Abstract
This chapter describes how to install Mandriva Corporate Server 4 using the PXE (Pre-boot eXecution Environment) installation. You will learn how to configure the server and the client parts.
PXE is a protocol designed by Intel that allows computers to boot across a network. PXE is stored in the ROM of recent generation network cards. When the computer boots up, the BIOS loads the PXE ROM into memory and executes it. From the menu displayed, choose an entry for the computer to boot on an operating system loaded through the network.
PXE is implemented by network card vendors following Intel's specification. The following figure represents how it works using a DHCP server and a TFTP server.
Using PXE is quite easy, you need to follow these steps:
- Checking your hardware
-
First check your hardware so that it can use PXE functions. There is no universal way to do it. Your motherboard or network card documentation should specify it. You can also have a look in your BIOS settings, especially for onboard network devices. You will be able to enable or disable a “ROM option” on your network device (the specific method can be rather different depending on the BIOS). Also, in the boot order menu, make sure that the “network boot” is configured before the hard disk boot.
- Booting your system
If your PXE server is well configured, during the booting process, you should see all the 3 steps explained in the previous chapter. Then you should get a prompt:
boot:. Enter the label of the system you want to install and that's it.
![[Tip]](images/tip.png)
This server answers a special
DHCP request from the PXE client,
depending on the PXE client class. The location of the log files
varies according to your server's configuration. You can find them
in /var/log/messages. The default
configuration file is stored in the /etc
directory.
Here are classical options you need to configure:
- Allow booting
The booting flag is used to tell
dhcpdwhether or not to respond to queries from a particular client. This keyword only has meaning when it appears in a host declaration. By default, booting is allowed, but if it's disabled for a particular client, that client won't be able to get an address from the DHCP server.- Not authoritative
If the server is not valid for that segment it will send a
DHCPNACKmessage. This is important to set if you have other DHCP servers. If you want to install a PXE server in a network that already has a DHCP server, setting this option will insure that your DHCP answer will always be considered after the authoritative servers. This is usually used with a restricted PXE pool configuration (see below).- Pool
This section of
/etc/dhcpd.confdefines a pool which contains a range of IP addresses. In our example, the DHCP server allows members of the Class PXE, and denies members of other classes. The sample configuration (see below) restricts the address pool to the PXE clients. This insures that your DHCP will not respond to normal DHCP requests. This allows you to install a PXE server without conflicting with the master DHCP server. If you want to offer IP addresses to normal DHCP and PXE requests, just comment the “Allow member of PXE” line.
The PXE boot server also needs specific options for the DHCP server to work properly:
- Class
In our example, we create a PXE Class to determine specific options.
- Option vendor-class-identifier
If the
vendor-class-identifieroption of the DHCP request equals PXEClient, this class matches.- Vendor-option-space
- Filename
Option
filenamedefines the bootstrap client to retrieve. Our TFTP is chrooted so the path is relative to the chrooted directory only. Usually the file represents the PXElinux bootstrap. It's frequently called “linux.0” or “pxelinux.0”.- Next-server
It defines the IP of your TFTP server where the bootstrap and its configuration are stored.
- Set vendor_class_identifier
Set the vendor-class-identifier field to PXEClient in the DHCP answer. If this field is not set, the PXE client will ignore the answer!
ddns-update-style ad-hoc;
allow booting;
allow bootp;
not authoritative;
# Definition of PXE-specific options
option space PXE;
option PXE.mtftp-ip code 1 = ip-address;
option PXE.mtftp-cport code 2 = unsigned integer 16;
option PXE.mtftp-sport code 3 = unsigned integer 16;
option PXE.mtftp-tmout code 4 = unsigned integer 8;
option PXE.mtftp-delay code 5 = unsigned integer 8;
option PXE.discovery-control code 6 = unsigned integer 8;
option PXE.discovery-mcast-addr code 7 = ip-address;
class "PXE" {
match if substring(option vendor-class-identifier, 0, 9) = "PXEClient";
#filename "/PXEClient/pxegrub";
filename "/PXEClient/pxelinux.0";
option vendor-class-identifier "PXEClient";
vendor-option-space PXE;
option PXE.mtftp-ip 0.0.0.0;
next-server 192.168.200.1;
}
class "known" {
match hardware;
one-lease-per-client on;
ddns-updates on;
ddns-domainname = "mandriva.com";
ddns-hostname = pick-first-value(ddns-hostname, option host-name);
option fqdn.no-client-update on;
set vendor_class_identifier = option vendor-class-identifier;
}
shared-network "mynetwork" {
subnet 192.168.200.0 netmask 255.255.255.0 {
option subnet-mask 255.255.255.0;
option routers 192.168.200.1;
default-lease-time 28800;
max-lease-time 86400;
pool {
range 192.168.200.1 192.168.200.192;
allow members of "PXE";
}
}
}
The TFTP server contains the
bootstrap and the configuration files. It's launched by the
xinetd daemon. The default RPM
installation usually works without modifying anything, except that
it's not enabled by default. TFTP is managed by the
xinetd daemon, so you need to specify
that you want xinetd to open a
dedicated port. The xinetd
configuration for TFTP is in
/etc/xinetd.d/tftp. Open this file and change
disable=yes to
disabled=no. Finally restart
xinetd to take it into account:
service xinetd restart.
PXElinux is the PXE bootstrap. This bootstrap is downloaded by the client PXE ROM and executed locally. The aim of this PXE bootstrap is to give a minimalist user interface for choosing the system you want to boot. PXElinux is provided by the SYSLINUX project. The bootstrap is usually named “pxelinux.0” or “linux.0”. Main features are:
/var/lib/tftpboot
|-- X86PC
|-- linux
|-- help.txt
|-- images
| |-- 2006.0
| |-- all.rdz
| `-- vmlinuz
|-- linux.0
|-- memdisk
|-- messages
|-- pxelinux.cfg
|-- default
All the configuration files are
stored in the /X86PC/linux directory of the
TFTP server: /var/lib/tftpboot. You can
create a subdirectory that contains all the files needed by the
PXE client. The client is stored in
/var/lib/tftpboot/X86PC/linux (PXEPATH). So
your linux.0 should be in
PXEPATH and set in the dhcp configuration
file. Then create a pxelinux.cfg directory
in PXEPATH (CFGPATH).
The configuration directory
contains all the configuration files (one per PXE client IP
address) or a “default” configuration file. The
naming mechanism is to convert your IP address in hexadecimal
form: 192.168.200.1 gives you the name of
the “C0A8C801” CFGFILE. This file contains options
for the PXE client so that it will make the request with its
192.168.200.1 IP address. You can use the
gethostip script to do this
conversion.
In PXEPATH, create a directory
called images which will contain
subdirectories for each boot system
(e.g. linux for Linux boot images or a
kernel and its initrd). Each of these
contains a boot image or a kernel, its
initrd and a help file.
The PXE client downloads the
bootstrap (linux.0 in our case), executes it
locally and then tries to download its configuration CFGFILE
file. This file contains general options and boot images
definition. Here are its main options:
DEFAULT kernel optionsSets the default command line. If PXELINUX boots automatically, it will act just as if the entries after
DEFAULThad been typed in at thebootprompt, except that the optionautois automatically added, indicating an automatic boot.DISPLAY filenameDisplays the indicated file on the screen at boot time (before the
bootprompt is shown).TIMEOUT timeoutIndicates how long to wait at start-up. Timeout is canceled as soon as the user types anything on the keyboard, the assumption being that the user will complete the command line already begun. A timeout of zero completely disables the timeout, which is also the default behavior.
F[1-9] filenameWhen
F[1-9]is pressed, thenfilenameis displayed before going back to the prompt. It can be an easy way to provide help about boot images provided by the PXE server.
After having configured general
options, we now need to define images provided by the PXE
server. Each defined image starts with the
label option. It contains strings that can
be typed at the boot prompt. First, let's look at a specific image
that can allow booting a local system by forcing the PXE client
to exit.
label local
LOCALBOOT 0
The general syntax is
LOCALBOOT type. It executes a local disk
boot instead of booting a kernel. The argument
0 means to perform a normal boot on the next
boot device. The 4 argument performs a local
boot with the Universal Network Driver Interface
(UNDI) driver still resident in
memory. Finally, the 5 argument performs a
local boot with the entire PXE stack, including the
UNDI driver, still resident in memory. All
other values are undefined. If you don't know what the
UNDI or PXE stacks are, don't worry, you
don't want them: just specify 0.
label label
KERNEL image
APPEND options...
If label
is entered as the kernel boots, PXElinux should instead boot
image, and the specified
APPEND options should be used instead of the
ones specified in the global section of the file.
PXE can also allow you to
boot the kernel directly. The PXE client will download (using
a TFTP server) the kernel in the path given in the
KERNEL option, then it downloads the
initrd in the path given in the
APPEND initrd= option.
Then the PXE client executes
the kernel with the initrd and the option
given by the APPEND option.
This file should be stored in
CFGPATH and named like a
CFGFILE (e.g.
/var/lib/tftpboot/X86PC/linux/pxelinux.cfg/default or
/var/lib//tftpboot/X86PC/linux/pxelinux.cfg/C0A8C801)
PROMPT 1
DEFAULT local
DISPLAY messages
TIMEOUT 50
label local
LOCALBOOT 0
label linux
KERNEL memdisk
APPEND initrd=images/linux/network.img
label memtest
KERNEL images/memtest-1.60
label autoinstall
KERNEL images/autoinstall/vmlinuz
APPEND initrd=images/autoinstall/network.rdz ramdisk=32000 vga=788 kickstart=Mandrake/base/auto_inst.cfg.pl useless_thing_accepted automatic=method:nfs,network:dhcp,interface:eth0,dns:192.168.100.11,server:192.168.200.1,directory:/install root=/dev/ram3
F1 images/local/help.txt
F2 images/autoinstall/help.txt