Source: Moeomu’s Blog

Prepare the environment

• Ubuntu 20.04 LTS
• Linux 4.9.229
• Busybox 1.33.0
• qemu

Download kernel source code and file system source code

• Download linux-4.9.229.tar.gz at the site Kernel.org.
• Download busybox-1.33.0.tar.bz2 from the site Busybox.net.
• Install qemu via apt: sudo apt install qemu-system-x86.

Compilation

Compiling the kernel

• export ARCH=x86。
• make x86_64_defconfig。
• make menuconfig。
  • Check General Settings -> Initial RAM file system and RAM disk (initramfs/initrd) support.
  • Check Device Driver -> Block Devices -> RAM Block Device Support.
  • Modify Device Driver -> Block Devices -> RAM Block Device Support -> (65536) default RAM disk size (kbytes).

If this step reports a fatal error: curses.h, then install sudo apt install libncurses5-dev.

• The compiled kernel is placed in the

• The compiled kernel is placed in the directory arch/x86/boot under the file name bzImage.

Compile busybox

• Compile busybox
  • Check “Settings -> Build Options -> [*] Build Busybox as a static binary (no fragmented libraries)”.
• make && make install。

Packaged file system

• mkdir etc dev mnt。

• mkdir -p proc sys tmp。

• mkdir -p etc/init.d。

• vim etc/fstab。

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  proc /proc proc defaults 0 0 tmpfs /tmp tmpfs defaults 0 0 sysfs /sys sysfs defaults 0 0

• vim etc/init.d/rcS

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  echo -e "Welcome to Moeomu Linux" /bin/mount -a echo -e "Remounting the root filesystem" mount -o remount rw / mkdir -p /dev/pts moutn -t devpts devpts /dev/pts echo /sbin/mdev > /proc/sys/kernel/hotplug mdev -s

• chmod 755 etc/init.d/rcS

• vim etc/inittab

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  ::sysinit:/etc/init.d/rcS ::respawn:-/bin/sh ::askfirst:-/bin/sh ::cttlaltdel:/bin/umount -a -r

• chmod 755 etc/inittab

• cd dev

• sudo mknod console c 5 1

• sudo mknod null c 1 3

• sudo mknod tty1 c 4 1

• The following code is executed line by line in the busybox source code directory

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  #!/bin/bash rm -rf rootfs.ext3 sudo rm -rf fs dd if=/dev/zero of=./rootfs.ext3 bs=1M count=32 mkfs.ext3 rootfs.ext3 mkdir fs sudo mount -o loop rootfs.ext3 ./fs sudo cp -rf ./_install/* ./fs sudo umount ./fs gzip --best -c rootfs.ext3 > rootfs.img.gz

• The final filesystem is generated: rootfs.img.gz

Running the system with QEMU

• qemu-system-x86_64 -kernel ./linux-4.9.229/arch/x86_64/boot/bzImage -initrd ./busybox-1.33.1/rootfs.img.gz -append "root=/dev/ram init=/linuxrc" -serial file:output.txt

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