RPi Ramdisk

Builds two ramdisk environments for Raspberry Pi.

• raspbian is a full featured system based on Raspbian, including apt.

• busybox-klibc is a minimal tiny environment that is under 1MB.

The ramdisks are loaded fully into RAM at boot time, after which the SD card is not touched. This means the SD card is extremely unlikely to become corrupted. It also means any changes made on the live system are wiped after a reboot, so the ramdisk must be customized for its task during the build process.

Build Dependencies

Debian-based systems

This dependency list may be incomplete. If so, please report a bug on github.

sudo apt install libc6:i386 libstdc++6:i386 libgcc1:i386 \
                 libncurses5:i386 libtinfo5:i386 zlib1g:i386 \
                 build-essential git bc python zip wget gettext \
                 autoconf automake libtool pkg-config autopoint \
                 bison flex libglib2.0-dev gobject-introspection \
                 multistrap fakeroot fakechroot proot cpio \
                 qemu-user-static binfmt-support makedev

Some build dependencies need to be fairly new:

Git >= 2.12 is needed for "rev-parse --absolute-git-dir". It is available in Ubuntu 17.10 and newer, or from this PPA if you are on an older release:

https://launchpad.net/~git-core/+archive/ubuntu/ppa

Qemu >= 2.7 is needed for the getrandom() syscall. It is available in Ubuntu 17.10 and newer, or from the Ubuntu Cloud Archive:

https://wiki.ubuntu.com/OpenStack/CloudArchive

Submodules

This repository uses git submodules. After cloning the repository run:

git submodule update --init

To pull changes from upstream run:

git submodule update --remote

Compiling

Running make will build everything. Parallel make e.g. make -j8 is supported and will greatly decrease the kernel build times.

The submodule build output is redirected to /dev/null by default. To show it for the kernel:

make VERBOSE_KERNEL_BUILD=1

You can also substitute "KERNEL" with "QT", "GSTREAMER", "RYGEL" etc for those packages.

For faster kernel builds, ccache can be used. Install it first, then:

make USE_CCACHE=1

To speed up initrd building, you can use apt-cacher-ng. Install it, and then:

export APT_HTTP_PROXY=http://localhost:3142
make

Docker

Check the Dockerfile and build-docker scripts which automate the entire build process.

Booting

The build produces a boot directory for each environment. For example boot-raspbian/. This directory contains everything needed to boot the respective environment on any model of Raspberry Pi.

For each boot directory a boot zip is also created. For example boot-raspbian.zip. This is just a zipped version of the boot directory.

SD Card

The SD card first primary partition should be fat formatted. (This is the default for new, blank SD cards.) Copy the contents of the boot directory onto the fat partition on the SD card. Put the SD card in the Raspberry Pi and turn it on.

USB Mass Storage

USB mass storage booting must be enabled first:

https://www.raspberrypi.org/documentation/hardware/raspberrypi/bootmodes/msd.md

Then the procedure is the same as SD card booting: copy the contents of the boot directory to the mass storage device, plug it in, and turn on.

TFTP Boot

Copy bootcode.bin to the fat partition on your SD card. Edit dnsmasq.conf and change the tftpboot path to contain the absolute path to the boot directory and then run sudo dnsmasq -C dnsmasq.conf. Now put the SD card in the Pi and boot. Wired ethernet must be connected.

Note: TFTP booting is unreliable due to:

https://github.com/raspberrypi/firmware/issues/764

USB device boot

Build rpiboot from:

https://github.com/raspberrypi/usbboot

Connect a Pi Zero or similar using a USB cable. Then run:

sudo rpiboot -d boot-busybox-klibc

Note: Raspbian image is too big to boot using this method, see:

https://github.com/raspberrypi/usbboot/issues/14