Loading autotestPrivate extension on your device

AutotestPrivate is an extension that exposes APIs that facilitate the interaction with a Chrome OS device during tests. This guide shows how to load the extension on your device.


You need a device running a Chrome OS test image and a Chromium OS checkout. To load a test image on your device follow these steps from the Simple Chrome guide. To grab a checkout of Chromium OS follow the OS Developer Guide.

Removing rootfs verification and editing command line flags

NOTE: If you've completed these steps before feel free to skip to Loading autotest extension on your device

To get a command shell on the device:

  1. Run in your workstation:

    ssh root@$IP_ADDR

    Use the default password:


  2. To run Chrome OS with flags, first make usr partition writeable with:

    /usr/share/vboot/bin/make_dev_ssd.sh --remove_rootfs_verification --partitions 2
    /usr/share/vboot/bin/make_dev_ssd.sh --remove_rootfs_verification --partitions 4
  3. Reboot your device for rootfs changes to take effect. Run:


  4. Then append desired flags(listed below) to /etc/chrome_dev.conf.

Loading autotest extension on your device

  1. Enter a Chrome OS chroot. Inside of your Chrome OS checkout directory run:


  2. From inside your Chrome OS chroot run:

    test_that $IP_ADDR -b $BOARD dummy_Pass

    This will install the autotestPrivate extension manifest to your device.

  3. Open a command prompt in your device and edit your command line flags.

    • Add flag --remote-debugging-port=9333
      • NOTE: Port 9333 is not required, any port will work.
    • Add flag --load-extension=/usr/local/autotest/common_lib/cros/autotest_private_ext
  4. In your device's command prompt run

    restart ui

    for flag changes to take effect.

  5. Ssh to your device with ssh -L 9333:localhost:9333 root@$IP_ADDR

    This will forward your device's devtools port to a local port on your workstation.

  6. On your workstation, point your browser to localhost:9333.

  7. Click on Telemetry ChromeOS AutoTest Component Extension. This opens a connection to the extension's backgound page.

  8. Open the console tab.

If you've followed all the steps correctly, you should be able to execute code in the console tab to interact with the extension.

For example, try running:

> chrome.autotestPrivate.loginStatus(status => console.log(status));
> {isLoggedIn: false, isOwner: false, isReadyForPassword: false, isScreenLocked: false}