hi all,
i want to boot from an encrypted partition, and also that while booting it shud not prompt for a password but passphrase shd be read from a pre-specified file.
Now man page of losetup says that
#losetup -p num(where num is the number corresponding to the file descriptor of file in which passphrase hasbeen stored)

how to get the num parameter,i.e how to find value for that parameter of the file????

ANY INPUT IS APPRECIATED