I have a Lenovo Chromebook C330, and I managed to get it to developer mode. The C330 has an ARM CPU, so I have an Ubuntu ISO from this ubuntu site (second link) on a USB drive.
When I restart the computer, it opens to the screen that reads “OS verification is off”. I have my USB drive plugged in (I know the USB drive and port work), and I press ctrl+u. The screen flashes black, then returns, making a loud angry beeping noise.
I’ve tried all sorts of things, but I seem to have reached a dead end. Any suggestions would be greatly appreciated.
First of all, good luck. I sympathize with your plight deeply. The first chromebook I tried to turn into an ultrabook was an ARM CPU and it was a nightmare that I gave up on. There’s barely any support for it in this community because it’s a pain and your paths forward are limited.
Second of all, the first thing you’ll want to fix about what you’re doing is to take that .iso off the drive as well as any files you care about. An iso alone will not do, you need to use Rufus or a similar bootable drive creator to turn that iso file and your drive into a bootable drive. This process will erase and destroy everything on the drive, so be careful.
Thirdly, ChromeOS is a pain in the behind. Evem though it says “OS Verification is Off” there is no easily accessible “boot menu” unless you can run MrChromebox’s Firmware Utility Script to get one (which you can’t, I’m afraid, since it’s an ARM CPU). Essentially, you need to flash your firmware with something that can allow you to boot Linux (RW_LEGACY or some kind of UEFI). You will also have to disable write protection which, depending on your board, could be anything from unplugging the battery to removing a WP screw to any number of steps.
Lastly, my advice to you moving forward is to get your boardname first and foremost. Then, look for options available for that board. I can tell you that Arch Linux and its associated docs/community tends to be your best bet for ARM devices but don’t expect a miracle. Crostini and crouton are also potentially options that might work for you. Just search around and see what information is available for your board because what you can do with a chromebook is very dependent on what board you have. Also, when asking for support let people know your boardname as that will give them a better idea of how they can help you.
I hope this helps and good luck. I know how disappointed I was when I realized putting Linux on my chromebook was a near impossibility. Hopefully your struggle is less difficult.