diskimage-builder/diskimage_builder/elements/ramdisk/init.d/10-start-base-system

mkdir -p /proc /sys /dev /boot /etc /mnt /lib/modules

mount -t proc proc /proc

mount -o ro -t sysfs none /sys

UDEVD=
if [ -x "/bin/systemd-udevd" ]; then
    UDEVD="systemd-udevd"
else
    UDEVD="udevd"
fi

# udev versions 176 and newer require a different on-disk setup
UDEVD_VERSION=$(udevadm --version)

if [ "$UDEVD_VERSION" != "" -a $UDEVD_VERSION -gt 175 ]; then
    echo "Using new-style udevd setup"
    mount -t devtmpfs none /dev
    mkdir -p /run
    mount -t tmpfs -o "nosuid,size=20%,mode=0755" tmpfs /run
    mkdir -p /run/{lock,udev}
else
    echo "Using old-style udevd setup"
    mount -t tmpfs none /dev
    ln -sf /proc/self/fd /dev/fd
    mknod /dev/null c 1 3
    mknod /dev/zero c 1 5
    mknod /dev/random c 1 8
    mknod /dev/urandom c 1 9
    mknod /dev/tty0 c 4 0
    mknod /dev/tty1 c 4 1
    mknod /dev/tty2 c 4 2
    mknod /dev/tty3 c 4 3
    mknod /dev/tty4 c 4 4
    mknod /dev/tty5 c 4 5
    mknod /dev/tty6 c 4 6
    mknod /dev/tty7 c 4 7
    mknod /dev/tty8 c 4 8
    mknod /dev/tty9 c 4 9
    mknod /dev/tty c 5 0
    mknod -m 0600 /dev/console c 5 1
    mknod -m 0666 /dev/ptmx c 5 2
    mkdir -p /dev/.udev/data
fi

echo "starting syslogd"

echo '*.* /initlog' > /etc/syslog.conf
syslogd
klogd

echo "starting udevd"
$UDEVD --daemon --resolve-names=never

echo "load modules"
load_modules_by_udev