NFS-Root Mini-Howto

Andreas Kostyrka, andreas@ag.or.at

V8, 8 August 1997


This Mini-HOWTO tries explains how to setup a ``disc-less'' Linux workstation, which mounts it's root filesystems via NFS. The newest version of this Mini-Howto can always be found in ftp://sunsite.unc.edu/pub/Linux/docs/HOWTO/mini/NFS-Root or on any sunsite mirror NEAR YOU.

1. Copyright

2. General Overview

3. Setup on the server

4. Booting the workstation

5. Known problems

6. Other topics


1. Copyright

(c) 1996 Andreas Kostyrka (e9207884@student.tuwien.ac.at or andreas@ag.or.at)

Unless otherwise stated, Linux HOWTO documents are copyrighted by their respective authors. Linux HOWTO documents may be reproduced and distributed in whole or in part, in any medium physical or electronic, as long as this copyright notice is retained on all copies. Commercial redistribution is allowed and encouraged; however, the author would like to be notified of any such distributions.

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In short, we wish to promote dissemination of this information through as many channels as possible. However, we do wish to retain copyright on the HOWTO documents, and would like to be notified of any plans to redistribute the HOWTOs.

If you have questions, please contact Andreas Kostyrka <mailto:andreas@ag.or.at>, the author of this mini-HOWTO, or Tim Bynum, the Linux HOWTO coordinator, at <mailto:linux-howto@sunsite.unc.edu> via email.

1.1 Contributors


2. General Overview

Generally speaking there are the following problems for the workstation:

The current implementation of NFSROOT in the Linux kernel (as of 1.3.7x) allows for the following ``solutions'':

Before starting to setup a discless enviroment, you should decide if you will be booting via LILO or LOADLIN. The advantage of doing so is flexibility, the disadvantage is speed. Booting a Linux kernel without LILO is faster. This may or may not be a consideration.


3. Setup on the server

3.1 Compiling the kernels

RARP support in the kernel of the server will probably be a good idea. You must have it if you will boot without kernel parameters. On the other hand it doesn't help you, if the client isn't on the same subnet than the server.

The kernel for the workstation needs the following as a minimum set compiled in:

If the workstation will be booted without kernel parameters, you need also to set the root device to 0:255. Do this by creating a dummy device file with mknod /dev/nfsroot b 0 255. After having created such a device file, you can set root device of the kernel image with rdev <kernel-image> /dev/nfsroot.

3.2 Creation of the root filesystem

Copying the filesystem

Warning: while these instruction might work for you, they are by no means sensefull in a production enviroment. For a better way to setup a root filesystem for the clients, see the NFS-Root-Client mini howto by Ofer Maor <ofer@hadar.co.il>.

After having decided where to place the root tree, create it with (e.g.) mkdir -p <directory> and tar cClf / - | tar xpCf <directory> -.

If you boot your kernel without LILO, then the rootdir has to be /tftpboot/<IP-address>. If you don't like it, you can change it in the top Makefile in the kernel sources, look for a line like: NFS_ROOT = -DNFS_ROOT="\"/tftpboot/%s\"" If you change this, you have to recompile the kernel.

Changes to the root filesystem

Now trim the unneeded files, and check the /etc/rc.d scripts. Some important points:

Exporting the filesystem

Export the root dir to the work station. See exports(5). You most likely will have to restart the nfsd/mountd after this change. Under RedHat this can easily be done by typing /etc/rc.d/init.d/nfs stop ; /etc/rc.d/init.d/nfs start .

RARP setup

Setup the RARP somewhere on the net. If you boot without a nfsroot parameter, the RARP server has to be the NFS server. Usually this will be the NFS server. To do this, you will need to run a kernel with RARP support.

To do this, execute (and install it somewhere in /etc/rc.d of the server!):

/sbin/rarp -s <ip-addr> <hardware-addr>

where

ip-addr

is the IP address of the workstation, and

hardware-addr

is the Ethernet address of the network card of the workstation.

example: /sbin/rarp -s 131.131.90.200 00:00:c0:47:10:12

You can also use a symbolic name instead of the IP-address, as long the server is able to find out the IP-address. (/etc/hosts or DNS lookups)

BOOTP setup

For BOOTP setup you need to edit /etc/bootptab. Please consult the bootpd(8) and bootptab(5) man pages.

Finding out hardware addresses

I don't know the hardware address! How can I find it out?


4. Booting the workstation

4.1 Using a boot rom

As I have not used such a beast myself yet, I can give you only the following tips (courtesy of Christian Leutloff <leutloff@sundancer.tng.oche.de>):

4.2 Using a raw kernel disc

If you have exported the root filesystem with the correct name for the default naming and your NFS server is also the RARP server (which implies that the boxes are on the same subnet.), than you can just boot the kernel by cating it to a disc. (You have to set the root device in the kernel to 0:255.) This assumes, that the root directory on the server is /tftpboot/IP-Address (this value can be changed when compiling the kernel.)

4.3 Using a bootloader & RARP

Give the kernel all needed parameters when booting, and add nfsroot=<server-ip-addr>:</path/to/mount> where server-ip-addr is the IP-address of your NFS-server, and /path/to/mount is the path to the root directory.

Tips:

4.4 Using a bootloader without RARP

In addition to nfsroot give a nfsaddrs=<wst-IP>:<srv-IP>:<gw-IP>:<netm-IP>:<hostname> commandline argument for the kernel. The kernel will setup eth0 with the given parameters:

wst-IP

machine's IP-Address

srv-IP

NFS-server IP-Address

gw-IP

gateway

netm-IP

netmask

hostname

machine name


5. Known problems

5.1 /sbin/init doesn't start.

A popular problem with /sbin/init is, that some (at least) current distributions come with /sbin/init dynamically linked. So you have to provide a correct /lib setup to the client. One easy thing one could try is replacing /sbin/init (for the client) with a statically linked ``Hello World'' program. This way you know if it is something more basic, or ``just'' a problem with dynamic linking.

5.2 /dev troubles.

If you get some garbled messages about ttys when booting, then you should run a MAKEDEV from the client in the /dev directory. There are rumors that this doesn't work with certain server oses which use 64-bit dev numbers, should you run into this, please mail me with which os you have the troubles. A potential solution would be to create a small /dev ram disc early in the boot process, and reinstall the device nodes each time.


6. Other topics