Overview

gokrazy packs your Go application(s) into an SD card image for the Raspberry Pi 3 or 4 which — aside from the Linux kernel and proprietary Raspberry Pi bootloader — only contains Go software.

The motivation is that @stapelberg spends way more time on C software and their various issues than he would like. Hence, he is going Go-only where feasible.

Usage

Installation

Install the latest Go version if you haven’t already.

Create a directory for this gokrazy instance and initialize a Go module:

INSTANCE=gokrazy/hello
mkdir -p ~/${INSTANCE?}
cd ~/${INSTANCE?}
go mod init hello

Then, install gokr-packer:

go get github.com/gokrazy/tools/cmd/gokr-packer@latest

Overwriting an SD card for the Raspberry Pi 3 or 4

To re-partition and overwrite the SD card /dev/sdx, use:

gokr-packer -overwrite=/dev/sdx github.com/gokrazy/hello

Then, put the SD card into your Raspberry Pi 3 or 4 and power it up! Once the Raspberry Pi 3 or 4 has booted (takes about 10 seconds), you should be able to reach the gokrazy web interface at the URL which gokr-packer printed.

Under the hood, gokr-packer…

1. …packed the latest firmware and kernel binaries into the boot file system.

2. …built the specified Go packages using go install and packed all their binaries into the /user directory of the root file system.

3. …created a minimal gokrazy init program which supervises all binaries (i.e. restarts them when they exit).

Updating your installation

To update gokrazy, including the firmware and kernel binaries, use:

go get -u github.com/gokrazy/tools/cmd/gokr-packer
go get -u github.com/gokrazy/gokrazy
go get -u github.com/gokrazy/kernel
go get -u github.com/gokrazy/firmware
go get -u github.com/gokrazy/rpi-eeprom

To update your gokrazy installation (running on a Raspberry Pi 3 or 4), use:

GOKRAZY_UPDATE=http://gokrazy:mysecretpassword@gokrazy/ gokr-packer github.com/gokrazy/hello

SD card contents

gokrazy uses the following partition table:

num	size	purpose	file system
1	100 MB	boot (kernel+firmware)	FAT16B
2	500 MB	root2 (gokrazy+apps)	SquashFS
3	500 MB	root3 (gokrazy+apps)	SquashFS
4	rest	permanent data	ext4

The two root partitions are used alternatingly (to avoid modifying the currently active file system) when updating.

If you’d like to store permanent data (i.e. data which will not be overwritten on the next update), you’ll need to create an ext4 file system on the last partition. If your SD card is /dev/sdx, use mkfs.ext4 /dev/sdx4.

Customization

Changing program behavior for gokrazy

gokr-packer sets the “gokrazy” build tag for conditional compilation.

You can find an example commit which implements a gokrazy-specific controller that triggers the main program logic every weekday at 10:00 at https://github.com/stapelberg/zkj-nas-tools/commit/6f90ace35981f78dcd66d611269f17f37ce4b4ef

Changing init behavior

Assuming the application you’d like to create on gokrazy lives in the repository github.com/stapelberg/mediaserver, this is how you can make gokrazy dump the generated init package’s source:

mkdir -p $(go env GOPATH)/src/github.com/stapelberg/mediaserver/cmd/init
gokr-packer \
  -overwrite_init=$(go env GOPATH)/src/github.com/stapelberg/mediaserver/cmd/init/init.go \
  github.com/gokrazy/hello

(Note that the package must result in a binary called “init”.)

Then, edit the github.com/stapelberg/mediaserver package to your liking. When done, pack an image with your own init package:

gokr-packer \
  -init_pkg=github.com/stapelberg/mediaserver/cmd/init \
  -overwrite=/dev/sdx \
  github.com/gokrazy/hello

Repository structure

• github.com/gokrazy/gokrazy: system code, main issue tracker, documentation
• github.com/gokrazy/tools: SD card image creation code, pulling in:
  • github.com/gokrazy/firmware: Raspberry Pi 3 or 4 firmware files
  • github.com/gokrazy/rpi-eeprom: Raspberry Pi 4 EEPROM files
  • github.com/gokrazy/kernel: pre-built kernel image and bootloader config