[PATCH] nfs: Update Documentation/nfsroot.txt to include dhcp, syslinux and isolinux

* Document the ip command a little differently to make the
  interaction between defaults and autoconfiguration a little clearer
  (I hope)

* Update autoconfiguration the current set of options, including DHCP

* Update the boot methods to add syslinux and isolinux, and remove
  dd of=/dev/fd0 which is no longer supported by linux

* Add a referance to initramfs along side initrd.
  Should the latter and its document be removed some time soon?

* Various cleanups to put the text consistently into the thrid person

* Reformated a bit to fit into 80 columns a bit more nicely

* Should the bootloaders documentation be removed or split
  into a separate documentation, it seems somewhat out of scope

Signed-off-by: Horms <horms@verge.net.au>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 160 insertions, 115 deletions

diff --git a/Documentation/nfsroot.txt b/Documentation/nfsroot.txt
index d56dc71d9430..3cc953cb288f 100644
--- a/Documentation/nfsroot.txt
+++ b/Documentation/nfsroot.txt
@@ -4,15 +4,16 @@ Mounting the root filesystem via NFS (nfsroot)
 Written 1996 by Gero Kuhlmann <gero@gkminix.han.de>
 Updated 1997 by Martin Mares <mj@atrey.karlin.mff.cuni.cz>
 Updated 2006 by Nico Schottelius <nico-kernel-nfsroot@schottelius.org>
+Updated 2006 by Horms <horms@verge.net.au>
 
 
 
-If you want to use a diskless system, as an X-terminal or printer
-server for example, you have to put your root filesystem onto a
-non-disk device. This can either be a ramdisk (see initrd.txt in
-this directory for further information) or a filesystem mounted
-via NFS. The following text describes on how to use NFS for the
-root filesystem. For the rest of this text 'client' means the
+In order to use a diskless system, such as an X-terminal or printer server
+for example, it is necessary for the root filesystem to be present on a
+non-disk device. This may be an initramfs (see Documentation/filesystems/
+ramfs-rootfs-initramfs.txt), a ramdisk (see Documenation/initrd.txt) or a
+filesystem mounted via NFS. The following text describes on how to use NFS
+for the root filesystem. For the rest of this text 'client' means the
 diskless system, and 'server' means the NFS server.
 
 
@@ -21,11 +22,13 @@ diskless system, and 'server' means the NFS server.
 1.) Enabling nfsroot capabilities
     -----------------------------
 
-In order to use nfsroot you have to select support for NFS during
-kernel configuration. Note that NFS cannot be loaded as a module
-in this case. The configuration script will then ask you whether
-you want to use nfsroot, and if yes what kind of auto configuration
-system you want to use. Selecting both BOOTP and RARP is safe.
+In order to use nfsroot, NFS client support needs to be selected as
+built-in during configuration. Once this has been selected, the nfsroot
+option will become available, which should also be selected.
+
+In the networking options, kernel level autoconfiguration can be selected,
+along with the types of autoconfiguration to support. Selecting all of
+DHCP, BOOTP and RARP is safe.
 
 
 
@@ -33,11 +36,10 @@ system you want to use. Selecting both BOOTP and RARP is safe.
 2.) Kernel command line
     -------------------
 
-When the kernel has been loaded by a boot loader (either by loadlin,
-LILO or a network boot program) it has to be told what root fs device
-to use, and where to find the server and the name of the directory
-on the server to mount as root. This can be established by a couple
-of kernel command line parameters:
+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
@@ -49,23 +51,21 @@ root=/dev/nfs
 
 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.
+  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. If this field
-                is not given, the default address as determined by the
-                `ip' variable (see below) is used. One use of this
-                parameter is for example to allow using different servers
-                for RARP and NFS. Usually you can leave this blank.
+  <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, the token will be
-                replaced by the ASCII-representation of the client's IP
-                address.
+  <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.
-                If the options field is not given, the following defaults
-                will be used:
+                The following defaults are used:
                         port            = as given by server portmap daemon
                         rsize           = 1024
                         wsize           = 1024
@@ -81,129 +81,174 @@ nfsroot=[<server-ip>:]<root-dir>[,<nfs-options>]
 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.
+  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 both
-  RARP and BOOTP (depending on what has been enabled during kernel confi-
-  guration, and if both what protocol answer got in first).
+  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.
 
-  <client-ip>   IP address of the client. If empty, the address will either
-                be determined by RARP or BOOTP. What protocol is used de-
-                pends on what has been enabled during kernel configuration
-                and on the <autoconf> parameter. If this parameter is not
-                empty, neither RARP nor BOOTP will be used.
+                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. To use
-                different RARP and NFS server, specify your RARP server
-                here (or leave it blank), and specify your NFS server in
-                the `nfsroot' parameter (see above). If this entry is blank
-                the address of the server is used which answered the RARP
-                or BOOTP request.
-
-  <gw-ip>       IP address of a gateway if the server is on a different
-                subnet. If this entry is empty no gateway is used and the
-                server is assumed to be on the local network, unless a
-                value has been received by BOOTP.
-
-  <netmask>     Netmask for local network interface. If this is empty,
+                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, unless overridden in BOOTP reply.
+                classful addressing.
 
-  <hostname>    Name of the client. If empty, the client IP address is
-                used in ASCII notation, or the value received by BOOTP.
+                Default:  Determined using autoconfiguration.
 
-  <device>      Name of network device to use. If this is empty, all
-                devices are used for RARP and BOOTP requests, and the
-                first one we receive a reply on is configured. If you have
-                only one device, you can safely leave this blank.
+  <hostname>    Name of the client. May be supplied by autoconfiguration,
+                but its absence will not trigger autoconfiguration.
 
-  <autoconf>    Method to use for autoconfiguration. If this is either
-                'rarp' or 'bootp', the specified protocol is used.
-                If the value is 'both' or empty, both protocols are used
-                so far as they have been enabled during kernel configura-
-                tion. 'off' means no autoconfiguration.
+                Default: Client IP address is used in ASCII notation.
 
-  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.
+  <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)
 
-3.) Kernel loader
-    -------------
+                Default: any
 
-To get the kernel into memory different approaches can be used. They
-depend on what facilities are available:
 
 
-3.1)  Writing the kernel onto a floppy using dd:
-        As always you can just write the kernel onto a floppy using dd,
-        but then it's not possible to use kernel command lines at all.
-        To substitute the 'root=' parameter, create a dummy device on any
-        linux system with major number 0 and minor number 255 using mknod:
 
-                mknod /dev/boot255 c 0 255
+3.) Boot Loader
+    ----------
 
-        Then copy the kernel zImage file onto a floppy using dd:
+To get the kernel into memory different approaches can be used.
+They depend on various facilities being available:
 
-                dd if=/usr/src/linux/arch/i386/boot/zImage of=/dev/fd0
 
-        And finally use rdev to set the root device:
+3.1)  Booting from a floppy using syslinux
 
-                rdev /dev/fd0 /dev/boot255
+        When building kernels, an easy way to create a boot floppy that uses
+        syslinux is to use the zdisk or bzdisk make targets which use
+        and bzimage images respectively. Both targets accept the
+        FDARGS parameter which can be used to set the kernel command line.
 
-        You can then remove the dummy device /dev/boot255 again. There
-        is no real device available for it.
-        The other two kernel command line parameters cannot be substi-
-        tuted with rdev. Therefore, using this method the kernel will
-        by default use RARP and/or BOOTP, and if it gets an answer via
-        RARP will mount the directory /tftpboot/<client-ip>/ as its
-        root. If it got a BOOTP answer the directory name in that answer
-        is used.
+        e.g.
+           make bzdisk FDARGS="root=/dev/nfs"
+
+        Note that the user running this command will need to have
+        access to the floppy drive device, /dev/fd0
+
+        For more information on syslinux, including how to create bootdisks
+        for prebuilt kernels, see http://syslinux.zytor.com/
+
+        N.B: Previously it was possible to write a kernel directly to
+             a floppy using dd, configure the boot device using rdev, and
+             boot using the resulting floppy. Linux no longer supports this
+             method of booting.
+
+3.2) Booting from a cdrom using isolinux
+
+        When building kernels, an easy way to create a bootable cdrom that
+        uses isolinux is to use the isoimage target which uses a bzimage
+        image. Like zdisk and bzdisk, this target accepts the FDARGS
+        parameter which can be used to set the kernel command line.
+
+        e.g.
+          make isoimage FDARGS="root=/dev/nfs"
+
+        The resulting iso image will be arch/<ARCH>/boot/image.iso
+        This can be written to a cdrom using a variety of tools including
+        cdrecord.
+
+        e.g.
+          cdrecord dev=ATAPI:1,0,0 arch/i386/boot/image.iso
+
+        For more information on isolinux, including how to create bootdisks
+        for prebuilt kernels, see http://syslinux.zytor.com/
 
 3.2) Using LILO
-        When using LILO you can specify all necessary command line
-        parameters with the 'append=' command in the LILO configuration
-        file. However, to use the 'root=' command you also need to
-        set up a dummy device as described in 3.1 above. For how to use
-        LILO and its 'append=' command please refer to the LILO
-        documentation.
+        When using LILO all the necessary command line parameters may be
+        specified using the 'append=' directive in the LILO configuration
+        file.
+
+        However, to use the 'root=' directive you also need to create
+        a dummy root device, which may be removed after LILO is run.
+
+        mknod /dev/boot255 c 0 255
+
+        For information on configuring LILO, please refer to its documentation.
 
 3.3) Using GRUB
-        When you use GRUB, you simply append the parameters after the kernel
-        specification: "kernel <kernel> <parameters>" (without the quotes).
+        When using GRUB, kernel parameter are simply appended after the kernel
+        specification: kernel <kernel> <parameters>
 
 3.4) Using loadlin
-        When you want to boot Linux from a DOS command prompt without
-        having a local hard disk to mount as root, you can use loadlin.
-        I was told that it works, but haven't used it myself yet. In
-        general you should be able to create a kernel command line simi-
-        lar to how LILO is doing it. Please refer to the loadlin docu-
-        mentation for further information.
+        loadlin may be used to boot Linux from a DOS command prompt without
+        requiring a local hard disk to mount as root. This has not been
+        thoroughly tested by the authors of this document, but in general
+        it should be possible configure the kernel command line similarly
+        to the configuration of LILO.
+
+        Please refer to the loadlin documentation for further information.
 
 3.5) Using a boot ROM
-        This is probably the most elegant way of booting a diskless
-        client. With a boot ROM the kernel gets loaded using the TFTP
-        protocol. As far as I know, no commercial boot ROMs yet
-        support booting Linux over the network, but there are two
-        free implementations of a boot ROM available on sunsite.unc.edu
-        and its mirrors. They are called 'netboot-nfs' and 'etherboot'.
-        Both contain everything you need to boot a diskless Linux client.
+        This is probably the most elegant way of booting a diskless client.
+        With a boot ROM the kernel is loaded using the TFTP protocol. The
+        authors of this document are not aware of any no commercial boot
+        ROMs that support booting Linux over the network. However, there
+        are two free implementations of a boot ROM, netboot-nfs and
+        etherboot, both of which are available on sunsite.unc.edu, and both
+        of which contain everything you need to boot a diskless Linux client.
 
 3.6) Using pxelinux
-        Using pxelinux you specify the kernel you built with
+        Pxelinux may be used to boot linux using the PXE boot loader
+        which is present on many modern network cards.
+
+        When using pxelinux, the kernel image is specified using
         "kernel <relative-path-below /tftpboot>". The nfsroot parameters
         are passed to the kernel by adding them to the "append" line.
-        You may perhaps also want to fine tune the console output,
-        see Documentation/serial-console.txt for serial console help.
+        It is common to use serial console in conjunction with pxeliunx,
+        see Documentation/serial-console.txt for more information.
+
+        For more information on isolinux, including how to create bootdisks
+        for prebuilt kernels, see http://syslinux.zytor.com/