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PXE principles and concepts

2022-07-26 08:41:00 【a_ b_ e_ l_】

Pxe Principles and concepts

PXE Strictly speaking, it is not an installation method , It's a way of guiding . Conduct PXE The necessary condition for installation is that the computer to be installed contains a PXE Supported network cards （NIC）, That is, there must be PXE Client.PXE （Pre-boot Execution Environment） The protocol enables the computer to start over the network . The agreement is divided into client and server End ,PXE client On the network card ROM in , When the computer boots ,BIOS hold PXE client Call in memory to execute , from PXE client Download the files placed at the remote end to run locally through the network . function PXE The protocol needs to be set DHCP The server and TFTP The server .DHCP The server is used for PXE client（ take The host on which the system is to be installed ） Allocate one IP Address , Because it's for PXE client Distribute IP Address , So in configuration DHCP service It is necessary to increase the corresponding PXE Set up . Besides , stay PXE client Of ROM in , It already exists TFTP Client.PXE Client adopt TFTP The agreement reached TFTP Server Download the required files .

advantage ： scale ： Set up multiple servers at the same time ;

automation ： Install the system 、 Configure various services ;

Remote implementation ： You don't need a CD 、U Disk and other installation media .

Prerequisite

The client's network card supports PXE agreement （ Integrate BOOTROM chip ）, And the motherboard supports network boot . Ø There's one on the Internet DHCP Server to automatically assign addresses to clients 、 Specify the boot file location . Ø Server pass TFTP（Trivial File Transfer Protocol, Simple file transfer protocol ） Download the boot image file . among , The first condition is actually the hardware requirements , At present, most servers and most PC Can provide this support , Just in BIOS Setting allows you to set from Network or LAN Start it up .vlan： Virtual LAN

Ideas ：

1、dhcp Distribute IP

2、ftp （tftp vsftp ）tftp ： Download the boot image file vsftp： System installation files Customized boot mode pxelinux.cfg/default ——》 How to guide Define kernel boot 、 safe mode 、 test

3、 Image file

4、 Nobody is on duty kickstart service

Kickstart Concept

KickStart It's a kind of unattended installation .KickStart The working principle of is to record the manual work required in the typical installation process Pre filled parameters , And generate a file named ks.cfg The file of ; During the subsequent installation （ It's not just about generating KickStart Ann A machine for loading documents ） When a parameter is required to be filled , Setup will first find KickStart Generated files , When you find a match When appropriate parameters , Just use the parameters found , When no suitable parameter is found , It requires manual intervention by the installer . such , If KickStart The file covers all the parameters that need to be filled in during installation , The installer can just tell Where to get the installer ks.cfg file , Then go and do your own thing . After installation , The installation program will follow ks.cfg Reset set in Enable the option to restart the system , And end the installation .

Pxe working process

1.PXE The client sends DHCP request , towards DHCP Server application IP Address .

2.DHCP Server response PXE Client requests , Automatically from IP Allocate an address in the address pool IP Address to PXE The client , And tell PXE The client ：TFTP Server's IP Address and PXE Bootloader file pxelinux.0, Default in TFTP share directory /var/lib/tftpboot/ Next

3.PXE The client is going to TFTP The server initiates the acquisition pxelinux.0 Request for bootstrap file .

4.TFTP Server response PXE Client requests , Share it pxelinux.0 File transfer to PXE The client .5.PXE The client starts to the main interface of system installation through the network .

6.PXE Client to file sharing server （“ftp”、http、nfs etc. ） Initiate acquisition centos or windows Request for system installation files .

7.(vsftp) File sharing service response PXE Client requests , Transfer the shared system installation files to PXE The client .8.PXE The client enters the installation prompt wizard interface , Users need to manually complete the operation of system installation

Pxe build

1. Install and enable DHCP service

yum -y install dhcpcp -rfp /usr/share/doc/dhcp-4.2.5/dhcpd.conf.example /etc/dhcp/dhcpd.conf

Here you need to reset a network card

Here, set the newly added network card to host only mode , Use local vmnet1 network card , Then observe the address segment of this network card

Local here vmnet1 NIC ip Address set to 192.168.31.2, As dhcp Gateway to service .

Make the following settings in the configuration file ：

vim /etc/dhcp/dhcpd.conf

systemctl start dhcpd

systemctl enable dhcpd

2、 Install and enable TFTP service

TFTP：(Trivial File Transfer Protocol) Is a small and easy to implement file transfer protocol .TFTP Is based on UDP The datagram , We need to have our own corrective measures .TFTP Only file transfer is supported , No interaction supported , There is no huge command set . There is no directory list function , And the inability to authenticate users . But its code takes up less memory , You don't need a hard disk to cure TFTP Code , Very suitable for smaller computers and special-purpose equipment .

TFTP and FTP One major difference is that it has no interactive , Without authentication .

TFTP Generally used to transfer small files

yum -y install tftp-server

yum -y install xinetd

vim /etc/xinetd.d/tftp //tftp By xinet Escrow ,xinetd Not installed by default , The configuration file

xinetd namely extended internet daemon,xinetd Is a new generation of network daemons Services , It's also called super Internet The server . Often used to manage a variety of lightweight Internet service .xinetd Offer something similar to inetd+tcp_wrapper The function of , But stronger and safer

disable Set up no

be used for PXE Network installed Linux kernel 、 Driver files can be downloaded from CentOS 7 System CD / Image acquisition , Respectively vmlinuz and initrd.img, Located in the CD Directory images/pxeboot Next . Find these two files and copy them to tftp The root directory of the service

vmlinuz It's steerable 、 Compressed kernel .“vm” representative “Virtual Memory”.Linux Support virtual memory , It's not like the old operating system, like DOS Yes 640KB Memory limit .Linux Ability to use hard disk space as virtual memory , Hence the name “vm”.vmlinuz It's executable Linux kernel , It is located in /boot/vmlinuz, It is usually a soft link .

initrd yes “initial ramdisk” Abbreviation （ System initialization file ）. initrd It is usually used to temporarily boot hardware to the actual kernel vmlinuz The state of being able to take over and continue to guide .initrd.img It is mainly used to load ext4 And other file systems scsi Device drivers . such as , It uses scsi Hard disk , And the kernel vmlinuz There is no such thing in the scsi Hardware driver dynamic , Then load scsi Module before , The kernel cannot load the root file system , but scsi Modules are stored in the root file system /lib/modules Next . To solve this problem , You can boot a that can read the actual kernel initrd Kernel and use initrd correct scsi Guide questions .

# Get ready tftp Files that need to be shared

mount /dev/cdrom /mnt

cd /mnt/images/pxeboot/ # Kernel files The kernel initializes the image file /var/lib/tftpboot/ Site

cp initrd.img vmlinuz /var/lib/tftpboot/

systemctl start xinetd

systemctl enable xinetd

systemctl start tftp

systemctl enable tftp

The above is to convert the kernel file in the image + System initialization file Throw it tftp In the default shared directory , In order to follow up pxe-client To download

3、 Get ready PXE Bootstrap pxelinux.0

pxelinux.0 It's a binary , The main function is equivalent to the guidance of a system installation step , Guide the client how to install the system

yum provides */pxelinux.0 // Find out which package this file is installed by , Use when not a path and a package /

Yum install -y syslinux

cp /usr/share/syslinux/pxelinux.0 /var/lib/tftpboot/ # copy to tftp Under the root directory of , System boot file

4. Configure the Startup menu file

The Startup menu is used to guide the boot process of the client , Including how to call the kernel , How to load drivers . The default Startup menu file is default, Should be placed in tftp Root directory pxelinux.cfg subdirectory , The typical Startup menu configuration can be established automatically or manually by referring to the following operations . As for why /var/lib/tftpboot/pxelinux.cfg/default file , Because it was pxelinux.0 This document determines the good

mkdir /var/lib/tftpboot/pxelinux.cfg // Default pxelinux.cfg There is no need to manually create , Note that it is a directory, not a directory .cfg ending

Purely manual configuration default Menu file vim /var/lib/tftpboot/pxelinux.cfg/default