安全弹出 USB live 系统，要求 uesr 将其删除

Question

为了我的工作，我正在使用 Clonezilla 准备一个实时 USB。它运行自定义 bash 脚本来克隆磁盘。该 USB 将被克隆到其他几个 USB，以便它们可以在多台机器上使用。

由于要克隆的映像 (22G) 位于 USB 中，因此无法在 RAM 中运行 Clonezilla。

我想在我的脚本中复制实时 Linux 发行版安装程序的标准行为，即要求移除 USB 介质，然后按 Enter 键重新启动计算机。

使用的示例脚本eject，但这似乎不正确：

eject /dev/sdb
read -r -p 'Remove USB and press Enter' # not executed since the USB is no longer plugged
reboot

我想成为非常确保安全地移除 USB，因为它们是工作时使用的，而且数量很多，当然不能冒损坏它们的风险。

最好和最安全的方法是什么？

现在，为什么要为了一件看似微不足道的事情付出如此大的努力呢？ USB 将部署到数百台机器上。所有可以自动化的事情都需要赢得时间并避免错误。用户需要检查克隆是否有效，然后重新启动。但如果 USB 仍然插入，机器将启动它而不是本地操作系统。

这个问题是相关的但我知道它不适用于实时系统。

---

这是一个似乎可以做到这一点的脚本，来自我filesystem.squashfs从 ISO 中解压缩文件的 Lubuntu。我仍在尝试理解它，感谢任何帮助。

#! /bin/sh

# Author: Mathieu Trudel-Lapierre <[email protected]>
#         Tollef Fog Heen <[email protected]>
#         Marco Amadori <[email protected]>
#

PATH=/usr/sbin:/usr/bin:/sbin:/bin
NAME=casper
SCRIPTNAME=/etc/init.d/${NAME}
DO_SNAPSHOT=/sbin/${NAME}-snapshot

# Exit if system was not booted by casper
[ -f /run/.casper-boot ] || exit 0

# Exit if the system was booted from an ISO image rather than a physical CD
grep -qs find_iso= /proc/cmdline && exit 0

# Read configuration variable file if it is present
[ -r /etc/$NAME.conf ] && . /etc/$NAME.conf

# Try to cache everything we're likely to need after ejecting.  This
# is fragile and simple-minded, but our options are limited.
cache_path() {
    path="$1"

    if [ -d "$path" ]; then
        for f in $(find "$path" -type f); do
            cache_path "$f"
        done
    elif [ -f "$path" ] && [ ! -L "$path" ]; then
        if [ -x "$path" ]; then
            if file -L "$path" | grep -q 'dynamically linked'; then
                for lib in $(ldd "$path" | awk '{ print $3 }'); do
                    cache_path "$lib"
                done
            fi
        fi
        echo -n >> "$path"
    fi
}

do_stop ()
{
    logger -t ${NAME} "resyncing snapshots and caching reboot files..."

    if [ ! -z "${ROOTSNAP}" ]; then
        $DO_SNAPSHOT --resync-string="${ROOTSNAP}"
    fi

    if [ ! -z "${HOMESNAP}" ]; then
        $DO_SNAPSHOT --resync-string="${HOMESNAP}"
    fi

    # check for netboot
    if [ ! -z "${NETBOOT}" ] || grep -qs netboot /proc/cmdline || grep -qsi root=/dev/nfs /proc/cmdline  || grep -qsi root=/dev/cifs /proc/cmdline ; then
        return 0
    fi

    # Don't prompt to eject the SD card on Babbage board, where we reuse it
    # as a quasi-boot-floppy. Technically this uses a bit of ubiquity
    # (archdetect), but since this is mostly only relevant for
    # installations, who cares ...
    if type archdetect >/dev/null 2>&1; then
        subarch="$(archdetect)"
        case $subarch in
            arm*/imx51)
                return 0
                ;;
        esac
    fi

    prompt=1
    if grep -qs noprompt /proc/cmdline || [ -e /run/casper-no-prompt ]; then
        prompt=
    fi

    for path in $(which halt) $(which reboot) /bin/chvt /etc/rc?.d /etc/default $(which stty) /bin/plymouth /lib/plymouth /lib/*/plymouth /lib/systemd /etc/systemd /lib/*/libnss_files* /etc/nsswitch.conf /usr/share/fonts/truetype/dejavu/DejaVuSans.ttf /usr/share/fonts/truetype/ubuntu/Ubuntu-R.ttf /usr/share/fonts/truetype/ubuntu/UbuntuMono-R.ttf /etc/fonts/fonts.conf /etc/fonts/conf.d/60-latin.conf; do
        cache_path "$path"
    done

    device="$(grep " /cdrom " /proc/mounts | cut -d' ' -f1)" || device=
    # If /cdrom isn't mounted, don't try to eject it
    if [ -z "$device" ]; then
        return 0
    fi

    # If the device exists but can't be found in /sys/block, it's most likely a partition
    # so unmount it (lazy mode) and sync
    if [ -b "$device" ] && [ ! -f "/sys/block/$(basename $device)/removable" ]; then
        umount -l $device >/dev/null 2>&1
        sync
        # from now on operate on the partition's block device
        device=/dev/$(basename "$(readlink -f /sys/class/block/$(basename $device)/..)")
    fi

    # If we're still there, then we're probably a cdrom or other media
    # ship the eject if the kernel says the media isn't removable
    if [ "$(cat /sys/block/$(basename $device)/removable)" = "0" ]; then
        return 0
    fi

    # XXX - i18n
    MSG="Please remove the installation medium, then press ENTER: "
    MSG_FALLBACK="Please remove the installation medium, then reboot."

    if [ "$prompt" ]; then
        if [ -x /bin/plymouth ] && plymouth --ping; then
            chvt 63
            plymouth message --text="$MSG"
            clear > /dev/tty1
            echo $MSG_FALLBACK > /dev/tty1
        else
            stty sane < /dev/console
            echo $MSG > /dev/console
        fi
    fi

    eject -p -m $device >/dev/null 2>&1

    [ "$prompt" ] || return 0

    if [ -x /bin/plymouth ] && plymouth --ping; then
        plymouth watch-keystroke > /dev/null
    else
        read x < /dev/console
    fi
}

do_stop