2.) Kernel command line
    -------------------

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).  If the value is
  "ip=off" or "ip=none", no autoconfiguration will take place, otherwise
  autoconfiguration will take place.  The most common way to use this
  is "ip=dhcp".

  <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
                                (do static IP assignment instead)
                  on or any:   use any protocol available in the kernel
                               (default)
                  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