Linux chroot 并使用之前系统设备节点

/*********************************************************************************
 *                    Linux chroot 并使用之前系统设备节点
 * 说明：
 *     直接使用chroot结果/dev下没有设备，所有有些东西需要提前挂载，在进入chroot。
 *
 *                                       2016-12-30 深圳 南山平山村 曾剑锋
 ********************************************************************************/

一、参考文档：
    . mount dev, proc, sys in a chroot environment?
        http://superuser.com/questions/165116/mount-dev-proc-sys-in-a-chroot-environment

二、主要Linux Shell命令：
    . mount /dev/mmcblk0p2 /mnt
    . mount -t proc proc /mnt/proc
    . mount -t sysfs sys /mnt/sys
    . mount -o bind /dev /mnt/dev
    . chroot /mnt/

三、实际操作及数据：
    [zengjf@root ~]#  df
    Filesystem           1K-blocks      Used Available Use% Mounted on
    /dev/root                       % /
    tmpfs                                   % /dev/shm
    tmpfs                                  % /tmp
    tmpfs                                  % /run
    [zengjf@root ~]#  mount /dev/mmcblk0p2 /mnt
    EXT3-fs: barriers not enabled
    kjournald starting.  Commit interval  seconds
    EXT3-fs (mmcblk0p2): warning: checktime reached, running e2fsck is recommended
    EXT3-fs (mmcblk0p2): using internal journal
    EXT3-fs (mmcblk0p2): recovery complete
    EXT3-fs (mmcblk0p2): mounted filesystem with writeback data mode
    [zengjf@root ~]#  mount -t proc proc /mnt/proc
    [zengjf@root ~]#  mount -t sysfs sys /mnt/sys
    [zengjf@root ~]#  mount -o bind /dev /mnt/dev
    [zengjf@root ~]#  chroot /mnt/

    BusyBox v1.20.2 () built-in shell (ash)
    Enter 'help' for a list of built-in commands.

    [zengjf@root /]#  ls /dev/
    alarm               ptyr8               tty26               ttyr1
    apm_bios            ptyr9               tty27               ttyr2
    buzzer              ptyra               tty28               ttyr3
    console             ptyrb               tty29               ttyr4
    cpu_dma_latency     ptyrc               tty3                ttyr5
    fb0                 ptyrd               tty30               ttyr6
    fb1                 ptyre               tty31               ttyr7
    fb2                 ptyrf               tty32               ttyr8
    full                ptys0               tty33               ttyr9
    galcore             ptys1               tty34               ttyra
    i2c-               ptys2               tty35               ttyrb
    i2c-               ptys3               tty36               ttyrc
    i2c-               ptys4               tty37               ttyrd
    i2c-               ptys5               tty38               ttyre
    input               ptys6               tty39               ttyrf
    kmem                ptys7               tty4                ttys0
    kmsg                ptys8               tty40               ttys1
    log                 ptys9               tty41               ttys2
    mem                 ptyt2               tty5                ttysb
    mmcblk0             ptyt3               tty50               ttysc
    mmcblk0boot0        ptyt4               tty51               ttysd
    mmcblk0boot1        ptyt5               tty52               ttyse
    mmcblk0p1           ptyt6               tty53               ttysf
    mmcblk0p2           ptyt7               tty54               ttyt0
    mx6check            ptyt8               tty55               ttyt1
    mxc_asrc            ptyt9               tty56               ttyt2
    mxc_ipu             ptyta               tty57               ttyt3
    mxc_vpu             ptytb               tty58               ttyt4
    mxs_viim            ptytc               tty59               ttyt5
    network_latency     ptytd               tty6                ttyt6
    network_throughput  ptyte               tty60               ttyt7
    null                ptytf               tty61               ttyt8
    ...
    [zengjf@root /]#  ls sys
    block     class     devices   fs        kernel    power
    bus       dev       firmware  fsl_otp   module
    [zengjf@root /]#  ls proc
                                         cpuinfo        mounts
                                        crypto         mtd
                                        devices        net
                                      diskstats      pagetypeinfo
                                      dri            partitions
                                      driver         scsi
                                      execdomains    self
                                        fb             slabinfo
                                         filesystems    softirqs
                                         fs             stat
                                       interrupts     swaps
                                       iomem          sys
                                         ioports        sysrq-trigger
                                         irq            sysvipc
                                         kallsyms       timer_list
                           apm            kmsg           tty
                             asound         kpagecount     uptime
                           buddyinfo      kpageflags     version
                           bus            loadavg        vmallocinfo
                           cmdline        locks          vmstat
                           config.gz      meminfo        zoneinfo
                             consoles       misc
                           cpu            modules
    [zengjf@root /]#  df
    Filesystem           1K-blocks      Used Available Use% Mounted on
    /dev/root                            % /
    devpts                          % /dev/pts
    tmpfs                           % /dev/shm
    tmpfs                                % /tmp
    df: /run: No such file or directory
    /dev/mmcblk0p2                       % /
    /dev/root                       % /dev
    [zengjf@root /]#  exit
    [zengjf@root ~]#  df
    Filesystem           1K-blocks      Used Available Use% Mounted on
    /dev/root                       % /
    tmpfs                                   % /dev/shm
    tmpfs                                  % /tmp
    tmpfs                                  % /run
    /dev/mmcblk0p2                       % /mnt
    /dev/root                       % /mnt/dev
    [zengjf@root ~]#