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diff --git a/Documentation/nfsroot.txt b/Documentation/nfsroot.txt new file mode 100644 index 0000000..a87d4af --- /dev/null +++ b/Documentation/nfsroot.txt @@ -0,0 +1,210 @@ +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> + + + +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 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. + + + + +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 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. + + <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 separated 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 + + +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 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' 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, + the netmask is derived from the client IP address assuming + classful addressing, unless overridden in BOOTP reply. + + <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 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. + + <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. + + 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. + + + + +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 its + 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 + 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. + + + + +4.) Credits + ------- + + The nfsroot code in the kernel and the RARP support have been written + by Gero Kuhlmann <gero@gkminix.han.de>. + + The rest of the IP layer autoconfiguration code has been written + by Martin Mares <mj@atrey.karlin.mff.cuni.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. |
