fedora core 6 1.2949 + vserver 2.2.0

[linux-2.6.git] / Documentation / nfsroot.txt

diff --git a/Documentation/nfsroot.txt b/Documentation/nfsroot.txt
index a87d4af..719f9a9 100644 (file)
--- a/Documentation/nfsroot.txt
+++ b/Documentation/nfsroot.txt
@@ -3,15 +3,17 @@ 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>
 
 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 Documentation/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.
 
 
 diskless system, and 'server' means the NFS server.
 
 


@@ -20,11 +22,13 @@ diskless system, and 'server' means the NFS server.
 1.) Enabling nfsroot capabilities
     -----------------------------
 
 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.

 
 
 
 
 
 


@@ -32,11 +36,10 @@ system you want to use. Selecting both BOOTP and RARP is safe.
 2.) Kernel command line
     -------------------
 
 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
 
 
 root=/dev/nfs


@@ -48,23 +51,21 @@ root=/dev/nfs
 
 nfsroot=[<server-ip>:]<root-dir>[,<nfs-options>]
 
 
 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.
 
   <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
                        port            = as given by server portmap daemon
                        rsize           = 1024
                        wsize           = 1024


@@ -80,119 +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
 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
 
   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
 
   <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
                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)
+
+                Default: any
+
+
+
+
+3.) Boot Loader
+    ----------

 
 

+To get the kernel into memory different approaches can be used.
+They depend on various facilities being available:

 
 
 
 

+3.1)  Booting from a floppy using syslinux

 
 

-3.) Kernel loader
-    -------------
+       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.

 
 

-To get the kernel into memory different approaches can be used. They
-depend on what facilities are available:
+       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

 
 

-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:
+       For more information on syslinux, including how to create bootdisks
+       for prebuilt kernels, see http://syslinux.zytor.com/

 
 

-               mknod /dev/boot255 c 0 255
+       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.

 
 

-       Then copy the kernel zImage file onto a floppy using dd:
+3.2) Booting from a cdrom using isolinux

 
 

-               dd if=/usr/src/linux/arch/i386/boot/zImage of=/dev/fd0
+       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.

 
 

-       And finally use rdev to set the root device:
+       e.g.
+         make isoimage FDARGS="root=/dev/nfs"

 
 

-               rdev /dev/fd0 /dev/boot255
+       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.

 
 

-       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.
+         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
 
 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.
-
-3.3) 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.
-
-3.4) 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.
+       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 using GRUB, kernel parameter are simply appended after the kernel
+       specification: kernel <kernel> <parameters>
+
+3.4) Using loadlin
+       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 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
+       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.
+       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/