Thursday, February 12, 2009



      # Don't shut the network down if root is on NFS or a network
    # block device.
        rootfs=$(awk '{ if ($1 !~ /^[ \t]*#/ && $2 == "/") { print $3; }}' /etc/mtab)
        rootopts=$(awk '{ if ($1 !~ /^[ \t]*#/ && $2 == "/") { print $4; }}' /etc/mtab)
    if [[ "$rootfs" =~ ^nfs ]] || [[ "$rootopts" =~ "_netdev|_rnetdev" ]] ; then
        exit 1

关于/etc/mtab 的作用,可以看busybox关于mount命令是否支持/etc/mtab这个配置选项的描述:
    bool "Support for the old /etc/mtab file"
    default n
    depends on MOUNT || UMOUNT
      Historically, Unix systems kept track of the currently mounted
      partitions in the file "/etc/mtab". These days, the kernel exports
      the list of currently mounted partitions in "/proc/mounts", rendering
      the old mtab file obsolete. (In modern systems, /etc/mtab should be
      a symlink to /proc/mounts.)

      The only reason to have mount maintain an /etc/mtab file itself is if
      your stripped-down embedded system does not have a /proc directory.
      If you must use this, keep in mind it's inherently brittle (for
      example a mount under chroot won't update it), can't handle modern
      features like separate per-process filesystem namespaces, requires
      that your /etc directory be writeable, tends to get easily confused
      by --bind or --move mounts, won't update if you rename a directory
      that contains a mount point, and so on. (In brief: avoid.)

      About the only reason to use this is if you've removed /proc from
      your kernel.


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