What do you mean how to generate it ? It's like windows as far as I know . you simply download the Bootstrap.dat from a torrent and place it on Bitcoin Directory once you run your Bitcoin Core client , It start importing from Disk and split that file into other files (blocks) .
~ Madness
I've thought from time to time about producing a bootstrap.dat that extends to the current chain depth; the one that people are still getting off of the torrent is now over a year old.
But now we no longer need it. With version 0.10, we now have headers-first download, so it no longer matters. It's now about as fast to download using the bitcoin client as it is via bittorrent.