J'ai suivi la documentation de GRUB:
Here is an example of procedures to make a bootable CD-ROM image. First, make a top directory for the bootable image, say, `iso':
 
   
 
$ mkdir iso
 
Make a directory for GRUB:
 
   
 
$ mkdir -p iso/boot/grub
 
Copy the file `stage2_eltorito':
 
   
 
$ cp /usr/share/grub/i386-pc/stage2_eltorito iso/boot/grub
 
If desired, make the config file `menu.lst' under `iso/boot/grub' (see section 5. Configuration), and copy any files and directories for the disc to the directory `iso/'.
 
Finally, make a ISO9660 image file like this:
 
   
 
$ mkisofs -R -b boot/grub/stage2_eltorito -no-emul-boot \
    -boot-load-size 4 -boot-info-table -o grub.iso iso
 
 
Avec la derniere commande j'obtiens 
   ISO-8859-15 character encoding detected by locale settings.
        Assuming ISO-8859-15 encoded filenames on source filesystem,
        use -input-charset to override.
mkisofs: No such file or directory. Invalid node - iso