NFS挂载网络文件系统

1.首先将电脑本地ip、ubuntu虚拟系统ip、开发板的ip地址设在同一网段，通过路由器连接开发板和电脑，然后互ping确保三者互联。
2.重新启动开发板进入boot菜单，按q退出菜单，输入print命令可以看到打印信息：

其中：

bootargs=noinitrd root=/dev/mtdblock3 init=/linuxrc console=ttySAC0

表示文件系统的启动位置，在后面步骤中将其换成在网络中虚拟ubuntu上的文件系统即可。
3.在命令行设置ipaddr和serverip

set ipaddr 202.204.53.71

set serverip 202.204.53.70

然后用save命令保存。

4.linux-2.6.22.6\Documentation\nfsroot.txt文件中的指示设置网络文件系统位置如何进行设置：

When the kernel has been loaded by a boot loader (see below) it needs to be
told what root fs device to use. And in the case of nfsroot, where to find
both the server and the name of the directory on the server to mount as root.
This can be established using the following kernel command line parameters:


root=/dev/nfs

  This is necessary to enable the pseudo-NFS-device. Note that it's not a
  real device but just a synonym to tell the kernel to use NFS instead of
  a real device.


nfsroot=[<server-ip>:]<root-dir>[,<nfs-options>]

  If the `nfsroot' parameter is NOT given on the command line,
  the default "/tftpboot/%s" will be used.

  <server-ip>   Specifies the IP address of the NFS server.
        The default address is determined by the `ip' parameter
        (see below). This parameter allows the use of different
        servers for IP autoconfiguration and NFS.

  <root-dir>    Name of the directory on the server to mount as root.
        If there is a "%s" token in the string, it will be
        replaced by the ASCII-representation of the client's
        IP address.

  <nfs-options> Standard NFS options. All options are separated by commas.
        The following defaults are used:
            port        = as given by server portmap daemon
            rsize       = 4096
            wsize       = 4096
            timeo       = 7
            retrans     = 3
            acregmin    = 3
            acregmax    = 60
            acdirmin    = 30
            acdirmax    = 60
            flags       = hard, nointr, noposix, cto, ac


ip=<client-ip>:<server-ip>:<gw-ip>:<netmask>:<hostname>:<device>:<autoconf>

  This parameter tells the kernel how to configure IP addresses of devices
  and also how to set up the IP routing table. It was originally called
  `nfsaddrs', but now the boot-time IP configuration works independently of
  NFS, so it was renamed to `ip' and the old name remained as an alias for
  compatibility reasons.

  If this parameter is missing from the kernel command line, all fields are
  assumed to be empty, and the defaults mentioned below apply. In general
  this means that the kernel tries to configure everything using
  autoconfiguration.

  The <autoconf> parameter can appear alone as the value to the `ip'
  parameter (without all the ':' characters before) in which case auto-
  configuration is used.

  <client-ip>   IP address of the client.

        Default:  Determined using autoconfiguration.

  <server-ip>   IP address of the NFS server. If RARP is used to determine
        the client address and this parameter is NOT empty only
        replies from the specified server are accepted.

        Only required for for NFS root. That is autoconfiguration
        will not be triggered if it is missing and NFS root is not
        in operation.

        Default: Determined using autoconfiguration.
                 The address of the autoconfiguration server is used.

  <gw-ip>   IP address of a gateway if the server is on a different subnet.

        Default: Determined using autoconfiguration.

  <netmask> Netmask for local network interface. If unspecified
        the netmask is derived from the client IP address assuming
        classful addressing.

        Default:  Determined using autoconfiguration.

  <hostname>    Name of the client. May be supplied by autoconfiguration,
        but its absence will not trigger autoconfiguration.

        Default: Client IP address is used in ASCII notation.

  <device>  Name of network device to use.

        Default: If the host only has one device, it is used.
             Otherwise the device is determined using
             autoconfiguration. This is done by sending
             autoconfiguration requests out of all devices,
             and using the device that received the first reply.

  <autoconf>    Method to use for autoconfiguration. In the case of options
                which specify multiple autoconfiguration protocols,
        requests are sent using all protocols, and the first one
        to reply is used.

        Only autoconfiguration protocols that have been compiled
        into the kernel will be used, regardless of the value of
        this option.

                  off or none: don't use autoconfiguration (default)
          on or any:   use any protocol available in the kernel
          dhcp:        use DHCP
          bootp:       use BOOTP
          rarp:        use RARP
          both:        use both BOOTP and RARP but not DHCP
                       (old option kept for backwards compatibility)

                Default: any

按照以上指示在命令行输入：

set bootargs noinitrd root=/dev/nfs nfsroot=202.204.53.70:/home/lvxiao/Nfs/fs_mini ip=202.204.53.71:202.204.53.70:202.204.53.1:255.255.255.0: :eth0:off init=/linuxrc console=ttySAC0

表示利用ubuntu系统上/home/lvxiao/Nfs文件夹下的fs_mini文件系统启动开发板，然后输入save命令保存，重新启动。