##Build Linux and BusyBox 
> Environment:RedHat Enterprise Linux 10.2
> Installed:make gcc g++ ncurses-devel syslinux bison flex elfutils-libelf-devel glibc-static(Need enable codeReady repos 'sudo subscription-manager repos --enable codeready-builder-for-rhel-10-x86_64-rpms')

1.Download Kernel SRC and unzip

>tar xvf linux-x.xx.xx.tar.xz

2.make default  configuration
> make x86_64_defconfig
3.Make Kernel
> make -j8 (Compile using 8 threads)
(The bzImage is located in arch/x86_64/boot)
4.Download Busybox SRC and unzip
> tar -xjf busybox-x.xx.x.tar.bz2 
5.Modify the configuration
> make defconfig
> make menuconfig
    [Settings/Build Options]
    Enable Build static binary(no shared libs)
    [Networking Utilities/]
    Disable tc
6.Make Busybox
> make -j8
7.Create an independent root file system
>mkdir -p ~/linux-rootfs
>cd ~/linux-rootfs
>mkdir -p bin sbin usr/bin usr/sbin
>mkdir -p dev proc sys run tmp
>mkdir -p etc/init.d
>mkdir -p root home mnt
>mkdir -p var/log
>make CONFIG_PREFIX=$HOME/linux-rootfs install (In the busybox directory!)
>cd ~/linux-rootfs
>sudo mknod -m 600 dev/console c 5 1
>sudo mknod -m 666 dev/null c 1 3
>sudo mknod -m 666 dev/zero c 1 5
>sudo mknod -m 666 dev/tty c 5 0
>cat > etc/inittab <<'EOF'
     ::sysinit:/etc/init.d/rcS
     ::respawn:-/bin/sh
     ::ctrlaltdel:/sbin/reboot
     ::shutdown:/bin/umount -a -r
     EOF
>cat > etc/init.d/rcS <<'EOF'
    #!/bin/sh

    mount -t devtmpfs devtmpfs /dev
    mount -t proc proc /proc
    mount -t sysfs sysfs /sys

    mkdir -p /run /tmp
    mount -t tmpfs tmpfs /run
    mount -t tmpfs tmpfs /tmp

    echo Hi Linux.
EOF
>chmod +x etc/init.d/rcS
Check List:
    >cd ~/linux-rootfs
    >ls -l bin/busybox
    >ls -l bin/sh
    >ls -l sbin/init 
    *If /sbin/init does not exist, create it manually.->'sudo ln -sf ../bin/busybox sbin/init'
>cd ~/linux-rootfs
>sudo chown -R root:root .
>sudo ln -sf bin/busybox init
>find . -print0 | sudo cpio --null -o --format=newc | gzip -9 > ~/initramfs.cpio.gz
8.Test via QEMU
qemu-system-x86_64 \
  -machine pc \
  -accel tcg \
  -cpu max \
  -m 1024 \
  -smp 1 \
  -kernel bzImage \
  -initrd initramfs.cpio.gz \
  -append "console=ttyS0 rdinit=/init" \
  -nographic \
  -no-reboot