文档时间：2018-08-25
交叉编译器：arm-linux-gcc-4.3.2
Ubuntu版本：16.04
kernel版本：linux-3.19
一，在 Ubuntu 上安装配置 NFS
1），安装 NFS
输入命令 sudo apt-get install nfs-kernel-server 安装 nfs-kernel-server：
输入命令 sudo apt-get install nfs-common 安装 nfs-common 这是挂载 nfs目录所需要的：
2），建立共享工作目录
输入命令：
/home/aaron/work mkdir nfs_root //建立工作目录 chmod 777 nfs_root //修改nfs_root权限
把制作好的根文件系统 fs_new 拷贝到 nfs_root 目录下
3），配置 NFS
打开 /etc/exports，添加如下内容：
/home/aaron/work/nfs_root *(rw,sync,no_root_squash,no_subtree_check)
* ： 允许所有的网段访问
rw ： 挂接此目录的客户端对该目录具有读写权限
sync ：资料同步
no_root_squash ：root 用户对文件目录具有完全访问权限
no_subtree_check ：不检查父目录的权限
配置完成后，重启 NFS 服务：sudo /etc/init.d/nfs-kernel-server restart
查看是否启动成功：showmount -e
如上图所示表示重启成功
4），验证
在 uboot 终端输入命令 nfs 32000000 192.168.2.110:/home/aaron/work/kernel/linux-3.19/arch/arm/boot/uImage 下载 uImage
下载成功
也可以通过在服务端挂载根文件系统来验证：
sudo mount -t nfs 192.168.2.110:/home/aaron/work/nfsroot/fs_new /mnt/
在服务端/mnt/目录下可以查看挂载到的文件系统
2，目标板通过 NFS 挂接根文件系统
(前提是内核已经支持网卡驱动，并且和服务端之间能够 ping 通，如果未移植 DM9000 驱动，可以参考：https://www.cnblogs.com/zhyy-mango/p/9527951.html)
1），目标板文件系统启动之后去挂载
命令如下：mount -t nfs -o nolock 192.168.2.110:/home/aaron/work/nfsroot/fs_new /mnt
2），修改 bootargs 直接从 nfs 启动
这种做法就是在u-boot启动之后，设置nfs挂载参数。首先必须掌握nfs命令：
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 nfs命令格式
然后根据nfs命令格式，具体格式解析要看nfs命令介绍：
nfsroot=[<server-ip>:]<root-dir>[,<nfs-options>] ip=<client-ip>:<server-ip>:<gw-ip>:<netmask>:<hostname>:<device>:<autoconf>
在 uboot 终端，输入以下命令来设置 bootargs：
set bootargs noinitrd root=/dev/nfs nfsroot=192.168.2.110:/home/aaron/work/nfs_root/fs_new/ ip=192.168.2.90:192.168.2.110:192.168.2.1:255.255.255.0::eth0:off init=/linuxrc console=ttySAC0,115200
然后 boot 启动，当文件系统启动后，就会与服务端共享 fs_new 目录下的东西