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Debian GNU/Linux Reference Guide
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9.3.7 Make an image file of a CD

Some CD-Rs and commercial CDs have junk sectors at the end that make copying by dd impossible (the Windows 98 CD is one of them). The cdrecord package comes with the readcd command. Use this to copy any CD contents to an image file. If it is a data disk, mount it and run df to see its actual size. Divide the number shown in blocks (1 block = 1024 bytes) by 2 to get the number of actual CD sectors (1 sector = 2048 bytes). Run readcd with options and use this disk image to burn the CD-R/RW.

     # readcd dev=target,lun,scsibusno # select function 11

Here, set all three parameters to 0 for most cases. Usually the number of sectors given by readcd is excessive! Use the above number from an actual mount for better results.

It should be noted that the use of dd has a few problems if used on CD-ROM. The first run of the dd command may cause an error message and may yield a shorter disk image with a lost tail-end. The second run of dd command may yield a larger disk image with garbage data attached at the end on some systems if the data size is not specified. Only the second run of the dd command with the correct data size specified, and without ejecting the CD after an error message, seems to avoid these problems. If for example the image size displayed by df is 46301184 blocks, use the following command twice to get the right image (this is my empirical information):

     # dd if=/dev/cdrom of=cd.img bs=2048 count=$((46301184/2))

Debian GNU/Linux Reference Guide
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