Weighing in at 689MB, the whole thing fits onto a
regular bootable CD. Now you might be thinking ???689MB.??¦there??™s no way that Linux
itself plus drivers for all kinds of hardware plus all the penetration testing tools I need
could possibly fit in 689MB.??? That??™s where the magic of the LiveCD system comes in.
BackTrack actually includes 2,700 MB??™s worth of stuff, but LiveCD does not run from the
CD itself. Instead, the Linux kernel and bootloader configuration live uncompressed on
the CD and allow the system to boot normally. After the kernel loads, a small ram disk is
created in the computer??™s RAM and the root-disk image (initrd.gz) is unpacked to the
ram disk and mounted as a root file system. And then finally larger directories (like /usr)
are mounted directly from the read-only CD. BackTrack uses a special file system (aufs)
allowing the read-only file system stored on the CD to behave like a writable one. It
saves all changes in memory. Aufs supports zlib compression, allowing everything to fit
on a regular CD-R.
BackTrack itself is quite complete and works well on a wide variety of hardware without
any changes. But what if a driver, a pen-testing tool, or an application you normally
use is not included? Or what if you want to store your home wireless access point
encryption key so you don??™t have to type it in every time? It works fine to download software
and make any configuration changes while the BackTrack CD is running, but those
changes don??™t persist to the next reboot because the real file system is read-only.
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