The main reason to clone disk images is to ease the installation of an operating system and a basic set of applications over a large number of machines. One standard machine is prepared and its pristine image is saved to be restored on other machines saving efforts and simplifying procedures.
Booting from hard disk would limit the possibilities of copying images. It wouldn't be possible, for instance, to safely copy to and from a partition mounted by the booted operating system. Also, the operating system may not be Linux, in which case free options to clone are not available.
The client machine boots from a Grub floppy disk. Then, using the Grub BOOTP support, it gets an IP address from a DHCP server. Next, the client machine downloads the kernel and initrd images from the TFTP server. Once the initrd image is mounted in memory, the initialization script is run, making use of the programs and files stored in this image. This script allows block devices contents to be saved in the TFTP server, and contents from the TFTP server to be written to the block devices.
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Created 1996-2021 by Maxim Chirkov
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