Creating iso files

On linux (& unix type boxes) it is easy to create an ISO file no extra software is needed, we use the dd command.  d(isk)d(ump) is one of the core gnu utilities and should be installed by default on all but the most lean implementations.

These are systems administration type tasks and must be done as root (su - to root, or sudo)

From a CDROM or DVD

1. Open a terminal session.
   
2. for a CD:  dd if=/dev/cdrom  of=thenameofmycd.iso
3. for a DVD: dd if=/dev/dvd  of=thenameofmydvd.iso  
   
   dd is disk dump, if is in file, of is out file

From a files on  disk drive

1. Open a terminal session.
2. mkisofs -o thenameofmy.iso      file(s) and/or directory(ies)
   
   n.b. mkisofs will create an hybrid file system (ISO9660  in this case)

These are the simplest forms of use for the two commands, use the man pages: 
*man dd
*man mkisofs