. It is therefore recommended to have the tool that builds the runtime collect all the licenses and generate a document or website containing. This document can then be linked using `LicenseRef-free=URL` if the runtime is free software, or `LicenseRef-proprietary=URL` in case it contains non-free elements.
  Example:

      ​<project_license>LicenseRef-free=https://example.com/licenses.html</project_license>

⁠<provides/>
  This tag is described in detail for generic components at <provides/>.
  The runtime may use the `<provides/>` tag to denote the individual modules it is comprised of, using their component IDs.

For a component of type `runtime`, the following tags are required and must be present for a valid document: <id/>, <name/>, <summary/>, <metadata_license/>, <project_license/>.

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