docs/development/sessions/building-and-running-a-session.md

# Building and running a session {#building-and-running-a-session} 

A session is the first product-specific component started on boot. The session
component is responsible for building a product's user experience. For more
information on sessions, see
[session framework](/docs/concepts/session/introduction.md).

## Booting into a session {#booting-into-a-session}

To boot into a session, do the following:

1. For a session to run at boot you need to create a configuration file with the
session component URL.

   <pre><code>{
       "session_url": "fuchsia-pkg://fuchsia.com/<var>pkg-name</var>#meta/<var>your_session.cm</var>"
   }</code></pre>

   Replace the following:
   * <var>pkg-name</var>: the package name
   * <var>your_session.cm</var>: the name of your session, including the `.cm`
   extension.

   For more information, see
   [`fuchsia-pkg`](/docs/concepts/components/component_urls.md#fuchsia-pkg) and
   [Package name](/docs/concepts/packages/package_url.md#package-name).

1.  In the `BUILD.gn` file, include the configuration file for the session
component

   ```json
   import("//src/session/build/session_config.gni")

   session_config("your_session_config") {
       config = "path/to/config.json"
   }
   ```

1. Run the following command to include the `session_manager`, `your_session`,
   and `:your_session_config` in your base image:

   <pre class="prettyprint"><code class="devsite-terminal">fx set <var>product</var>.<var>board</var> --with-base=//src/session,<var>//path/to/your/session</var>,<var>//path/to/your/session:your_session_config</var></code></pre>

   Note: Selecting a product that already has a session_config will result
   in a build error because the configurations will conflict. The `core`
   product would be a good choice as a starting point as it includes only the
   bare minimum needed to launch Fuchsia.

   `fx list-products` and `fx list-boards` will show lists of the products and
   boards available to be used in the `fx set` command. For more information on
   `fx` commands see the [fx documentation](/docs/development/build/fx.md).

1. Rebuild and re-pave the device.

   ```posix-terminal
   fx build
   fx ota
   ```

   This causes `session_manager` to start and launch your session.

For a full explanation of building a session component, see [Writing a Hello
World Session](/docs/development/sessions/writing-a-hello-world-session.md).

## Launch a session from the command line {#launch-a-session-from-the-command-line}

There are cases when you don't want your session to launch at boot but still
want to be able to launch it from the command line. There still needs to be a
session launched at boot so configure the build to use the default
`session_manager` configuration.

To launch a session from the command line, do the following:

1. Run the following command to include the `session_manager` and the
`session_manager` configuration file, `session_manager.config`, in the base
image while also including your session in the build.

   <pre class="prettyprint"><code class="devsite-terminal">fx set <var>product</var>.<var>board</var> --with-base=//src/session,//src/session/bin/session_manager:session_manager.config --with=<var>//path/to/your/session</var></code></pre>

   `fx list-products` and `fx list-boards` will show lists of the products and
   boards available to be used in the `fx set` command. For more information on
   `fx` commands see the [fx documentation](/docs/development/build/fx.md).

1. Run the following command to rebuild and repave the device:

   ```posix-terminal
   fx build
   fx ota
   ```

   This causes `session_manager` to start without launching your session.

1. Your session can now be launched from the command line.

   Run the following command to launch your session:

   <pre class="prettyprint"><code class="devsite-terminal">ffx session launch fuchsia-pkg://fuchsia.com/<var>pkg-name</var>#meta/<var>your_session.cm</var></code></pre>

   For more information about the `ffx session` command, run
   `ffx session --help`. For more information about `ffx`, see the
   [`ffx documentation`](/docs/development/tools/ffx/overview.md).