Buildroot #

Buildroot can generate minimal VM image with custom kernel in multiple architectures:

Set up #

1. Download and extract.
2. Ensure the packages are installed: bc libnurses libssl-dev libelf-dev

Build for QEMU #

• Use the pre-set configuration: make qemu_x86_64_defconfig and make further changes with make menuconfig.
• In Build options, configure make parallelism.

Kernel #

• In Kernel, use custom kernel config fragment file
  • kernel configuration: use the architecture default configuration
• To build a custom kernel version, need to select the corresponding kernel header in ToolChain
• To modify kernel options: make linux-menuconfig

Rebuild #

• Clean rebuild a package: make <package>-dirclean, this will remove the package’s builddir in output/build.
  • make linux-dirclean will clean up Linux kernel.
• Re-run make & make install: make <package>-rebuild

Packages #

• In Target packages, Networking applications, check dropbear. The ssh server will be started as part of /etc/init.d/rcS.

Overlay directory tree #

Add files you want to include in the VM root file-system. To enable networking in the guest:

cat << EOF >> /etc/network/interfaces
auto eth0
iface eth0 inet dhcp
EOF

Add this file into the overlay directory.

Boot QEMU #

../tree/bin/qemu-system-x86_64 -enable-kvm \
    -kernel ../buildroot-2020.02/output/images/bzImage \
    -hda ../buildroot-2020.02/output/images/rootfs.ext4 \
    -m 1G \
    -append "root=/dev/sda rw console=ttyS0" \
    -serial stdio \
    -device virtio-rng-pci \
    -device e1000,netdev=net0 \
    -netdev user,id=net0,hostfwd=tcp::5555-:22

Reference #

• busybox & buildroot
• 6 tips