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发信人: reden (鱼～看流星和她的故事), 信区: Linux
标  题: Linux Remote-Boot mini-HOWTO(4/7)
发信站: BBS 水木清华站 (Sun Oct 18 20:29:36 1998) WWW-POST

3. Introduction

The configuration described here was developped since Summer 1996 at the CUI,
University of Geneva. The Computer Science
Department uses several servers and a number of PCs, which fall into two
classes:

     computers devoted to students
     computers devoted to research and teaching assistants

We developped the current configuration with the following aims:

     Every computer should be able to run under Linux, DOS, Windows 3.1,
Windows 95 or Windows NT. One should be able
     to choose the desired operating system for each session.
     All softwares, including operating systems, should be take from the
server, in order to facilitate the installations and
     upgrades.
     Clients computers should be able to run without any write-access on the
server (for security reasons), except for their
     home directory.
     Client-side configuration should be reduced to its very minimum. Clients
should automatically get their IP configuration
     parameters from the server, and this information should be located in a
single file, used for all operating systems.
     Since almost every computer now has a hard-disk, clients should be able
to take profit of it for reducing network load and
     as temporary storage space for the user.
     Users must have a login to be able to use any of the computers.
     The login should be the same for all operating system and should let the
user access its unique home directory, common to
     all operating systems.
     Student (and secretary :-) computers should be fully cleaned up at each
start. That is, the PC should always look like if it
     were just installed.
     Every computer has to be protected from virus attacks.

These constraints lead us to base our configuration on bootprom tools. We
first developped new tools for the excellent TCP/IP
Bootprom from InCom GmbH. Now that a standard for preboot execution
environments as finally emerged, we ported the tools so
that it now also works for any PXE-compliant bootprom. PXE boot roms, also
called LanDesk Service Agent, are now distributed
with almost all on-board network adapter. For more info on PXE and Intel
Wired for Management standard in general, read from
http://www.intel.com/managedpc.

3.1 Boot ROM and Hard-disk

Bootproms exist for quite a long time, but until recently, they were solely
used with diskless computers. Since 1996, this How-to
has been claiming that bootproms are even more interesting for computers
which have a local harddisk, since they allow to take
profit of both sides:

     A boot rom make the configurations more robust, since it ensure that the
computer will always boot the same way, no
     matter any virus or partition table crash. It can be used, as we did, to
cleanup the harddisk even before the operating
     system is loaded.
     A local harddisk make the configuration more efficient, since it can
reduce the network trafic through caching, and allows
     for efficient swap.

Today, we have the pleasure to see that all computer manufacturers have come
to the same point and provide boot roms as part
of new computer standards.

Note that you can still use the tools described below in an old fashioned
way, that is as a simple kernel/ramdisk loader, even for
diskless computers. However, we do not encourage this use.

3.2 The Network

The University of Geneva owns a class B domain, subdivided into several
subnets. The CUI uses four subnets, among them one is
dedicated to students.

Originally, our PCs were concerned about two network protocols: IPX and IP.
On the IPX side, we used a single Novell Netware
3 server for sharing software and users files for DOS and Windows. On the IP
side, we used a SUN server for sharing software
and users partitions for Linux, with NFS.

In our latest configuration, we do not any more use IPX. There is a single
Unix server (which could be Linux as well as a SUN),
sharing software and user files using NFS for Linux clients and using SMB
(NetBIOS) over TCP/IP for Dos and Windows
clients. In this way, we have a single home directory used by all operating
systems.

3.3 How it Works

   1.When a client PC is turned on, it first performs the traditional system
checks before the TCP/IP Bootprom or PXE Boot
     ROM takes the control.
   2.The bootprom issues a BOOTP/DHCP request in order to get its IP
configuration parameters.
   3.If the server knows the PC issuing the request, it will send back a
BOOTP/DHCP reply with informations such as the
     client's IP address, the default gateway, and which bootdisk image to
use.
   4.In case of a PXE boot ROM, there might be some more exchanges between
the client and the server to determine
     installation parameters.
   5.The bootprom then downloads the boot image from the server using the
TFTP protocol. The boot image happens to be a
     small program called bpbatch, our boot-time batch file interpreter.
   6.The batch interpreter is started. At this time, it is almost alone in
the computer memory. There is no operating system
     loaded, except the preboot execution environment (offered by the Boot
ROM).
   7.The batch interpreter look in the BOOTP/DHCP reply for command-line
options, and in particular for the name of the
     batch to execute.
   8.According to the instructions in the batch file, it will for instance:
       1.Load a national keyboard mapping
       2.Authenticate the user according to a remote server (Unix, Radius or
Windows NT)
       3.Let the user choose between the available operating systems
       4.According to the operating system choosen, repartition the hard-disk
and quick-format some partitions
       5.Check if an up-to-date compressed image of the selected OS is
present at the end of the disk. If not, it download it
         using TFTP
       6.Uncompress the selected OS to the main partition
       7.If the selected OS is Linux, load a kernel and start it
       8.If the selected OS is DOS or Windows, simply let the computer boot
on its fresh new hard-disk
     For DOS and Windows 3.1, we use the freely available Microsoft
LanManager for DOS (search the network for the
     mirror nearest to you; the distribution consists of three files named
disk1 to disk4) as SMB client. Microsoft
     LanManager supports dynamic configuration using DHCP. After logging in,
the user is faced to DOS, and can start
     Windows 3.1 by typing the traditional win command. Note that at this
point, DOS and Windows 3.1 appear to be installed
     locally. For Windows 95 and Windows NT, we also use Microsoft SMB client
(called Client for the Microsoft
     Network), that supports dynamic configuration using DHCP. We reduce
network load using Shared LAN Cache, a nice
     and powerful network-to-disk cache program.

Students computers can be turned off the hard way at any time without risks,
since the hard disk is reinitialized at each start.

For "safe" computers (ie. for assistants computers), once the computer has
been booted once using the above described system,
the boot script simply redirect the boot to the local hard-disk, without
cleaning it again. This allow users to leave data on their local
hard disk. But whenever the configuration gets corrupted, the user can simply
choose from the boot menu in order to have a fresh
installation.

3.4 Related non-commercial documentations

This configuration has been successfully reproduced at several places around
the world. A few people have written some hints
and tricks that complement this How-To. If you did so and that your page is
not already referenced in this documentation, please
send an e-mail to Marc.VuilleumierStuckelberg@cui.unige.ch. And if you
experience problems while
reproducing this configuration, have a look at these pages !

     http://www.br.fgov.be/RESEARCH/INFORMATICS/info/bootp.html, by Alain
Empain of the Belgium
     National Botanic Garden. Many useful sample scripts, and a nice PERL
program to automatically generate graphic menus
     and corresponding HTML documentation from a higher level description.
     http://www.katedral.se/system/elevsyst, by Johan Carlstedt of The
Cathedral School of Uppsala,
     Sweden. At this day, the configuration described at this place is still
based on the previous version of the
     remote-boot tools. However, almost everything remains applicable, given
a few changes.
     http://vitoria.upf.tche.br/~fred/, in portuguese, by Frederico
Goldschmidt of the Passo Fundo University,
     Brasil.

You can also send me your BpBatch script if you want me to include it in the
sample scripts collection.

--
    白马带著她一步步的回到中原。白马已经老了，只能慢慢的走，
但终是能回到中原的。江南有杨柳、桃花，有燕子、金鱼……
汉人中有的是英俊勇武的少年，倜傥潇洒的少年……但这个美
丽的姑娘就像古高昌国人那样固执:

    「那都是很好很好的，可是我偏不喜欢。」

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