1da177e4c3
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
211 lines
7.8 KiB
Plaintext
211 lines
7.8 KiB
Plaintext
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.
|