Build a basic Linux kernel and ramdisk that can start in QEMU.

docker/buildramfs.sh

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+#!/bin/bash
+ 
+ARCH="x86_64"
+BB_VER="1.31.0"
+ 
+# Dirs
+mkdir -p root
+cd root
+mkdir -p bin dev etc lib mnt proc sbin sys tmp var
+cd -
+ 
+# Utils
+if [ ! -f "root/bin/busybox" ]; then
+    curl -L "https://www.busybox.net/downloads/binaries/${BB_VER}-defconfig-multiarch-musl/busybox-${ARCH}" >root/bin/busybox
+fi
+cd root/bin
+chmod +x busybox
+ln -s busybox mount
+ln -s busybox sh
+cd -
+ 
+# Init process
+ 
+cat >>root/init << EOF
+#!/bin/busybox sh
+/bin/busybox --install -s /bin
+mount -t devtmpfs  devtmpfs  /dev
+mount -t proc      proc      /proc
+mount -t sysfs     sysfs     /sys
+mount -t tmpfs     tmpfs     /tmp
+setsid cttyhack sh
+exec /bin/sh
+EOF
+chmod +x root/init
+ 
+# initramfs creation
+ 
+cd root
+find . | cpio -ov --format=newc | gzip -9 >../initramfs
+cd -