The magazine of the Melbourne PC User Group Creating an ISO image with Knoppix Major Keary

A reliable method of making a copy of a CD is by way of an .ISO image, which is a single file that contains the necessary components of the source CD and unpacks and writes them — in their correct order — to a target CD. Commercial CD/DVD burning applications create their own respective proprietary formats, but most (if not all) recognise .ISO image files. Nero provides a lessthan-intuitive write-to-image facility that produces an .NRG file, but it will burn from .ISO image files.

Linux has a simple way of creating an ISO image and which is available on Knoppix. There are a few preliminaries that you need to know about if using Knoppix.

First, where to put the image file; by default Knoppix will write files to the ramdisk that is created at start-up, which means that you lose data at shut-down unless it can be moved to a physical location such as a hard disk or USB storage device. The default Knoppix environment treats a system's hard drives and USB devices as read-only, so you have to find a way around that by changing permissions.

It is not difficult, and once the technique has been mastered the whole process of writing and saving an ISO image can be quick and reliable.

When Knoppix is fired up its desktop shows (figure 1) the system's various drives and partitions. The designations used may vary and this illustration of a Knoppix desktop reflects a system on which two CD/DVD drives are primary master and primary slave respectively and designated hda and hdb (but don't show up as such on the desktop). SCSI and USB storage devices are identified as sda, sdb, and so on. Hard drives are less easy to identify; on the system illustrated the Windows drive C: is designated as hde1 , and the following partitions on that disk jump to hde5, hde6, and so on. The drive that Windows would identify as D is hdf1 and any further partitions begin at hdf5. There is a logic behind that — it is not simply the inscrutable face of Linux — but there is not room to explore it here.

A simple way to work out which partition is which is to create an empty directory ('folder in Windows-speak) in each partition. Starting with C drive create a directory, AAA_C, or with as many As as necessary to ensure it is listed at the top of the directory tree. Similar empty directories (AAA_D, etc.) are used to identify the other disks/partitions. When looking at the contents of hdfl it is easy to confirm it is, for argument's sake, the Windows D drive. It may be crude, but is an effective navigational aid and is illustrated in figure 2.

To save an ISO file to, for example, D drive it is necessary to enable the write permission. Assuming the partition you want to use is hdf1, right click on the hdf1 icon and a drop-down menu appears as shown in figure 3. From the list select 'mount'. Get the menu back by right-clicking again and select 'change read/write mode'. A dialog box will appear (figure 4) asking for confirmation; check `ok'. You can now write directly to hdfl .
Place the target CD in a drive (don't try to use the one with the Knoppix disk). A dialog box will appear on the screen; just click on 'do nothing'. The CD drive is now mounted. Make a note of its designation (hd?). For the purpose of the exercise let us assume it is hdb.

The next step is to call up the console ("Konsole" in Knoppix) by clicking on the monitor icon at the bottom of the screen display (figure 2). This is the command-line interface.

The first step is to change directory: assuming you want to save the ISO file to hdf1, type:
         cd /media/hdf1
press the return key and the prompt line should show you are in hdf1.

Figure 5 shows the console screen with the change of directory, the command 'ls' (displays the directory), and the input described below.

Now enter (on one line):
        dd if=/dev/hdb of='targetcd.iso'
where "targetcd" is replaced by the name of the file to which the ISO image is to be saved. Press return.

There will be no feed-back by way of progress meters, but after a short time the command-line will report that the task has been completed and the new file will appear in the directory listing. The single quotes are not necessary in this instance, but provide a belt-and-braces safeguard in case the file name contains some special character(s).

That may seem complicated and convoluted, but once you have done it a couple of times the process is simple and fast. Just remember that, under Knoppix, to do anything but read files requires the partition or device to be mounted and the read/write mode to be enabled. You can drag-and-drop in Knoppix provided write permissions have been set, such as in the manner described.

While Knoppix, in common with other Linux desktop distros, can burn CDs from ISO images, the procedure described is particularly useful for creating portable image files that can be burned to CD on any other platform.

Reprinted from the September 2007 issue of PC Update, the magazine of Melbourne PC User Group, Australia

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