12.7 Creating and Using Optical Media (CDs & DVDs)

Contributed by Mike Meyer.

12.7.1 Introduction

CDs have a number of features that differentiate them from conventional disks. Initially, they were not writable by the user. They are designed so that they can be read continuously without delays to move the head between tracks. They are also much easier to transport between systems than similarly sized media were at the time.

CDs do have tracks, but this refers to a section of data to be read continuously and not a physical property of the disk. To produce a CD on FreeBSD, you prepare the data files that are going to make up the tracks on the CD, then write the tracks to the CD.

The ISO 9660 filesystem was designed to deal with these differences. It unfortunately codifies filesystem limits that were common then. Fortunately, it provides an extension mechanism that allows properly written CDs to exceed those limits while still working with systems that do not support those extensions.

The sysutils/mkisofs program is used to produce a data file containing an ISO 9660 file system. It has options that support various extensions, and is described below. You can install it with the sysutils/mkisofs ports.

Which tool to use to burn the CD depends on whether your CD burner is ATAPI or something else. ATAPI CD burners use the burncd program that is part of the base system. SCSI and USB CD burners should use cdrecord from the sysutils/cdrtools port.

burncd has a limited number of supported drives. To find out if a drive is supported, see CD-R/RW supported drives.

12.7.2 mkisofs

sysutils/mkisofs produces an ISO 9660 filesystem that is an image of a directory tree in the Unix filesystem name space. The simplest usage is:

    # mkisofs -o imagefile.iso /path/to/tree

This command will create an imagefile containing an ISO 9660 filesystem that is a copy of the tree at /path/to/tree. In the process, it will map the file names to names that fit the limitations of the standard ISO 9660 filesystem, and will exclude files that have names uncharacteristic of ISO filesystems.

A number of options are available to overcome those restrictions. In particular, -R enables the Rock Ridge extensions common to Unix systems, -J enables Joliet extensions used by Microsoft systems, and -hfs can be used to create HFS filesystems used by MacOS.

For CDs that are going to be used only on FreeBSD systems, -U can be used to disable all filename restrictions. When used with -R, it produces a filesystem image that is identical to the FreeBSD tree you started from, though it may violate the ISO 9660 standard in a number of ways.

The last option of general use is -b. This is used to specify the location of the boot image for use in producing an ``El Torito'' bootable CD. This option takes an argument which is the path to a boot image from the top of the tree being written to the CD. So, given that /tmp/myboot holds a bootable FreeBSD system with the boot image in /tmp/myboot/boot/cdboot, you could produce the image of an ISO 9660 filesystem in /tmp/bootable.iso like so:

    # mkisofs -U -R -b boot/cdboot -o /tmp/bootable.iso /tmp/myboot

Having done that, if you have vn configured in your kernel, you can mount the filesystem with:

    # vnconfig -e vn0c /tmp/bootable.iso
    # mount -t cd9660 /dev/vn0c /mnt

At which point you can verify that /mnt and /tmp/myboot are identical.

There are many other options you can use with sysutils/mkisofs to fine-tune its behavior. In particular: modifications to an ISO 9660 layout and the creation of Joilet and HFS discs. See the mkisofs(8) manual page for details.

12.7.3 burncd

If you have an ATAPI CD burner, you can use the burncd command to burn an ISO image onto a CD. burncd is part of the base system, installed as /usr/sbin/burncd. Usage is very simple, as it has few options:

    # burncd -f cddevice data imagefile.iso fixate

Will burn a copy of imagefile.iso on cddevice. The default device is /dev/acd0c. See burncd(8) for options to set the write speed, eject the CD after burning, and write audio data.

12.7.4 cdrecord

If you do not have an ATAPI CD burner, you will have to use cdrecord to burn your CDs. cdrecord is not part of the base system; you must install it from either the port at sysutils/cdrtools or the appropriate package. Changes to the base system can cause binary versions of this program to fail, possibly resulting in a ``coaster''. You should therefore either upgrade the port when you upgrade your system, or if you are tracking -STABLE, upgrade the port when a new version becomes available.

While cdrecord has many options, basic usage is even simpler than burncd. Burning an ISO 9660 image is done with:

    # cdrecord dev=device imagefile.iso

The tricky part of using cdrecord is finding the dev to use. To find the proper setting, use the -scanbus flag of cdrecord, which might produce results like this:

    # cdrecord -scanbus
    Cdrecord 1.9 (i386-unknown-freebsd4.2) Copyright (C) 1995-2000 Jörg Schilling
    Using libscg version 'schily-0.1'
            0,0,0     0) 'SEAGATE ' 'ST39236LW       ' '0004' Disk
            0,1,0     1) 'SEAGATE ' 'ST39173W        ' '5958' Disk
            0,2,0     2) *
            0,3,0     3) 'iomega  ' 'jaz 1GB         ' 'J.86' Removable Disk
            0,4,0     4) 'NEC     ' 'CD-ROM DRIVE:466' '1.26' Removable CD-ROM
            0,5,0     5) *
            0,6,0     6) *
            0,7,0     7) *
            1,0,0   100) *
            1,1,0   101) *
            1,2,0   102) *
            1,3,0   103) *
            1,4,0   104) *
            1,5,0   105) 'YAMAHA  ' 'CRW4260         ' '1.0q' Removable CD-ROM
            1,6,0   106) 'ARTEC   ' 'AM12S           ' '1.06' Scanner
            1,7,0   107) *

This lists the appropriate dev value for the devices on the list. Locate your CD burner, and use the three numbers separated by commas as the value for dev. In this case, the CRW device is 1,5,0, so the appropriate input would be dev=1,5,0. There are easier ways to specify this value; see cdrecord(1) for details. That is also the place to look for information on writing audio tracks, controlling the speed, and other things.

12.7.5 Duplicating Audio CDs

You can duplicate an audio CD by extracting the audio data from the CD to a series of .wav files, and then writing these files to a blank CD. The process is slightly different for ATAPI and SCSI drives.

SCSI drives

  1. Use cdda2wav to extract the audio.

        % cdda2wav -v255 -D2,0 -B -Owav
  2. Use cdrecord to write the .wav files.

        % cdrecord -v dev=2,0 -dao -useinfo  *.wav

    Make sure that 2.0 is set appropriately, as described in Section 12.7.4.

ATAPI drives

  1. The ATAPI CD driver makes each track available as /dev/acddtn, where d is the drive number, and n is the track number. So the first track on the first disk is /dev/acd0t1.

    Make sure the appropriate files exist in /dev.

        # cd /dev
        sh MAKEDEV acd0t99
  2. Extract each track using dd(1).

        # dd if=/dev/acd0t1 of=track1.wav bs=2352
        # dd if=/dev/acd0t2 of=track2.wav bs=2352
  3. Burn the extracted files to disk using burncd. You must specify that these are audio files, and that burncd should fixate the disk when finished.

        # burncd -f /dev/acd0c audio track1.wav track2.wav ... fixate

12.7.6 Duplicating Data CDs

You can copy a data CD to a image file that is functionally equivalent to the image file created with sysutils/mkisofs, and you can use it to duplicate any data CD. The example given here assumes that your CDROM device is acd0. Substitute your correct CDROM device. A c must be appended to the end of the device name to indicate the entire partition or, in the case of CDROMs, the entire disc.

    # dd if=/dev/acd0c of=file.iso bs=2048

Now that you have an image, you can burn it to CD as described above.

12.7.7 Using Data CDs

Now that you have created a standard data CDROM, you probably want to mount it and read the data on it. By default, mount(8) assumes that a filesystem is of type ufs. If you try something like:

    # mount /dev/cd0c /mnt

you will get a complaint about ``Incorrect super block'', and no mount. The CDROM is not a UFS filesystem, so attempts to mount it as such will fail. You just need to tell mount(8) that the filesystem is of type ISO9660, and everything will work. You do this by specifying the -t cd9660 option mount(8). For example, if you want to mount the CDROM device, /dev/cd0c, under /mnt, you would execute:

    # mount -t cd9660 /dev/cd0c /mnt

Note that your device name (/dev/cd0c in this example) could be different, depending on the interface your CDROM uses. Also, the -t cd9660 option just executes mount_cd9660(8). The above example could be shortened to:

    # mount_cd9660 /dev/cd0c /mnt

You can generally use data CDROMs from any vendor in this way. Disks with certain ISO 9660 extensions might behave oddly, however. For example, Joliet disks store all filenames in two-byte Unicode characters. The FreeBSD kernel does not speak Unicode (yet!), so non-English characters show up as question marks. (If you are running FreeBSD 4.3 or later, the CD9660 driver includes hooks to load an appropriate Unicode conversion table on the fly. Modules for some of the common encodings are available via the sysutils/cd9660_unicode port.)

Occasionally, you might get ``Device not configured'' when trying to mount a CDROM. This usually means that the CDROM drive thinks that there is no disk in the tray, or that the drive is not visible on the bus. It can take a couple of seconds for a CDROM drive to realize that it has been fed, so be patient.

Sometimes, a SCSI CDROM may be missed because it didn't have enough time to answer the bus reset. If you have a SCSI CDROM please add the following option to your kernel configuration and rebuild your kernel.

    options SCSI_DELAY=15000

This tells your SCSI bus to pause 15 seconds during boot, to give your CDROM drive every possible chance to answer the bus reset.

12.7.8 Burning Raw Data CDs

You can choose to burn a file directly to CD, without creating an ISO 9660 filesystem. Some people do this for backup purposes. This runs more quickly than burning a standard CD:

    # burncd -f /dev/acd1c -s 12 data archive.tar.gz fixate

In order to retrieve the data burned to such a CD, you must read data from the raw device node:

    # tar xzvf /dev/acd1c

You cannot mount this disk as you would a normal CDROM. Such a CDROM cannot be read under any operating system except FreeBSD. If you want to be able to mount the CD, or share data with another operating system, you must use sysutils/mkisofs as described above.

This, and other documents, can be downloaded from ftp://ftp.FreeBSD.org/pub/FreeBSD/doc/.

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