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Setup your development Chromebook

Don’t have a development Chromebook yet? Skim this section and then move on to Checkout Chromium. From there you can learn about development flows that do not require a Chromebook, e.g., building and running ChromiumOS on Linux.

Download and flash a ChromiumOS test image onto the USB drive

Download the test image

The cros flash tool supports downloading ChromiumOS images built regularly and stored in Google Storage. The xbuddy URL format allows specifying images by board, version, and image type. The default xbuddy format downloads the latest test image for the specified board. You can determine your board by navigating to chrome://version on your development Chromebook; it’s the last word of “Platform”. Run the following command in your Chromium or ChromiumOS source checkout, replacing <board> appropriately, to download the latest test image for your board in the current directory.

$ cros flash file://`pwd`/chromium_test_image.bin xbuddy://remote/<board>/latest-dev

If you downloaded the image on a remote machine (e.g., a virtualized workstation) or in Crostini, you will need to move the image file to the local machine with which you will connect the USB drive (an SSH connection in Secure Shell is one option).

Alternatively, if you are working on your development workstation, you can directly flash the USB drive in one command (see below for more information about using cros flash to flash a USB drive).

$ cros flash usb:// xbuddy://remote/<board>/latest-dev

Flash the test image to your USB drive

On a workstation

Plug the USB drive into your development workstation then run:

$ cros flash usb:// ./chromiumos_test_image.bin

Note: If cros flash can’t automagically find your USB drive, you may need to use a different USB drive. If you must use that given USB drive, troubleshoot using the cros flash documentation.

Note: If you need to flash a different test image to the same USB drive later, simply run cros flash ... as before; no extra steps are necessary.

The USB drive now contains the test image and is ready to be flashed to the Chromebook. The next section goes over how to prepare the Chromebook for flashing and the steps to flash the device.

On a Chromebook or Mac

To flash the test image to a USB drive if you're working on a Chromebook:

  1. Plug the USB drive into your Chromebook.
  2. Install and launch the “Chromebook Recovery Utility” extension (documentation).
  3. Click the gear icon and select "Use local image".
  4. Select the .bin image you downloaded previously.
  5. Proceed through the prompts.

If the prompts get stuck at erasing or writing to your recovery media, then you are likely restricted to read-only on USB storage. See Removable media storage restrictions for more information and how to request an exception to get past this.

Put your chromebook into developer mode

In order to flash your chromebook from the USB drive, the Chromebook needs to be in developer mode.

Developer Mode

To put the chromebook in developer mode, press (you will likely need to hold down this combo for ~4 seconds):

esc + Refresh (f3) + power

Note: Some devices, such as Eve/Atlas, have the Refresh button bound to F2. When in doubt, use the refresh button for this step.

Note: For some devices, like newer brya devices, tap the power button while holding down esc + Refresh (f2).

Note: For tablets, such as Nocturne, press both the increase and decrease volume buttons and the power button to enter developer mode. You must use the buttons on the actual tablet and not the ones on any attached keyboard. If the recovery menu shows up, you can use the same volume buttons to navigate and the power button to make selections; press both volume buttons simultaneously to open the hidden developer mode menu (see go/tablet-dev for more information).

Note: For some devices, such as Teemo, keep the recovery button pressed (press pin or paper clip inside small hole located on the right side of the box) while pressing power button to go into recovery mode.

Once the device boots up and the developer screen shows up, press ctrl-d to boot from disk.

If the device boots to the recovery screen, press ctrl-d to enter developer mode. You should see "OS Verification turned OFF". From this point on, never hit Spacebar to disable Developer Mode as the screen suggests you do.

After booting from disk, open the VT2 terminal by pressing:

ctrl + alt + Forward (f2)

Note: Some devices, such as Eve/Atlas, are missing a Forward button, with another button (refresh) in the F2 place. When in doubt, still use the F2 button for this step.

You can usually locate the correct button by counting the function keys left-to-right (disregard the esc key).

The VT2 terminal can be escaped by pressing

ctrl + alt + backward (f1)

Login as root. There should be no password.

(If there is a password, it may be test0000, as you may already be on a test image, in which case, you probably don’t need to follow these steps, unless you are trying to update to a newer test image.)

Note: The VT2 prompt suggests that you change the chronos password, but do not do this.

Note: When development mode is enabled, you can also access a prettier-terminal in ChromeOS by logging in (or pressing “Browse as Guest”), pressing `ctrl + alt

Note: If you are using a tablet without an attached keyboard, you will need to use crosh (see above) instead of VT2.

Allow booting from a flashdrive in the VT2 terminal, then reboot:

$ crossystem dev_boot_usb=1
$ reboot

Flash the test image to your Chromebook

Your device should now be in developer mode and be bootable from external media. Plug the USB drive with the test image on it (see section "Download and flash a ChromiumOS test image onto the USB drive") into the Chromebook, and at the developer screen on boot, press

ctrl + u

(Instead of ctrl + d)

This boots the Chromebook from the USB drive. Once you’ve booted from the USB drive, open the VT2 terminal again, login as root (the password will be test0000 this time), and run:

$ chromeos-install

This copies the contents of the USB drive onto the Chromebook’s drive, i.e. installs the test image onto it. This can take a few minutes to complete. Once finished, reboot:

$ reboot

Boot from disk (ctrl + d) and then remove the USB drive (you won’t need it again until you need to repeat this process). You’re now running the test image!

IMPORTANT: once you have flashed a test image to your chromebook, avoid logging into the device with an important account (especially a corp account). The root password is public knowledge, so consider the device easily compromised. It is okay to occasionally log in with important accounts, but do so sparingly, and immediately wipe the account off the machine once finished. You should generally only be using test accounts (see "Owned Test Accounts"). If you need to restore the machine to be corp safe, follow steps 2 and 3 of “Restore your Chromebook” and steps 2 and 3 of “Reset or reimage a ChromeOS device”.

Help! chromeos-install is complaining it cannot determine a destination device

Some boards, including morphius boards, might have an issue where chromeos-install cannot find the correct destination drive when booting from USB. The error appears like so:

localhost$ chromeos-install
cros-disks stop/waiting
Error: can not determine destination device. Specify --dst yourself

This happens when the USB is being assigned as the dst (destination) incorrectly. To resolve this, specify the correct destination drive, like so:

localhost$ rootdev -s
localhost$ lsblk
loop0           7:0    0   552K  1 loop /run/chromeos-config/v1
loop1           7:1    0   1.2G  0 loop
`-encstateful 254:1    0   1.2G  0 dm   /home/chronos
loop2           7:2    0  94.2M  1 loop /usr/share/chromeos-assets/speech_synthesis/patts
loop3           7:3    0   9.2M  1 loop /usr/share/chromeos-assets/quickoffice/_platform_specific
loop4           7:4    0   6.5M  1 loop /usr/share/cros-camera/libfs
loop5           7:5    0  16.9M  1 loop
              254:2    0   6.5M  1 dm   /run/imageloader/nc-ap-dlc/package
sda             8:0    1  14.9G  0 disk
|-sda1          8:1    1     4G  0 part /var/cache/dlc-images
|                                       /var/lib/portage
|                                       /var/db/pkg
|                                       /usr/local
|                                       /home
|                                       /mnt/stateful_partition
|-sda2          8:2    1    32M  0 part
|-sda3          8:3    1   2.7G  0 part
|-sda4          8:4    1    32M  0 part
|-sda5          8:5    1     2M  0 part
|-sda6          8:6    1   512B  0 part
|-sda7          8:7    1   512B  0 part
|-sda8          8:8    1    16M  0 part /usr/share/oem
|-sda9          8:9    1   512B  0 part
|-sda10         8:10   1   512B  0 part
|-sda11         8:11   1   512B  0 part
`-sda12         8:12   1    64M  0 part
zram0         253:0    0  15.1G  0 disk [SWAP]
nvme0n1       259:0    0 238.5G  0 disk
|-nvme0n1p1   259:1    0 230.3G  0 part
|-nvme0n1p2   259:2    0    32M  0 part
|-nvme0n1p3   259:3    0     4G  0 part
|-nvme0n1p4   259:4    0    32M  0 part
|-nvme0n1p5   259:5    0     4G  0 part
|-nvme0n1p6   259:6    0   512B  0 part
|-nvme0n1p7   259:7    0   512B  0 part
|-nvme0n1p8   259:8    0    16M  0 part
|-nvme0n1p9   259:9    0   512B  0 part
|-nvme0n1p10  259:10   0   512B  0 part
|-nvme0n1p11  259:11   0   512B  0 part
`-nvme0n1p12  259:12   0    64M  0 part
localhost$ chromeos-install --dst /dev/nvme0n1

Connect your Chromebook to the internet

Your Chromebook must be connected to the internet so that your workstation (or Cloudtop) can remotely access it via ssh and change its binaries. How this is done depends on whether you are working from the office or from home.

Working from the office

Lab network is not available

Note: The lab network is not available in at least the following office:

  • TW-TPE-101 (as of August 2022)

The Lab network condition is varied (may still be under construction and only work in some areas), so please check with your neighbors. If in one of these offices, you should use these steps.

Googlers without a lab network available in their office can use 1 of 2 options to connect their test Chromebook to the internet / their workstation/cloudtop.

Use a hotspot on a phone Establish direct connection
Instructions go/hotspot-dut-deploy go/cros-direct-dut
Prerequisites Phone that supports hotspot Ethernet cable, two USB-to-ethernet port adapters
Pros Less hardware required More reliable connection
Cons Wi-Fi deploying can be less reliable More hardware required

Lab network is available

In US-LAX-BIN1, you need to plug your Chromebook into the purple port at your desk. If you don't have an available one, you can share a coworker's by using a switch.

Note: If you work from an office beside US-LAX, you'll need to ask around to understand if this guidance applies. Please update this page if this guidance needs adjusting for other offices.

This purple port at your desk should already be on the lab network. If ssh'ing from your workstation to your Chromebook as described above fails for you, ensure that your workstation is on SNAX by clicking the icon in the system tray of your workstation. If you're on SNAX and still can't SSH to your chromebook, your purple port is probably not on the lab network.

In order to get your purple port on the lab network, file a ticket (go/guts) and follow the format of this request here. You need to note down the number written above the purple jack and ask the techs to patch that port to the lax_cros_lab lab (as of December 2022, the switch name is US-LAX-BIN1-LABSW1-1-2).

Additional step for Cloudtop users

Cloudtop users can only access the lab network through a proxy. Run gcert to refresh your credentials, then use the ProxyCommand option when using SSH:

ssh -o "ProxyCommand=/usr/bin/corp-ssh-helper %h %p" root@<DUT IP address>

To avoid having to add this option whenever you use SSH, you can add the lab network subnet to your SSH config file ~/.ssh/config (the IP address is only an example!):

Match host 100.127.92.* exec "/usr/bin/corp-ssh-helper -check"
 ProxyCommand /usr/bin/corp-ssh-helper -direct_capable %h %p

Working from home

Connect your Chromebook to the same network that your corp laptop is connected to. It's recommended that you connect to this network via ethernet for deployment stability, but connecting via Wi-Fi works fine.

If you do connect via Wi-Fi, ensure that the network is available to all users on the device, so that when your primary user signs out (e.g., when Chrome is restarted during a deploy), the device remains connected to the network. You can ensure this by 1 of 2 ways:

SSH into your Chromebook

Google's Network access policy requires you to use one of two tools to connect to devices using SSH:

The corp SSH helper This tool works like the standard ssh command, and is used by the Secure Shell extension on ChromeOS.

The sshwatcher This tool will automatically reconnect to the remote device if the connection is dropped, e.g. the remote device reboots.

Step 0: Find your Chromebook's IP address

With your Chromebook now connected to the internet, it will be more convenient to remotely configure your Chromebook DUT via ssh. To do so, first find the Chromebook's IP address via:

$ ifconfig

The device's IP address is inet<address> value of the ethernet (or Wi-Fi if you connected wirelessly).

Note: An alternate way to view the device’s IP address is to log in, and click into the network setting of the Ethernet/Wi-Fi connection.

Working from the office: direct SSH

You can easily save this IP address for later use on your workstation/Cloudtop by saving it to an environment variable:

$ MYDEVICE=<address>

You can now ssh into the device. The root password for all test images is test0000:

$ ssh root@${MYDEVICE}

Working from home: SSH port forwarding

Connect your Chromebook to your home network (preferably over Ethernet for stability) and find the local IP address (for example, DUT_IP_ADDRESS= Make sure you connect to the network from the Chromebook login screen so that the network is not only configured for an individual account. From your ChromeOS corp machine, in the Secure Shell App, SSH to your workstation/cloudtop with this extra parameter in the "SSH Arguments" field on the configuration page:

-R 2233:<DUT_IP_ADDRESS>:22

See figure:

Port forwarding

This forwards the local IP address of your Chromebook, making it accessible on your workstation/cloudtop via localhost:2233.

You should now be able to ssh into the device. The root password for all test images is test0000:

[workstation]$ ssh root@localhost -p 2233


Port forwarding failed

If you see a Warning: remote port forwarding failed for listen port <PORT> message in the shell connection setup logs you may have a previous process still using the port. Try killing the process using sudo kill -9 $(sudo lsof -t -i:<PORT>) and restarting the shell.

You can optionally add the following helper function to your bash config to handle this in the future:

kill-pid-on-port() {
  if [ $# -eq 0 ]; then
    echo "Error: port number argument not provided"
    exit 0
  sudo kill -9 $(sudo lsof -t -i:$1)
Chromebook IP address changes frequently

If there is no possible way to connect directly with an Ethernet cable, you can attempt to configure the IP address manually in the event that the router keeps assigning a new one to the Chromebook. Go to the Chromebook's Network Settings, select the router you are connected to, and open the Network drop down panel. Toggle off the "Configure IP address automatically" and manually change the IP address to 192.168.1.X. The Chromebook will attempt to keep this IP address when restarting. Make sure to update the <DUT_IP_ADDRESS> SSH argument above to reflect your manually set IP address.

See figure where X is set to 111:

Manually set IP

A historical note on Wireguard VPN

Wireguard was previously recommended as an alternative to SSH port forwarding, but this type of setup is against Google policy. Wireguard should not be used.

Optional final touches

Optional: Make the drive writable

Note: This step is automatically performed for you when you deploy Chrome to your test Chromebook. However, you may need to explicitly use this step if, for example, you're debugging a crash on Chrome binary directly from Goldeneye (link), want to edit /etc/chrome_dev.conf (next bullet point) before deploying custom Chrome.

Once ssh’d in, run:

$ /usr/libexec/debugd/helpers/dev_features_rootfs_verification
$ reboot ; exit

This removes rootfs verification and makes the drive writeable. master You only need to follow this section if you wish to enable verbose logging or pass a runtime flag to Chrome. The drive must be writeable to follow this section.

/etc/chrome_dev.conf contains the runtime arguments for every time Chrome (the ui executable) is started. Whenever you change /etc/chrome_dev.conf, you’ll need to restart Chrome (in order for the arguments to take effect) via:

$ restart ui

The most common reason you’ll want to edit /etc/chrome_dev.conf is to pass the flags that enable logs. See the Logging documentation.

Optional: Ensure your firmware is up-to-date

If your device’s firmware is out of date, you may run into random reboots and other weird behavior while using it. To prevent that, ensure that your device’s firmware is updated (you need to be connected to the Internet when running this command) by running the following on the Chromebook:

$ chromeos-firmwareupdate --mode=autoupdate
$ reboot

Optional: Configure a SSH config file

To make logging into your Chromebook over ssh easier, you can specify the connection details in ~/.ssh/config (create the directory and file if it doesn't exist). For example, if you add:

Host eve
  Port 2233
  User root

Then you can use $ ssh eve instead of $ ssh -p 2233 root@

Optional: Setup SSH key authentication

All ChromeOS test images have the same SSH public key set up for authentication, so if you download the private key, save it as ~/.ssh/testing_rsa, and update the permissions (chmod 0600 ~/.ssh/testing_rsa), then you can add the following to your SSH config file to allow for passwordless authentication:

Host eve
  Port 2233
  User root
  IdentityFile %d/.ssh/testing_rsa

History References Warnings

Up next

You're now ready to download the code necessary to build and deploy ChromiumOS.

< Development environment
Checkout Chromium >