Overview
gokrazy packs your Go application(s) into an SD card image for the
Raspberry Pi 3 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.
Then, use the go tool to download and install gokr-packer:
go get -u github.com/gokrazy/tools/cmd/gokr-packer
Overwriting an SD card for the Raspberry Pi 3
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 and power it up! Once
the Raspberry Pi 3 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…
-
…packed the latest firmware
and kernel binaries into the
boot file system. -
…built the specified Go packages using
go installand packed all
their binaries into the/userdirectory of the root file system. -
…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
To update your gokrazy installation (running on a Raspberry Pi 3),
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), FAT16B (but see issue #10)
3, 500 MB, root3 (gokrazy+apps), FAT16B (but see issue #10)
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 firmware files
- github.com/gokrazy/kernel: pre-built kernel image and bootloader config