patch-1.3.82 linux/Documentation/nfsroot.txt

• Lines: 205
• Date: Mon Apr 1 10:46:29 1996
• Orig file: v1.3.81/linux/Documentation/nfsroot.txt
• Orig date: Thu Jan 1 02:00:00 1970

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+Mounting the root filesystem via NFS (nfsroot)
+==============================================
+
+Written 1996 by Gero Kuhlmann <gero@gkminix.han.de>
+
+
+
+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
+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 wether
+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.
+
+
+
+
+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:
+
+
+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 give 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
+		nfsaddrs 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.
+
+  <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.
+
+  <nfs-options>	Standard NFS options. All options are seperated by commas.
+		If the options field is not given, the following defaults
+		will be used:
+			port		= as given by server portmap daemon
+			rsize		= 1024
+			wsize		= 1024
+			timeo		= 7
+			retrans		= 3
+			acregmin	= 3
+			acregmax	= 60
+			acdirmin	= 30
+			acdirmax	= 60
+			flags		= hard, nointr, noposix, cto, ac
+
+
+nfsaddrs=<client-ip>:<server-ip>:<gw-ip>:<netmask>:<hostname>:<device>:<autoconf>
+
+  If this parameter is missing on the kernel command line, all fields are
+  assumed to be empty, and the below mentioned defaults 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).
+
+  <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.
+
+  <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 paremeter (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 in 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,
+		the netmask is derived from the client IP address, un-
+		less a value has been received by BOOTP.
+
+  <hostname>	Name of the client. If empty, the client IP address is
+		used in ASCII-notation, or the value received by BOOTP.
+
+  <device>	Name of network device to use. If this is empty, all
+		devices are used for RARP requests, and the first one
+		found for BOOTP. For NFS the device is used on which
+		either RARP or BOOTP replies have been received. If
+		you only have one device you can safely leave this blank.
+
+  <autoconf>	Method to use for autoconfiguration. If this is either
+		'rarp' or 'bootp' the specified protocol is being used.
+		If the value is 'both' or empty, both protocols are used
+		so far as they have been enabled during kernel configura-
+		tion. 'none' means no autoconfiguration. In this case you
+		have to specify all necessary values in the fields before.
+
+  The <autoconf> parameter can appear alone as the value to the nfsaddrs
+  parameter (without all the ':' characters before) in which case auto-
+  configuration is used. However, the 'none' value is not available in
+  that case.
+
+
+
+
+3.) Kernel loader
+    -------------
+
+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
+
+	Then copy the kernel zImage file onto a floppy using dd:
+
+		dd if=/usr/src/linux/arch/i386/boot/zImage of=/dev/fd0
+
+	And finally use rdev to set the root device:
+
+		rdev /dev/fd0 /dev/boot255
+
+	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 it's
+	root. If it got a BOOTP answer the directory name in that answer
+	is used.
+
+
+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
+	setup a dummy device as described in 3.1 above. How to use
+	LILO and it's '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 bootrom
+	This is probably the most elegant way of booting a diskless
+	client. With a bootrom the kernel gets loaded using the TFTP
+	protocol. As far as I know no commercial bootroms already
+	support booting Linux over the network, but there are two
+	free implementations of a bootrom available on sunsite.unc.edu
+	and it's mirrors. They are called 'netboot-nfs' and 'etherboot'.
+	Both contain everything you need to boot a diskless Linux client.
+
+
+
+
+4.) Credits
+    -------
+
+  The nfsroot code in the kernel has been written by me, Gero Kuhlmann
+  <gero@gkminix.han.de>, with the BOOTP code and a couple of bug fixes
+  contributed by Martin Mares <mj@k332.feld.cvut.cz>. In order to write
+  the initial version of nfsroot I would like to thank Jens-Uwe Mager
+  <jum@anubis.han.de> for his help.
+