First, list all the tools that may be used. There are too many things on the Internet and I don't know which one to use.
Squashfs-tools: http://tldp.org/HOWTO/SquashFS-HOWTO/index.html
Genisoimage: http://linux.die.net/man/1/genisoimage
Clonezilla: http://drbl.nchc.org.tw/clonezilla/
Debootstrap: http://wiki.debian.org/Debootstrap
Ucloner: Http://code.google.com/p/ucloner/
Ubuntu: Livecdcustomizationfromscratch
Tinyx: http://www.stevengibson.org/smalllinux/
Http://www.superant.com/smalllinux/tinyX01.html
Tinycorelinux: http://distro.ibiblio.org/pub/linux/distributions/tinycorelinux/4.x/x86/release/src/
Remastersys: http://www.remastersys.com /#
Unetbootin: http://unetbootin.sourceforge.net/inaccessible in China, but there are a lot of downloads on the network, mainly used to make liveusb
Yumi: http://www.pendrivelinux.com/more powerful than unetbootin, also easy to use, but can only be used in windows.
Fltk: http://www.fltk.org/
First, let's talk about how to back up the installed system or make it into an ISO installation file. The tool used here is remastersys, Which is powerful and easy to use. You can see it at a glance. After generating an ISO file with it, use Yumi-multiboot USB creator (Windows) to install it to USB, that is, to create a USB boot system.
When I test the custom-dist.iso in Ubuntu host, virtualbox VMS, I can start, but cannot enter the desktop. It is possible to start directly from USB. The system I installed is restored perfectly, and can be used without any configuration.