使用NFS作为根文件系统来启动

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

set bootargs  noinitrd root=/dev/nfs  nfsroot=192.168.1.102:/nfsboot/tmp/fs_mini_mdev   ip=192.168.1.108:192.168.1.102:192.168.1.1:255.255.255.0::eth0:off  init=/linuxrc console=ttySAC0

在内核目录下有个nfsboot.txt文件

/work/linux-2.6.22.6/Documentation/nfsboot.txt

内容如下：

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.