NFS-Root Mini-Howto

NFS-Root Mini-Howto
Andreas Kostyrka, [email protected]
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://sun-
site.unc.edu/pub/Linux/docs/HOWTO/mini/NFS-Root or on any sunsite mir-
ror NEAR YOU.
______________________________________________________________________

Table of Contents

1. Copyright

1.1 Contributors

2. General Overview

3. Setup on the server

3.1 Compiling the kernels
3.2 Creation of the root filesystem
3.2.1 Copying the filesystem
3.2.2 Changes to the root filesystem
3.2.3 Exporting the filesystem
3.2.4 RARP setup
3.2.5 BOOTP setup
3.2.6 Finding out hardware addresses

4. Booting the workstation

4.1 Using a boot rom
4.2 Using a raw kernel disc
4.3 Using a bootloader &
4.4 Using a bootloader without

5. Known problems

5.1 /sbin/init doesn't start.
5.2 /dev troubles.

6. Other topics

______________________________________________________________________

1. Copyright

(c) 1996 Andreas Kostyrka ([email protected] or
[email protected])

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.

All translations, derivative works, or aggregate works incorporating
any Linux HOWTO documents must be covered under this copyright notice.
That is, you may not produce a derivative work from a HOWTO and impose
additional restrictions on its distribution. Exceptions to these rules
may be granted under certain conditions; please contact the Linux
HOWTO coordinator at the address given below.

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:[email protected]>, the author of this mini-HOWTO, or Tim
Bynum, the Linux HOWTO coordinator, at <mailto:linux-
[email protected]> via email.

1.1. Contributors

o Avery Pennarun <[email protected]> (how to boot without LILO)

o Ofer Maor <[email protected]> (providing a better mini howto about
setting up discless workstations.)

o Christian Leutloff <[email protected]> (providing
infos about netboot.)

2. General Overview

Generally speaking there are the following problems for the
workstation:

o It must find out it's own IP-address, and if needed also the rest
of the Ethernet configuration.

o It must know the NFS-server and the mount path to it's root
filesystem.

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

o The IP-address may be discovered by RARP, or the full ethernet
configuration may be passed to the kernel via kernel parameters by
LILO or LOADLIN.

o The NFS-path to mount can be passed via kernel parameters. If this
is not done, the kernel assumes the RARP-server also as NFS-server,
and uses compiled in default for the path part. (current default
value in the kernel: /tftpboot/<IP-address of the machine>.)

o The client configuration may be discovered by BOOTP.

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:

o NFS-filesystem compiled in. (It doesn't need to have ext2-support
compiled in, a module suffices.)

o ``Root on NFS'' must be enabled.

o The Ethernet driver for the network card of the workstation must be
compiled in.

o Depending upon your needs you may have to include RARP or BOOTBP
support for NFS-Root. (By this I mean the questions that are asked
after the NFS question in make config.)

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

3.2.1. 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 <[email protected]>.

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.

3.2.2. Changes to the root filesystem

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

o One important thing is eth0 setup. The workstation comes up with a,
at least partially, setup eth0. Setting up the IP-address of the
workstation to the the IP-Address of the server is not considered a
clever thing to do. (As it happened to the author on one of his
early attempts.)

o Another point is the /etc/fstab of the workstation. It should be
setup for nfs filesystems.

o WARNING: Don't confuse the server root filesystem and the
workstation root filesystem. (I've already patched up a rc.inet1 on
the server, and wondered why the workstation still didn't work.)

3.2.3. 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 .

3.2.4. 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)

3.2.5. BOOTP setup

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

3.2.6. Finding out hardware addresses

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

o Boot the kernel disk you made, and watch for the line where the
network card is recognized. It usually contains 6 hex bytes, that
should be the address of the card.

o Boot the workstation with some OS with TCP/IP networking enabled.
Then ping the workstation from the server. Look in the ARP-cache by
executing: /sbin/arp -a

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
<[email protected]>):

o You can't use ``normal'' bootroms.

o There is a netboot packet by Gero Kuhlmann, that provides for
bootroms for Linux, and further information. netboot is available
from the local Linux mirror, or as a Debian package (netboot-0.4).

o Read the documentation coming with your boot rom carefully.

o You probably will have to enable the tftpd on the server, but this
depends upon your boot rom's way of loading the kernel.

o Any informations on bootrom vendors of these Linux variety,
mentioned above, as not everybody has access to prom burner :(
(especially in europe, as I'm located there.) welcome, I'll include
them then here.

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:

o When using LILO consider using the ``lock'' feature: Simply type in
once all the correct parameters and add ``lock''. Next time when
booting let LILO timeout.

o When generating a workstation specific boot disk, you can also use
the append= feature in lilo.conf.

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

o There is BOOTP client:
ftp://sunsite.unc.edu/system/Network/admin/bootpc.v045.tgz

With initrd (which is included in Linux 2.0), it could be made to
work for diskless stations quite nicely. initrd is actually always
an advanced option for more customized setups.

o For plain bootpd based boots this is actually probably not needed
as Linux 2.0 contains also the option to use BOOTP instead of RARP.
(To be more precise, you can compile both in the kernel, and the
faster response wins.)

o In the Documentation directory of kernel source there is a file
documenting NFS-Root systems.

o There is a patch floating around, that allows for swapping over
NFS. It was send to me (during a private high workload phase), but
I somehow managed to loose the mail. :(

You can get it probably from http://www.linuxhq.com/ in the
unofficial patches section.

o My PGP public key can be fetched by fingering [email protected].
The fingerprint is: F1 F7 43 D5 07 C4 6C 87 BF 6B 33 A2 2C EE 5A
F9.