Linux + BusyBox + QEMU/VirtualBox/USB boot recipe

.gitignore

output/

README.md

Running

$ make
$ qemu-system-x86_64 -kernel output/kernel-image -initrd output/initramfs.cpio.gz -append "root=/dev/ram0 rootfstype=ramfs init=/init console=ttyS0" -nographic -net nic,model=rtl8139 -net user

Dockerfile

################################################################################
# Base image

# We use Alpine as it is small and its toolchain is already musl-based.
FROM alpine:3.7

################################################################################
# Pulling down sources

# Get git for pulling down the kernel and busybox:
RUN apk add --update git

# Download and extract the Linux source:
RUN git clone git://github.com/torvalds/linux.git --depth 1 --branch v4.15 -q

# Download and extract BusyBox:
RUN git clone git://git.busybox.net/busybox --depth 1 --branch 1_28_1 -q

################################################################################
# Building

# Essential things for building Linux
RUN apk add bc build-base linux-headers

# Build BusyBox
RUN cd /busybox \
    && make defconfig > /dev/null \
    && make clean > /dev/null \
    && make LDFLAGS=-static install > /dev/null

# Build Linux
COPY Linuxfile /linux/config-overrides
RUN cd /linux \
    && make allnoconfig > /dev/null \
    && cat config-overrides >> .config \
    && make oldconfig > /dev/null \
    && make -j 4 \
    && mv arch/x86/boot/bzImage /bzImage

################################################################################
# File system

# Essential things for building the initramfs
RUN apk add cpio bash

# Create our initial file system
RUN mkdir /initramfs \
    && cd /initramfs \
    && bash -c 'mkdir -pv {bin,sbin,etc,proc,sys,usr/{bin,sbin,lib},lib,dev,mnt,root,tmp,var/log}' \
    && cp -av /busybox/_install/* .
COPY Initfile /initramfs/init
RUN echo nameserver 8.8.8.8 > /initramfs/etc/resolv.conf \
    && chmod 755 /initramfs/init && chmod +x /initramfs/init

################################################################################
# Final output

# Make the initramfs
RUN cd /initramfs \
    && find . -print0 \
    | cpio --null -ov --format=newc \
    | gzip -9 > /initramfs.cpio.gz

# Export the image and filesystem ready to boot into
RUN mkdir /output \
    && cp /bzImage /output/kernel-image \
    && mv /initramfs.cpio.gz /output/

# Essentials for building the ISO file
RUN apk add syslinux xorriso

# Make the boot directory
RUN mkdir -p /iso/boot; \
    cp /bzImage /iso/boot/vmlinuz64; \
    cp /output/initramfs.cpio.gz /iso/boot/initrd.img

# Make the isolinux directory
RUN mkdir -p /iso/isolinux; \
    cp /usr/share/syslinux/*.* /iso/isolinux
COPY isolinux.cfg /iso/isolinux/isolinux.cfg

# Make the ISO
RUN xorriso -as mkisofs -l -r -J -V "CUSTOM_LINUX" \
    -b isolinux/isolinux.bin \
    -isohybrid-mbr /usr/share/syslinux/isohdpfx.bin \
    -no-emul-boot \
    -boot-load-size 4 \
    -boot-info-table \
    -c isolinux/boot.cat  \
    -o /output/custom-linux.iso \
    /iso/

Initfile

#!/bin/sh

mount -t devtmpfs devtmpfs /dev
mount -t proc     none     /proc
mount -t sysfs    none     /sys

mkdir -p /var/run/
mkdir -p /etc/network/if-down.d
mkdir -p /etc/network/if-post-down.d
mkdir -p /etc/network/if-post-up.d
mkdir -p /etc/network/if-pre-down.d
mkdir -p /etc/network/if-pre-up.d
mkdir -p /etc/network/if-up.d

/sbin/mdev -s
/sbin/ifconfig lo 127.0.0.1 netmask 255.0.0.0 up
/sbin/ifconfig eth0 up 10.0.2.15 netmask 255.255.255.0 up
/sbin/route add default gw 10.0.2.2

echo -e "\nBoot took $(cut -d' ' -f1 /proc/uptime) seconds\n"

echo '<LSPCI>'
lspci -k
echo '</LSPCI>'

/usr/bin/setsid /bin/cttyhack /bin/sh
exec /bin/sh

isolinux.cfg

serial 0 9600
default linux
label linux
	kernel /boot/vmlinuz64 com1=9600,8n1
	initrd /boot/initrd.img
	append console=ttyS0 console=tty0

# see http://www.syslinux.org/wiki/index.php/SYSLINUX

# If flag_val is 0, do not load a kernel image unless it has been explicitly named in a LABEL statement. The default is 1.
implicit 0

# If flag_val is 0, display the boot: prompt only if the Shift or Alt key is pressed, or Caps Lock or Scroll lock is set (this is the default). If flag_val is 1, always display the boot: prompt.
prompt 0

# Indicates how long to pause at the boot: prompt until booting automatically, in units of 1/10 s. The timeout is cancelled when any key is pressed, the assumption being the user will complete the command line. A timeout of zero will disable the timeout completely. The default is 0.
timeout 0

Linuxfile

CONFIG_64BIT=y
CONFIG_EMBEDDED=n
CONFIG_PRINTK=y
CONFIG_PCI_QUIRKS=y
CONFIG_BLK_DEV=y
CONFIG_BLK_DEV_INITRD=y
CONFIG_INITRAMFS_SOURCE=/initramfs.cpio
CONFIG_BLOCK=y
CONFIG_SMP=y
CONFIG_PCI=y
CONFIG_MTTR=y
CONFIG_BINFMT_ELF=y
CONFIG_BINFMT_SCRIPT=y
CONFIG_EXT2_FS=y
CONFIG_INOTIFY_USER=y
CONFIG_NET=y
CONFIG_PACKET=y
CONFIG_UNIX=y
CONFIG_INET=y
CONFIG_WIRELESS=n
CONFIG_ATA=y
CONFIG_NETDEVICES=y
CONFIG_WLAN=n
CONFIG_DEVKMEM=y
CONFIG_TTY=y
CONFIG_TTY_PRINTK=y
CONFIG_SERIAL_8250=y
CONFIG_SERIAL_8250_CONSOLE=y
CONFIG_PROC_FS=y
CONFIG_PROC_KCORE=y
CONFIG_SYSFS=y
CONFIG_X86_VERBOSE_BOOTUP=y
CONFIG_EARLY_PRINTK=y
CONFIG_DEVTMPFS=y
CONFIG_DEVTMPFS_MOUNT=y
CONFIG_POSIX_TIMERS=y

################################################################################
## Networking

# For QEMU

CONFIG_NET_VENDOR_REALTEK=y
CONFIG_8139TOO=y
CONFIG_8139CP=y

# For VirtualBox

CONFIG_NET_VENDOR_INTEL=y
CONFIG_E1000=y

################################################################################
## Graphics

CONFIG_EPOLL=y # Needed for Xorg.
CONFIG_AGP=y
CONFIG_DRM_KMS_HELPER=y

# MacBook

CONFIG_DRM=y
CONFIG_DRM_FBDEV_EMULATION=y
CONFIG_DRM_I915=y
CONFIG_DRM_I915_KMS=y
CONIFG_LOGO=y
CONFIG_INTEL=y

# QEMU & VirtualBox

CONFIG_FB=y
CONFIG_DRM_BOCHS=y
CONFIG_DRM_CIRRUS_QEMU=y

# VirtualBox

CONFIG_STAGING=y
CONFIG_X86=y
CONFIG_DRM_VBOXVIDEO=y
CONFIG_DRM_TTM=y # it's not this
CONFIG_GENERIC_ALLOCATOR=y # it's not this

################################################################################
## Input devices

CONFIG_INPUT=y
CONFIG_INPUT_EVDEV=y
CONFIG_INPUT_MOUSEDEV=y