How to debug a Kiosk Chrome application running on a Chromebox?

If you run Chrome with the --remote-debugging-port=9222 option it will provide access to DevTools at http://localhost:9222/. Now, on a Chromebox running in Kiosk mode that's not all that useful (or even possible) without some extra steps:

1. Put your device in "developer mode". Instructions vary depending on hardware model.
2. Make the file system writable so that you can modify chrome's command line arguments.
3. Add "--remote-debugging-port=9222" to /etc/chrome_dev.conf.
4. killall chrome or pkill chrome so that the command line changes take effect.
5. Use ssh to log into the Chromebox and forward the port locally: ssh -L9222:127.0.0.1:9222 chronos@<chromebox ip>
6. Access DevTools from your local machine at http://localhost:9222/

Given all this it is easier to debug a kiosk app if you can run it unpackaged in non-kiosk mode.

In the hopes of saving other a bit of time in the future, I found that you do not need to ssh in as the chronos user when attempting to debug an app that is running in kiosk mode.

In fact, I found that I was unable to ssh in as the chronos user while the device was running an app in unmanaged kiosk mode at all, however, I could while logged in to the OS.

Instead I had to ssh in as the root user. I was then able to setup the tunnel as documented by Reilly Grant and connect to the remote debugger via localhost:9222.

This means that the only change you need to make to Reilly Grant's instructions are in Step 5 change ssh -L9222:127.0.0.1:9222 chronos@<chromebox ip> to ssh -L9222:127.0.0.1:9222 root@<chromebox ip>