How to Make an ISO Image Using DD
The basic syntax for dd is:
dd if=INPUT-FILE-NAME of=OUTPUT-FILE-NAME
To make an ISO from your CD/DVD, place the media in your drive but do not mount it. If it automounts, unmount it.
dd if=/dev/dvd of=dvd.iso # for dvd
dd if=/dev/cdrom of=cd.iso # for cdrom
dd if=/dev/scd0 of=cd.iso # if cdrom is scsi
To make an ISO from files on your hard drive, create a directory which holds the files you want. Then use the mkisofs command.
mkisofs -o /tmp/cd.iso /tmp/directory/
This results in a file called cd.iso in folder /tmp which contains all the files and directories in /tmp/directory/.