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THE GRUB SWITCH   License: MIT Maintainer email

See quickstart.pdf for the fastest way to your custom boot configuration.


(c) 2019-2023 Ruediger Willenberg

This project enables PC users to select the OS to be booted by GRUB through hardware. It has three independently usable components:

1. Configuration scripts

A suite of bash scripts in 1_config_scripts, all controlled by one easy-to-use text UI, that provide the following capabilities:

  • parse the grub.cfg file for all menu entries that represent OS boot options
  • enable the user to pick menu entries and order them with numbers (1..15)
  • generate GRUB script files that make a specific menu entry the default choice; these files can be put on separate USB flash drives; plugging one in will represent that choice of OS to be booted
  • enhance the existing grub.cfg - in a non-destructive way that survives kernel updates - to look for a boot choice script on a plugged-in drive
  • install a list of file hashes in GRUB so that only the generated files will be executed

When using several USB flash drives for the boot choices (small, old ones will do), no further hardware is necessary.

GRUB does not need to be patched, rebuilt or reinstalled. The employed extension of grub.cfg is robust against unavailable or malformed data. Any unexpected choices or scripts will be ignored. You can always get to the regular GRUB boot menu.

2. USB device firmware

The 2_usb_device directory holds firmware source code for Microchip/Atmel ATmega32U4 MCUs that can act as USB devices. It has build support and pre-built firmware images for common maker boards like Teensy 2.0, Arduino Micro, Adafruit ItsyBitsy and Sparkfun Pro Micro. Other boards with the ATmega32u4 can be easily added.

A board with the firmware installed will register as a regular USB flash drive when plugged in and provide one of the generated files for the regular flash drives; however, you can control which file (i.e. which boot choice) is picked through pins on the board.

The firmware does NOT need to be rebuilt to change the boot configuration; a new boot configuration can just be written to the USB drive. With a switch or jumper, write-protect can be activated.

Boards can be connected to common rotary, toggle or binary-encoding switches to realize boot choice.

3. Custom USB Hardware

For easier panel and case mounting (and for fun), we designed our own PCB for ATmega32U4 or ATmega16U4 chips. EAGLE and Gerber files and all other required information can be found in 3_custom_hardware. It features:

  • Solder pads for common 1-of-12-rotary encoder and on/off/on-toggle switches with front panel mounting threads; no soldering cables required.
  • Supports USB connection both by Mini-B-plug or directly by internal ribbon cable to motherboard USB pinheaders.
  • Firmware easily re-programmable by pushing a button; works with factory ATmega32U4 chips, no custom bootloader needs to be installed.
  • Switch- or jumper-controlled write-protect
  • Can be used with self-written firmware for other purposes, like any commercial board; provides up to 13 I/O-pins with 5V logic.

Obviously this requires soldering skills and is likely not the cheapest hardware option, especially because you have to order your own PCB. But it's fun!

NEW: Miscellaneous contributions

In directory 4_misc, you can find community contributions like case designs and wiring diagrams that could be helpful with GRUB Switch building, mounting, etc.


Many thanks to Seriosha Remmlinger, Volker Wunsch and Andreas Flachsbarth for helpful feedback and suggestions and to Christoph Dehmer for examining an alternative approach (GRUB menu control by USB HID keyboard).

Thank you to Pina Merkert from Germany's biggest computer magazine c't for helping me write and publish an article about this, and for her cool contributions in 4_misc.

Stephen Holdaway has a very cool Hackaday project doing something similar with an STM32 controller. He's built a very neat way to define the FAT file structure in his C code.

We are grateful to for providing our firmware with a unique USB ID (VID 1209 / PID 2015).

Thank you to the GNU GRUB developers and maintainers for all their hard work.

See quickstart.pdf for the fastest way to your custom boot configuration.

The documentation directory holds more detailed information.

Send any questions or suggestions to Please be patient. I have a life.


Linux configuration scripts and ATmega32u4-based USB device to control GRUB boot choice through hardware







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