initramfs对应的init脚本文件，解压后可见

cat /proc/cmdline
BOOT_IMAGE=/boot/vmlinuz-3.13.0-44-generic root=UUID=cb57e3e8-6f60-42c1-863d-1617454d360e ro quiet splash vt.handoff=7

下面是init脚本内容，cp来源与/usr/share/initram-tools/init。

（具体见mkinitramfs脚本命令。）

#!/bin/sh

[ -d /dev ] || mkdir -m 0755 /dev
[ -d /root ] || mkdir -m 0700 /root
[ -d /sys ] || mkdir /sys
[ -d /proc ] || mkdir /proc
[ -d /tmp ] || mkdir /tmp
mkdir -p /var/lock
mount -t sysfs -o nodev,noexec,nosuid sysfs /sys
mount -t proc -o nodev,noexec,nosuid proc /proc
# Some things don't work properly without /etc/mtab.
ln -sf /proc/mounts /etc/mtab

grep -q '\<quiet\>' /proc/cmdline || echo "Loading, please wait..."

# Note that this only becomes /dev on the real filesystem if udev's scripts
# are used; which they will be, but it's worth pointing out
if ! mount -t devtmpfs -o mode=0755 udev /dev; then
    echo "W: devtmpfs not available, falling back to tmpfs for /dev"
    mount -t tmpfs -o mode=0755 udev /dev
    [ -e /dev/console ] || mknod -m 0600 /dev/console c 5 1
    [ -e /dev/null ] || mknod /dev/null c 1 3
fi
mkdir /dev/pts
mount -t devpts -o noexec,nosuid,gid=5,mode=0620 devpts /dev/pts || true
mount -t tmpfs -o "noexec,nosuid,size=10%,mode=0755" tmpfs /run
mkdir /run/initramfs
# compatibility symlink for the pre-oneiric locations
ln -s /run/initramfs /dev/.initramfs

# Export the dpkg architecture
export DPKG_ARCH=
. /conf/arch.conf

# Set modprobe env
export MODPROBE_OPTIONS="-qb"

# Export relevant variables
export ROOT=
export ROOTDELAY=
export ROOTFLAGS=
export ROOTFSTYPE=
export IP=
export BOOT=
export BOOTIF=
export UBIMTD=
export break=
export init=/sbin/init
export quiet=n
export readonly=y
export rootmnt=/root
export debug=
export panic=
export blacklist=
export resume=
export resume_offset=
export recovery=

# mdadm needs hostname to be set. This has to be done before the udev rules are called!
if [ -f "/etc/hostname" ]; then
        /bin/hostname -b -F /etc/hostname 2>&1 1>/dev/null
fi

# Bring in the main config
. /conf/initramfs.conf
for conf in conf/conf.d/*; do
    [ -f ${conf} ] && . ${conf}
done
. /scripts/functions

# Parse command line options
for x in $(cat /proc/cmdline); do
    case $x in
    init=*)
        init=${x#init=}
        ;;
    root=*)
        ROOT=${x#root=}
        case $ROOT in
        LABEL=*)
            ROOT="${ROOT#LABEL=}"

            # support any / in LABEL= path (escape to \x2f)
            case "${ROOT}" in
            */*)
            if command -v sed >/dev/null 2>&1; then
                ROOT="$(echo ${ROOT} | sed 's,/,\\x2f,g')"
            else
                if [ "${ROOT}" != "${ROOT#/}" ]; then
                    ROOT="\x2f${ROOT#/}"
                fi
                if [ "${ROOT}" != "${ROOT%/}" ]; then
                    ROOT="${ROOT%/}\x2f"
                fi
                IFS='/'
                newroot=
                for s in $ROOT; do
                    newroot="${newroot:+${newroot}\\x2f}${s}"
                done
                unset IFS
                ROOT="${newroot}"
            fi
            esac
            ROOT="/dev/disk/by-label/${ROOT}"
            ;;
        UUID=*)
            ROOT="/dev/disk/by-uuid/${ROOT#UUID=}"    #这里的by-uuid和grub里面的一样！
            ;;
        /dev/nfs)
            [ -z "${BOOT}" ] && BOOT=nfs
            ;;
        esac
        ;;
    rootflags=*)
        ROOTFLAGS="-o ${x#rootflags=}"
        ;;
    rootfstype=*)
        ROOTFSTYPE="${x#rootfstype=}"
        ;;
    rootdelay=*)
        ROOTDELAY="${x#rootdelay=}"
        case ${ROOTDELAY} in
        *[![:digit:].]*)
            ROOTDELAY=
            ;;
        esac
        ;;
    resumedelay=*)
        RESUMEDELAY="${x#resumedelay=}"
        ;;
    loop=*)
        LOOP="${x#loop=}"
        ;;
    loopflags=*)
        LOOPFLAGS="-o ${x#loopflags=}"
        ;;
    loopfstype=*)
        LOOPFSTYPE="${x#loopfstype=}"
        ;;
    cryptopts=*)
        cryptopts="${x#cryptopts=}"
        ;;
    nfsroot=*)
        NFSROOT="${x#nfsroot=}"
        ;;
    netboot=*)
        NETBOOT="${x#netboot=}"
        ;;
    ip=*)
        IP="${x#ip=}"
        ;;
    boot=*)
        BOOT=${x#boot=}
        ;;
    ubi.mtd=*)
        UBIMTD=${x#ubi.mtd=}
        ;;
    resume=*)
        RESUME="${x#resume=}"
        ;;
    resume_offset=*)
        resume_offset="${x#resume_offset=}"
        ;;
    noresume)
        noresume=y
        ;;
    panic=*)
        panic="${x#panic=}"
        case ${panic} in
        *[![:digit:].]*)
            panic=
            ;;
        esac
        ;;
    quiet)
        quiet=y
        ;;
    ro)
        readonly=y
        ;;
    rw)
        readonly=n
        ;;
    debug)
        debug=y
        quiet=n
        exec >/run/initramfs/initramfs.debug 2>&1
        set -x
        ;;
    debug=*)
        debug=y
        quiet=n
        set -x
        ;;
    break=*)
        break=${x#break=}
        ;;
    break)
        break=premount
        ;;
    blacklist=*)
        blacklist=${x#blacklist=}
        ;;
    netconsole=*)
        netconsole=${x#netconsole=}
        ;;
    BOOTIF=*)
        BOOTIF=${x#BOOTIF=}
        ;;
    hwaddr=*)
        BOOTIF=${x#BOOTIF=}
        ;;
    recovery)
        recovery=y
        ;;
    esac
done

if [ -n "${noresume}" ]; then
    export noresume
    unset resume
else
    resume=${RESUME:-}
fi

maybe_break top

# export BOOT variable value for compcache,
# so we know if we run from casper
export BOOT

# Don't do log messages here to avoid confusing graphical boots
run_scripts /scripts/init-top

maybe_break modules
[ "$quiet" != "y" ] && log_begin_msg "Loading essential drivers"
load_modules
[ "$quiet" != "y" ] && log_end_msg

[ -n "${netconsole}" ] && modprobe netconsole netconsole="${netconsole}"

maybe_break premount
[ "$quiet" != "y" ] && log_begin_msg "Running /scripts/init-premount"
run_scripts /scripts/init-premount
[ "$quiet" != "y" ] && log_end_msg

maybe_break mount
log_begin_msg "Mounting root file system"
. /scripts/${BOOT}
parse_numeric ${ROOT}
maybe_break mountroot
mountroot
log_end_msg

maybe_break bottom
[ "$quiet" != "y" ] && log_begin_msg "Running /scripts/init-bottom"
run_scripts /scripts/init-bottom
[ "$quiet" != "y" ] && log_end_msg

# Preserve information on old systems without /run on the rootfs
if [ -d ${rootmnt}/run ]; then
    mount -n -o move /run ${rootmnt}/run
else
    # The initramfs udev database must be migrated:
    if [ -d /run/udev ] && [ ! -d /dev/.udev ]; then
        mv /run/udev /dev/.udev
    fi
    # The initramfs debug info must be migrated:
    if [ -d /run/initramfs ] && [ ! -d /dev/.initramfs ]; then
        mv /run/initramfs /dev/.initramfs
    fi
    umount /run
fi

# Move virtual filesystems over to the real filesystem
mount -n -o move /sys ${rootmnt}/sys
mount -n -o move /proc ${rootmnt}/proc

validate_init() {
    checktarget="${1}"

    # Work around absolute symlinks
    if [ -d "${rootmnt}" ] && [ -h "${rootmnt}${checktarget}" ]; then
        case $(readlink "${rootmnt}${checktarget}") in /*)
            checktarget="$(chroot ${rootmnt} readlink ${checktarget})"
            ;;
        esac
    fi

    # Make sure the specified init can be executed
    if [ ! -x "${rootmnt}${checktarget}" ]; then
        return 1
    fi

    # Upstart uses /etc/init as configuration directory :-/
    if [ -d "${rootmnt}${checktarget}" ]; then
        return 1
    fi
}

# Check init bootarg
if [ -n "${init}" ]; then
    if ! validate_init "$init"; then
        echo "Target filesystem doesn't have requested ${init}."
        init=
    fi
fi

# Common case: /sbin/init is present
if [ ! -x "${rootmnt}/sbin/init" ]; then
    # ... if it's not available search for valid init
    if [ -z "${init}" ] ; then
        for inittest in /sbin/init /etc/init /bin/init /bin/sh; do
            if validate_init "${inittest}"; then
                init="$inittest"
                break
            fi
        done
    fi

    # No init on rootmount
    if ! validate_init "${init}" ; then
        panic "NNo init found. Try passing init= bootarg." #这里多了一个N，自己加的。
    fi
fi

maybe_break init

# don't leak too much of env - some init(8) don't clear it
# (keep init, rootmnt)
unset debug
unset MODPROBE_OPTIONS
unset DPKG_ARCH
unset ROOTFLAGS
unset ROOTFSTYPE
unset ROOTDELAY
unset ROOT
unset IP
unset BOOT
unset BOOTIF
unset UBIMTD
unset blacklist
unset break
unset noresume
unset panic
unset quiet
unset readonly
unset resume
unset resume_offset

# Chain to real filesystem
exec run-init ${rootmnt} ${init} "$@" ${recovery:+--startup-event=recovery} <${rootmnt}/dev/console >${rootmnt}/dev/console 2>&1
panic "Could not execute run-init."