I am the proud owner of two Chromebooks – one Samsung Series 3 ARM Chromebook and one Samsung 550 Chromebook. Like many serial tinkerers the frowny/sick developer “warning” screen, which you get if you want to overwrite the operating system having to enable developer mode, is more of a pain than anything, much as I recognise it is for security. Having to press CTRL + D at every boot, or wait 30 seconds and endure a loud, audible beep is not my idea of slick fun. Happily, it is possible to all but disable this screen, by rewriting the BIOS with the correct “flags”. This leaves the screen enabled, but it only displays for 2 seconds, and there is no beep. Unhappily, you have to physically open the Chromebook up and disable the inbuilt BIOS write protect to take advantage of this.
The procedure is a follows:
- Open Chromebook and enable/disable write protect jumper
- Read existing BIOS using flashrom
- Write new BIOS file with correct flags using gbb_utility
- Write new BIOS file to BIOS using flashrom
Before proceeding, be warned that you could brick your Chromebook if you do something wrong. This is not for the faint-hearted. Do not come running/crying to me if it doesn’t work, and you are left with a tasteful paperweight!
Having said that, even if you do brick the device it is possible to rewrite a known, good BIOS using a Bus Pirate to get your Chromebook running again. I have mine ordered after bricking my Samsung 550 trying to enable VMX (hardware virtualisation extensions). When it arrives I shall write a post dedicated to that.
- Open Chromebook and enable/disable write protect jumper
The Developer Information for Chrome OS devices page has a separate page dedicated to each device. Disassembly generally involves removing screws from the bottom of the device (including under the rubber feet), and carefully wiggling and prizing apart the case.
On the Series 3 ARM Chromebook the jumper is a sticker and screw next to the USB 3.0 port (denoted by blue plastic). You have to remove both the sticker AND the screw to disable the BIOS write protect (the latter of which caught me out, as I decided to put the non rubber foot screws back in before writing the BIOS and then was frustrated to find I couldn’t actually write the BIOS).
On the Samsung 550 Chromebook the jumper is a small white affair that you have to short yourself, somehow. After some experimentation I used a small watch screwdriver (the same one I used to get the case off) gently wedged in between the pins to have the desired effect, carefully turning the Chromebook over with the screwdriver in place.
In both cases you need to “cut” the battery. This is done by removing the power then putting a paper clip into the hole directly beneath the track pad for a few seconds. Otherwise the Chromebook will not know the BIOS write-protect has been disabled. Then, of course, plug the power back in before you do anything BIOS related.
- Read existing BIOS using flashrom
This is possibly the easiest step of the entire process. Firstly log into Chrome OS (if you aren’t in Chrome OS, but already have an alternate OS installed you can build a Chromium OS image on another machine and chroot into that over a filesystem mounted via SSH and the network, or you can be old fashioned and just write it to a USB stick ;)
Then, open a terminal (CTRL-ALT-T), type “shell”, and then “sudo -s”, then navigate to your Downloads directory (just somewhere handy which is read/write to save the file to) “cd /home/user/*/Downloads”. Then type “flashrom -r bios.bin” which will read the existing BIOS and write it to the Downloads directory. That’s that part done.
You should get a message similar to:
- Write new BIOS file with correct flags using gbb_utility
Next we will use the gbb_utility to write a new BIOS file containing the flag we want to neuter the Developer mode screen “gbb_utility –set –flags=0x01 bios.bin bios.new”:
- Write new BIOS file to BIOS using flashrom
To write the file to the BIOS we use “flashrom” again – “flashrom -w bios.new”, make sure you have the sticker and screw removed, or the jumper suitably shorted as previously discussed:
Congratulations you should now have a developer mode screen which flashes by in 2 seconds and doesn’t beep!
Originally written by John Lewis. Slight changes were made to the article for layout and readability.
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