title: How to solve the error, Failed to launch emulator. Reason: No emulators found as an output of `emulator -list-avds` in React native?
body: <p>I am creating react native app for mobile application. I am fully new in building react native app. I am using ubuntu for creating the app and following below link to create the app.
  <a href="https://facebook.github.io/react-native/docs/getting-started" rel="noreferrer">https://facebook.github.io/react-native/docs/getting-started</a> . Can anyone please solve the issue ?</p>
  
  <p>At below stage I am getting error:</p>
  
  <pre><code>cd AwesomeProject
  npx react-native run-android
  </code></pre>
  
  <p>Error in my command line:</p>
  
  <pre><code>All-Series:~/Projects_App/AwesomeProject$ npx react-native run-android
  info Running jetifier to migrate libraries to AndroidX. You can disable it using "--no-jetifier" flag.
  Jetifier found 864 file(s) to forward-jetify. Using 4 workers...
  info Starting JS server...
  /bin/sh: 1: adb: not found
  info Launching emulator...
  error Failed to launch emulator. Reason: No emulators found as an output of `emulator -list-avds`.
  warn Please launch an emulator manually or connect a device. Otherwise app may fail to launch.
  info Installing the app...
  &gt; Task :app:compileDebugJavaWithJavac FAILED
  
  Deprecated Gradle features were used in this build, making it incompatible with Gradle 6.0.
  Use '--warning-mode all' to show the individual deprecation warnings.
  See https://docs.gradle.org/5.5/userguide/command_line_interface.html#sec:command_line_warnings
  13 actionable tasks: 4 executed, 9 up-to-date
  
  FAILURE: Build failed with an exception.
  
  * What went wrong:
  Execution failed for task ':app:compileDebugJavaWithJavac'.
  &gt; Could not find tools.jar. Please check that /usr/lib/jvm/java-8-openjdk-amd64 contains a valid JDK installation.
  
  * Try:
  Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
  
  * Get more help at https://help.gradle.org
  
  BUILD FAILED in 5s
  
  error Failed to install the app. Make sure you have the Android development environment set up: https://facebook.github.io/react-native/docs/getting-started.html#android-development-environment. Run CLI with --verbose flag for more details.
  Error: Command failed: ./gradlew app:installDebug -PreactNativeDevServerPort=8081
  
  FAILURE: Build failed with an exception.
  
  * What went wrong:
  Execution failed for task ':app:compileDebugJavaWithJavac'.
  &gt; Could not find tools.jar. Please check that /usr/lib/jvm/java-8-openjdk-amd64 contains a valid JDK installation.
  
  * Try:
  Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
  
  * Get more help at https://help.gradle.org
  
  BUILD FAILED in 5s
  
      at checkExecSyncError (child_process.js:621:11)
      at execFileSync (child_process.js:639:15)
      at runOnAllDevices (/home/rupeevest/Projects_App/AwesomeProject/node_modules/@react-native-community/cli-platform-android/build/commands/runAndroid/runOnAllDevices.js:94:39)
      at processTicksAndRejections (internal/process/task_queues.js:93:5)
  </code></pre>