掛載NFS： 一.單板啟動完成後進行掛載NFS 設定方法：     1.sudo vim /etc/exports開啟配置檔案，在檔案末尾加上目標資料夾例如：/home/work/nfs_root/nano_root *(rw,sync,no_root_squash)    (注意：這裡的路徑不能使用~來表示/home路徑)     2.重啟NFS服務sudo /etc/init.d/nfs-kernel-server restart     3.在單板上掛接NFS可執行sudo mount -t nfs -o nolock 192.168.31.140:/home/work/nfs_root/nano_root  /mnt

    4.此時執行ls /mnt即可顯示伺服器192.168.31.140:/home/work/nfs_root/nano_root中的內容。

二.單板啟動時自動掛載NFS目錄作為檔案系統     1.進入uboot中，設定root的位置     2.使用該命令設定root根檔案系統的位置 set bootargs noinitrd root=/dev/nfs nfsroot=192.168.31.140:/home/work/nfs_root/nano_root ip=192.168.31.30:192.168.31.140:192.168.1.1:255.255.255.0:eth0:off init=/linuxrc console=ttySAC0

linux 核心中的doumentation資料夾中有一個檔案nfsroot.txt來說明nfs掛載的方法：

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