The Linux CD-ROM HOWTO

1.1. Acknowledgments

Much of this information came from the documentation and source files provided with the Linux kernel, the Internet alt.cdrom newsgroup FAQ, and input from Linux users.

Thanks to the DocBook tools, this HOWTO is available in several formats, all generated from a common source file.

1.2. New Versions Of This Document

New versions of this document will be periodically posted to the comp.os.linux.answers newsgroup. Hypertext versions of this and other Linux HOWTOs are available on many world-wide web sites, including http://www.linuxdoc.org. Most Linux CD-ROM distributions include the HOWTOs, often under the /usr/doc directory, and you can also buy printed copies from several vendors. Sometimes the HOWTOs available from CD-ROM vendors, ftp sites, and printed format are out of date. If the date on this HOWTO is more than six months in the past, then a newer copy is probably available on the Internet.

Please note that, due to the dynamic nature of the Internet, all web and ftp links listed in this document are subject to change.

Translations of this document are available in several languages:

Chinese: http://www.linux.org.tw/CLDP/CDROM-HOWTO.html

French: http://www.freenix.org/unix/linux/HOWTO/

German: http://www.tu-harburg.de/dlhp/HOWTO/DE-CDROM-HOWTO.html

Korean: http://kldp.org/HOWTO/html/CDROM/CDROM-HOWTO.html

Japanese: http://www.linux.or.jp/JF/JFdocs/CDROM-HOWTO.html

Polish: http://www.jtz.org.pl/Html/CDROM-HOWTO.pl.html

Spanish: ftp://ftp.insflug.org/es

Swedish: ftp://ftp.hig.se/pub/linux/swe-doc/

Most translations of this and other Linux HOWTOs can also be found at http://www.ibiblio.org/pub/Linux/docs/HOWTO/translations/. If you make a translation of this document into another language, let me know and I'll include a reference to it here.

1.3. Feedback

I rely on you, the reader, to make this HOWTO useful. If you have any suggestions, corrections, or comments, please send them to me, tranter@pobox.com, and I will try to incorporate them in the next revision.

I am also willing to answer general questions on CD-ROM under Linux, as best I can. Before doing so, please read all of the information in this HOWTO, and then send me detailed information about the problem. Please do not ask me about using CD-ROM drives under operating systems other than Linux.

If you publish this document on a CD-ROM or in hardcopy form, a complimentary copy would be appreciated; mail me for my postal address. Also consider making a donation to the Linux Documentation Project to help support free documentation for Linux. Contact the LDP at feedback@linuxdoc.org for more information.

1.4. Distribution Policy

Copyright (c) 1995-2001 by Jeff Tranter. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is available at http://www.gnu.org/copyleft/fdl.html

3.1. ATAPI CD-ROM Drives

ATAPI (ATA Packet Interface) is a protocol for controlling mass storage devices. It builds on the ATA (AT Attachment) interface, the official ANSI standard name for the IDE interface developed for hard disk drives. ATAPI is commonly used for hard disks, CD-ROM drives, tape drives, and other devices. Currently the most popular type of interface, it offers most of the functionality of SCSI, without the need for an expensive controller or cables.

The Linux kernel has a device driver that should work with any ATAPI compliant CD-ROM drive. Vendors shipping compatible drives include Aztech, Mitsumi, NEC, Sony, Creative Labs, and Vertos. If you have recently purchased a CD-ROM drive, especially if it is quad speed or faster, it is almost guaranteed to be IDE/ATAPI.

Linux also has an IDE SCSI emulation kernel driver that makes an IDE/ATAPI device appear in software to be a SCSI device, allowing the use of a SCSI device driver instead of the native ATAPI driver. This is useful if you have an ATAPI device for which no native driver has been written (for example, an ATAPI PD-CD or CDR drive); you can then use this emulation together with an appropriate SCSI device driver.

3.2. SCSI CD-ROM Drives

SCSI (Small Computer Systems Interface) is a popular format for CD-ROM drives. Its chief advantages are a reasonably fast transfer rate, multi-device capability, and support on a variety of computer platforms. Some disadvantages of SCSI are the need for a relatively expensive controller card and cables.

Any SCSI CD-ROM drive with a block size of 512 or 2048 bytes should work under Linux; this includes the vast majority of CD-ROM drives on the market.

You will also need a supported SCSI controller card; see the Linux SCSI HOWTO for more information on interface hardware.

Note that some older CD-ROM drives use a proprietary controller with a modified interface that is not fully SCSI compatible (e.g. it may not support adding other SCSI devices on the bus). These will most likely not work under Linux.

3.3. Proprietary CD-ROM Drives

Several CD-ROM drives using proprietary interfaces are available; the interface is often provided on a sound card. Simple interface cards equivalent to that provided on the sound card are also available. These drives generally tend to be lower in cost and smaller than SCSI drives. Their disadvantages are the lack of standardization and expandability.

Note that proprietary interfaces are sometimes erroneously referred to as IDE interfaces, because like IDE hard disks, they use a simple interface based on the PC/AT bus. To add to the confusion, some vendors, most notably Creative Labs, have shipped many different types of CD-ROM drives and have offered proprietary, SCSI, and ATAPI interfaces on their sound cards.

The table below lists the proprietary CD-ROM drives that are known to be supported under Linux. Drivers for additional devices may be available in the latest development kernels or as kernel patches. The latter can most often be found at ftp://www.ibiblio.org/pub/Linux/kernel/patches/cdrom/. Also check the documentation files included with the kernel distribution, usually installed in /usr/src/linux/Documentation/cdrom, for the latest information.

1. These drives may be sold under the names Creative Labs, Panasonic, Matsushita, or Kotobuki.

2. This drive is the same as a Panasonic CR-562.

3. May also be sold under the Procomm name.

4. This driver is for the CDA268-01A only. Other models, including the CDA268-03I and CDA269-031SE are not proprietary and should use the IDECD (ATAPI) kernel driver.

5. May also be sold as part of a Reveal Multimedia Kit.

6. The Philips CM205 is not supported by this driver, but there is a separate alpha release driver available from ftp://www.ibiblio.org in /pub/Linux/kernel/patches/cdrom/lmscd0.4.tar.gz

7. May also be sold under the Radio Shack name.

8. There are two drivers available. "mcd" is the original one, and "mcdx" is a newer driver with more features (XA and multi-session support).

9. This driver works with CD-ROM drives that are attached to the interface on an ISP16, MAD16 or Mozart sound card.

If a drive listed here is not supported by your kernel, you probably need to upgrade to a newer version.

If your drive is not one of the models listed here, particularly if it was bought recently and is quad speed or faster, it probably uses the IDE/ATAPI interface listed in a previous section. The single most common error among Linux CD-ROM users is to assume that any drive connected to a SoundBlaster card should use the SBPCD driver. Creative Labs and most other vendors are no longer selling proprietary interface drives, they are following the standard ATAPI/IDE interface.

3.4. Parallel Port Drives

There are external storage devices, including CD-ROM drives, that attach to the parallel port of personal computers. In many cases the devices internally use an IDE interface in conjunction with an adaptor which interfaces the internal IDE bus to the PC parallel port.

Linux has a parallel port IDE driver which supports most parallel port devices. At the time of writing it supported devices from the following vendors (as well as most no-name and clone drives compatible with these): ATEN, Avatar, DataStor, Fidelity International Technology, Freecom, Hewlett-Packard, Imation, KT Technology, KingByte Information Corp., Maxell, MicroSolutions, OnSpec, Shuttle Technology, SyQuest, and ValuStore.

Additional information can be found at http://www.torque.net/parport/.

3.5. PCMCIA Drives

Using a PCMCIA SCSI or IDE adaptor you can connect external CD-ROM drives to a laptop. Once the appropriate PCMCIA kernel driver is installed the drives will appear like any other IDE or SCSI drives.

See the Linux PCMCIA HOWTO for more information.

3.6. USB CD-ROM Drives

The Universal Serial Bus has support for mass storage devices. USB CD-R and CD-RW drives are popular because they can be quickly and easily moved between systems.

You need to configure the kernel for "USB Mass Storage support". This makes USB storage devices appear like SCSI, although they do not use the same device files. See the Linux USB HOWTO for more details.

4.1. Installing the Hardware

Follow the manufacturer's instructions for installing the hardware or have your dealer perform the installation. The details will vary depending on whether the drive is internal or external and on the type of interface used. There are no special installation requirements for Linux. You may need to set jumpers on the drive and/or interface card for correct operation; some of the kernel drivers include documentation files that include this information.

As explained in the file ide-cd, ATAPI CD-ROMS should be jumpered as "single" or "master", and not "slave" when only one IDE device is attached to an interface (although this restriction is no longer enforced with recent kernels).

4.2. Configuring and Building the Kernel

When initially installing Linux from CD-ROM you will likely be using a boot and/or root disk provided as part of a Linux distribution. If possible, you should choose a boot disk with the kernel driver for your CD-ROM device type. If you cannot find a boot disk with the necessary CD-ROM driver, you have several options:

1. Boot directly from CD-ROM (if supported by your computer and Linux CD)

2. Install over a network

3. Boot DOS, and install the Linux files onto your hard disk

4. Boot DOS, and create a set of floppies to install Linux

5. Find someone who can build you a boot disk with the needed CD-ROM driver

Once Linux has initially been installed, most users will want to compile their own kernel, usually for one of these reasons:

• to support a CD-ROM drive or other hardware

• to upgrade to a newer kernel release

• to free up memory resources by minimizing the size of the kernel

Obviously, you need to compile in support for your CD-ROM drive when you configure the kernel.

If you have an ATAPI CD-ROM drive, you need to enable Enhanced IDE/MFM/RLL disk/cdrom/tape support and Include IDE/ATAPI CDROM support.

For SCSI CD-ROM drives, enable the options SCSI support and SCSI CDROM support. Also enable support for your SCSI host adapter when prompted, e.g. Adaptec AHA152X/2825 support.

For proprietary interface CD-ROM drives, enable the appropriate driver. You can use the table listed previously to determine the driver to use for your model.

Virtually all CD-ROMs use the ISO-9660 file system, so you must also enable ISO 9660 CDROM filesystem support.

Although not needed for CD-ROM operation, if you have a sound card that is supported under Linux you might want to enable and configure the kernel sound driver at this time as well. The Sound HOWTO can be a useful reference here.

You should then follow the usual procedure for building the kernel and installing it. Don't boot with the new kernel until you create the device files and set up any boot time parameters as described in the next section.

The ISO-9660 filesystem and almost all of the CD-ROM drivers can be built as loadable kernel modules. This scheme allows the kernel drivers to be loaded and unloaded without rebooting the kernel, freeing up memory. I recommend you get your CD-ROM installation running using compiled-in drivers first. How to use modules is described in the modules documentation and the Kernel HOWTO.

If a drive type listed here is not supported by your kernel, you likely need to upgrade to a newer version.

It is possible that you need to use a driver that is distributed separately from the kernel source code. This usually involves patching the kernel. Again, the Kernel HOWTO explains how to do this.

Note that you can configure the kernel using the text-based program using "make config", a menu-based kernel configuration program invoked by "make menuconfig" and an X11-based graphical configuration invoked as "make xconfig". All three configuration methods offer on-line help.

4.3. Creating Device Files and Setting Boot Time Parameters

The kernel uses device files to identify which device driver to use. If you are running a standard Linux distribution you may have created the necessary device files during installation. Under Slackware Linux, for example, there is a menu-based setup tool that includes CD-ROM setup, and most systems have a /dev/MAKEDEV script. If you don't use these methods, you can use the more manual procedure listed in this section. Even if you use either of these methods, it is recommended that you at least verify the device files against the information in this section.

If you are using the new devfs file system in the 2.4 kernels, the device files are created dynamically by the kernel rather than residing on disk, and follow a different naming convention. The examples in this document assume that devfs is not being used, and may need to be adjusted accordingly if you are.

You create the device file by running the shell commands indicated for your drive type. This should be done as user root. Note that some Linux distributions may use slightly different CD-ROM device names from those listed here.

I recommended that you also create a symbolic link to the CD-ROM device to make it easier to remember. For example, for an IDE CD-ROM drive that is the second device on the secondary interface, the link would be created using

# ln -s /dev/hdd /dev/cdrom

If you want to play audio CDs, you will need to set the protection on the device file (the real file, not the symbolic link to it) to allow all users to read, e.g.

# chmod 664 /dev/hdd
# ls -l /dev/hdd
brw-rw-r--   1 root     disk      22,  64 Feb  4  1995 /dev/hdd

Some Linux distributions use group permissions to control access to devices such as CD-ROMs. A common convention is to only allow members of a group called cdrom to have access. In this case you should add the appropriate users to the group rather than changing file permissions on the device file.

When booting Linux, the device drivers attempt to determine whether the appropriate devices are present, typically by probing specific addresses. Many of the drivers auto-probe at several addresses, but because of differences in configuration, possible device conflicts, and hardware limitations, the drivers sometimes need help identifying the addresses and other parameters. Most drivers support an option on the kernel command line to pass this information to the device driver. This can be done interactively, or more commonly, configured into your boot loader. With LILO, for example, you would add an append command such as the following to your /etc/lilo.conf file:

append = "sbpcd=0x230,SoundBlaster"

See the LILO documentation for more information.

In the next section I discuss issues specific to individual device drivers, including device files, boot parameters, and the capabilities of the different drivers. You probably only need to read the section relevant to your drive type. The documentation files are usually found in the directory /usr/src/linux/Documentation/cdrom.

sbpcd=<io-address>,<interface-type>

# mknod /dev/sbpcd b 25 0

sonycd535=<io-address>

# mknod /dev/sonycd535 b 24 0

cdu31a=<io-address>,<interrupt>,PAS

cdu31a_port=<io-address> cdu31a_irq=<interrupt>

# mknod /dev/cdu31a b 15 0

aztcd=<io-address>

# mknod /dev/aztcd0 b 29 0

gscd=<io-address>

# mknod /dev/gscd0 b 16 0

mcd=<io-address>,<irq>

# mknod /dev/mcd b 23 0

mcdx=<io-address>,<irq>

# mknod /dev/mcdx0 b 20 0

cm206=<io-address>,<interrupt>

# mknod /dev/cm206cd b 32 0

optcd=<io-address>

# mknod /dev/optcd0 b 17 0

sjcd=<io-address>,<interrupt>,<dma>

# mknod /dev/sjcd b 18 0

# mknod /dev/pcd0 b 46 0

# mknod /dev/scd0 b 11 0
# mknod /dev/scd1 b 11 1

hdx=cyls,heads,sects,wpcom,irq
  or
hdx=cdrom

4.4. Booting the Linux Kernel

You can now reboot with the new kernel. Watch for a message such as the following indicating that the CD-ROM has been found by the device driver (the message will vary depending on the drive type):

hdd: TOSHIBA CD-ROM XM-7002B, ATAPI CD/DVD-ROM drive

If the bootup messages scroll by too quickly to read, you should be able to retrieve them using dmesg or tail /var/log/messages.

If the drive is not found, then a problem has occurred, See the section on troubleshooting.

4.5. Mounting, Unmounting, and Ejecting Devices

To mount a CD-ROM, insert a disc in the drive, and run the mount command as root (this assumes you created a symbolic link to your device file as recommended above and that an empty directory /mnt/cdrom exists):

# mount -t iso9660 -r /dev/cdrom /mnt/cdrom

The CD can now be accessed under the directory /mnt/cdrom.

There are other options to the mount command that you may wish to use; see the mount(8) man page for details.

You can add an entry to /etc/fstab to automatically mount a CD-ROM when Linux boots or to specify parameters to use when it is mounted; see the fstab(5) man page.

Note that to play audio CDs you should not try to mount them.

To unmount a CD-ROM, use the umount command as root:

# umount /mnt/cdrom

The disc can only be unmounted if no processes are currently accessing the drive (including having their default directory set to the mounted drive). You can then eject the disc. Most drives have an eject button; there is also a standalone eject program that allows ejecting CD-ROMs under software control.

Note that you should not eject a disc while it is mounted (this may or may not be possible depending on the type of drive). Some CD-ROM drivers can automatically eject a CD-ROM when it is unmounted and insert the CD tray when a disc is mounted (you can turn this feature off when compiling the kernel or by using a software command).

Its possible that after playing an audio CD you may not be able to mount a CD-ROM. You need to send a CD audio "stop" command (using a CD player program) before trying the mount. This problem only appears to occur with the SBPCD driver.

Recent kernels support a kernel-based automounter which provides transparent mounting of removable media including CD-ROM. You can find the tools needed to use it at ftp://ftp.kernel.org/pub/linux/daemons/autofs/.

4.6. Troubleshooting

If you still encounter problems after following the instructions in the HOWTO, here are some things to check. The checks are listed in increasing order of complexity. If a check fails, solve the problem before moving to the next stage.

% uname -a
Linux moe 2.4.4 #1 Sat Apr 28 10:30:45 EDT 2001 i686 unknown  

% cat /proc/version
Linux version 2.4.4 (root@moe) (gcc version 2.95.2 20000220 (Debian GNU/Linux)) #1 Sat Apr 28 10:30:45 EDT 2001

% cat /proc/devices
Character devices:
 1 mem
 2 pty
 3 ttyp
 4 ttyS
 5 cua
 7 vcs

Block devices:
 3 ide0
22 ide1

% cat /proc/filesystems
        ext2
nodev   proc
nodev   devpts
        vfat
        iso9660

howto % cat /proc/ioports
 ...
0230-0233 : sbpcd
 ...

% dmesg

% tail /var/log/messages

# dd if=/dev/cdrom of=/dev/null bs=2048
^C
124+0 records in
124+0 records out

% dmesg
SBPCD: sbpcd_open: no disk in drive

5.1. Audio CD Players

Several programs are available for playing audio CDs, either through a headphone jack or an attached sound card.

Some of these programs are coded to use a specific device file for the CD-ROM (e.g. /dev/cdrom). You may be able to pass the correct device name as a parameter, or you can create a symbolic link in the /dev directory. If sending the CD output to a sound card, you may wish to use a mixer program to set volume settings or select the CD-ROM input for recording.

5.2. PhotoCD

PhotoCDs use an ISO-9660 file system containing image files in a proprietary format. Not all CD-ROM drives support reading PhotoCDs.

The hpcdtoppm program by Hadmut Danisch converts PhotoCD files to the portable pixmap format. It can be obtained from ftp://ftp.gwdg.de/pub/linux/hpcdtoppm or as part of the PBM (portable bit map) utilities, available on many archive sites (look for "pbm" or "netpbm").

The photocd program by Gerd Knorr (kraxel@cs.tu-berlin.de) can convert PhotoCD images into Targa or Windows and OS/2 bitmap files.

The same author has written the program xpcd, an X11-based program for handling PhotoCD images. You can select the images with a mouse, preview the image in a small window, and load the image with any of the five possible resolutions. You can also mark a part of the Image and load only the selected part. Look for these packages at ftp://ftp.cs.tu-berlin.de/pub/linux/Local/misc/.

The ImageMagick image file manipulation program also supports PhotoCD files. It is available from ftp://ftp.x.org/contrib/applications/ImageMagick/.

5.3. Mkisofs

Eric Youngdale's mkisofs package allows creating an ISO-9660 file system on a hard disk partition. This can then be used to assist in creating and testing CD-ROM file systems before mastering discs.

5.4. ISO-9660 Utilities

These are some utilities for verifying the format of ISO-9660 formatted discs; you may find them useful for testing suspect CDs. The package can be found at ftp://ftp.cdrom.com/pub/unixfreeware/archive/. They were written by Bill Siegmund and Rich Morin.

6.1. How can a non-root user mount and unmount discs?

Most mount commands support the user option. If you make an entry such as the following in /etc/fstab:

/dev/sbpcd  /mnt/cdrom   iso9660     user,noauto,ro

then an ordinary user will be allowed to mount and unmount the drive using these commands:

% mount /mnt/cdrom
% umount /mnt/cdrom

By default the disc will be mounted with some options that help enforce security (e.g. programs cannot executed, device files are ignored). If this is too restrictive you can use additional options (e.g. the "exec" option will enable execution or programs). See the mount(8) man page for details.

Another method is to get the usermount package which allows non-root users to mount and unmount removable devices such as floppies and CD-ROMs, but restricts access to other devices (such as hard disk partitions). It is available on major archive sites.

Yet another option is to use the sudo program which allows users to run selective programs with root privileges.

6.2. Why do I get device is busy when unmounting a CD-ROM?

The disc cannot be unmounted if any processes are accessing the drive, including having their default directory set to the mounted filesystem. If you cannot identify the processes using the disc, you can use the fuser command, as shown in the following example.

% umount /cdrom
umount: /dev/hdd: device is busy
% fuser -v /cdrom
                     USER       PID ACCESS COMMAND
/mnt/cdrom           tranter    133 ..c..  bash

On some systems you may need to be root when running the fuser command in order to see the processes of other users.

6.3. How do I export a CD-ROM to other hosts over NFS?

You need to add an entry to the /etc/exports file. Users on other machines will then be able to mount the device. See the exports(5) man page for details.

6.4. Can I boot Linux from a CD-ROM?

Most Linux distributions support directly booting a Linux kernel from CD as an alternative to a boot floppy. This requires a bootable CD and ROM BIOS and CD-ROM drive which supporting booting from CD.

The latest version of mkisofs supports creating such disks using the El Torito standard for bootable CDs.

6.5. How can I read digital data from audio CDs?

Heiko Eissfeldt (heiko@colossus.escape.de) and Olaf Kindel have written a utility that reads audio data and saves it as .wav format sound files. The package is called cdda2wav.tar.gz and can be found on www.ibiblio.org.

Another utility to extract digital audio is cdparanoia available from http://www.xiph.org/paranoia.

Because CD-ROM drives are changing very quickly, it is difficult to list which models support reading digital data. Your best bet is to get the latest cdda2wav or cdparanoia package and read the documentation.

For more information on this subject, see the web site http://www.tardis.ed.ac.uk/~psyche/cdda/ and the alt.cd-rom FAQ listed in the references section.

6.6. Why doesn't the find command work properly?

On ISO-9660 formatted discs without the Rock Ridge Extensions, you need to add the -noleaf option to the find command. See the find(1) man page for details.

(In my experience virtually all recent Linux CDs use the Rock Ridge extensions, so this problem should occur very rarely.)

6.7. Does Linux support any recordable CD-ROM drives?

Linux supports most CD-R and CD-RW drives. The cdrecord and mkisofs tools can be used to burn CDs, there are also many graphical front-ends to these tools. For more information see the Linux CD-Writing HOWTO.

6.8. Why do I get mount: Read-only file system when mounting a CD-ROM?

CD-ROM is a read-only media. With some early kernels you could mount a CD-ROM for read/write; attempts to write data to the CD would simple be ignored. As of kernel version 1.1.33 this was corrected so that CD-ROMs must be mounted read only (e.g. using the -r option to mount).

6.9. Why does the disc tray open when I shut down the system?

The sbpcd driver supports automatically ejecting the CD when it is unmounted. In some older kernel versions this was the default behaviour. If you shut down the system, a mounted CD will be unmounted, causing it to eject.

This feature is for convenience when changing discs. If the tray is open when you mount or read a CD, it will also automatically be closed.

I found that this caused problems with a few programs (e.g. cdplay and workbone). As of the 1.1.60 kernel you can control this feature under software control. A sample program is included in the sbpcd documentation file (or use the eject program). You can also control the default behaviour by editing the kernel source file sbpcd.h.

6.10. I have a "special" CD that can't be mounted

If you have a particular disc that cannot be mounted, here are some possible reasons:

1. It is an XA, CD-R, or CD-RW disc and your drive or the Linux driver does not support reading these discs (this is only likely for very old drives).

2. It is a DVD disc, which is only readable by a DVD-ROM drive.

3. The disc doesn't use an ISO-9660 file system (e.g. some use SunOS or HFS).

4. It is an audio CD.

5. The CD is damaged or defective.

6. You put it in the drive upside down :-)

6.11. Do multi-platter CD-ROM drives work with Linux?

Several users have reported success with SCSI multi-disc CD-ROM changers. You probably need to enable the "Probe all LUNs on each SCSI device" kernel configuration option (this is not necessary if your CD changer is already known to the SCSI-driver. Have a look at /usr/src/linux/drivers/scsi.c).

At least one user also had to increase a SCSI timeout value in the kernel driver. A symptom of this is an error message like "wrong fs type, bad option, bad superblock on /dev/sr5, or too many mounted file systems" when trying to mount a CD for the first time, but a second mount immediately afterwards succeeds. To increase the timeout increase the value of IOCTL_TIMEOUT at the beginning of /usr/src/linux/drivers/scsi/sr_ioctl.c and recompile the kernel. A value of 10000 instead of the default 3000 is reported to work with a NEC Multispin 4Xc.

It might be necessary to create additional block special files, so that all LUNs can be accessed. A device file is needed for every LUN. So for a 7 disc changer /dev/sr0 to /dev/sr6 are needed (more if you have additional SCSI CD-ROM drives). To create the block special file execute mknod /dev/sr? b 11 ? as root with ? being the required number.

The Nakamichi MBR-7 7 disc changer, NEC Multispin 4Xc and Pioneer 12 disc changer have been reported to work.

EIDE/ATAPI multi-disc changers are also available. The kernel has support for some drives using the CDROM_SELECT_DISC ioctl function. The IDE-CD kernel driver documentation file includes source code for a program to select changer slots, or you can use various utilities such as the eject program described earlier.

6.12. I get "/cdrom: Permission denied" errors

Some CDs have root directory file permissions that only allow user root to read them. This is an error on the part of the CD-ROM vendor and is a real inconvenience. A more common occurrence is for certain files or directories not to be world readable. Some people have patched their kernels to work around the problem.

Also see the related question on hidden files later in this document.

6.13. How do I interpret IDE CD kernel error messages?

What does it mean when I get a kernel message from the IDE CD-ROM driver like "hdxx: code: xx key: x asc: xx ascq: x"?

This is an status/error message from the IDE CD-ROM drive. By default the IDECD driver prints out the raw information instead of wasting kernel space with error messages. You can change the default to display the actual error messages by going into /usr/src/linux/drivers/block/ide-cd.c, changing the value of VERBOSE_IDE_CD_ERRORS to 1, and recompiling the kernel.

6.14. How can I tell what speed CD-ROM I have?

Here's one way. This command measures how long is takes to read 1500K of data from CD:

% time -p dd if=/dev/cdrom of=/dev/null bs=1k count=1500
1500+0 records in
1500+0 records out
real 5.24
user 0.03
sys 5.07

The transfer rate of single speed drives is 150 kilobytes per second, which should take about 10 seconds. At double speed it would take five seconds, quad speed would take 2.5, etc.

The "real" time above is probably the best number to look at -- in this case it indicates a double speed drive. You can increase the amount of data transferred to get a more accurate value (the data does not get cached). You should probably run the command a few times and take the average.

I've also written a small C program that measures and reports CD-ROM data transfer rate; I can send it to you on request.

6.15. My CD-ROM stopped working after Linux was installed

The usual symptom is that the boot disk used to initially install Linux recognized your CD-ROM drive, but after Linux was installed on the hard drive or floppy and rebooted it no longer recognizes the CD-ROM.

The most common reason for this problem is that with some Linux distributions the kernel that is installed on your hard drive (or floppy) is not necessarily the same one that was on your boot disk. You selected a boot disk that matched your CD-ROM hardware, while the kernel you installed is a "generic" kernel that is lacking CD-ROM support. You can verify this by following the troubleshooting guidelines discussed previously in this document (e.g. start by checking /proc/devices).

The solution is to recompile the kernel, ensuring that the drivers for your CD-ROM drive and any others that are needed (e.g. SCSI controller, ISO-9660 file system) are included. See the Kernel HOWTO if you don't know how to do this.

If you passed any command line options to the boot disk (e.g. "hdc=cdrom") you need to add these to your boot program configuration file (typically /etc/lilo.conf).

6.16. There are "hidden" files on a CD which I can't read

Some CDs have files with the "hidden" bit set on them. Normally these files are not visible. If you mount the CD with the "unhide" option then the files should be accessible (this doesn't seem to be documented anywhere).

6.17. Where is the CD-ROM API documented?

If you want to write your own application, such as an audio CD player program, you will need to understand the application programming interface (API) provided by Linux.

Originally the CD-ROM kernel drivers used their own ioctl() functions to support features specific to each drive. Header files such as /usr/include/linux/sbpcd.h describe these. Because many of the drivers were based on other drivers, the interfaces, while not identical, have a lot in common.

More recently there has been an initiative headed by David van Leeuwen (david@tm.tno.nl) to standardize the API for CD-ROM drives, putting common code in one place and ensuring that all drivers exhibit the same behaviour. This is documented in the file /usr/src/linux/Documentation/cdrom/cdrom-standard.tex. Several kernel drivers support this. As of the 2.0 kernel all CD-ROM drivers conform to this API.

My book, Linux Multimedia Guide, goes into quite a bit of detail on how to program CD-ROM drives, especially for audio functions. See the end of the References section.

6.18. Why don't I see long filenames on this Windows CD-ROM?

If you have a CD-ROM which has long filenames under Windows but not under Linux, it may be formatted using Microsoft's proprietary Joliet filesystem. See the next question for a solution.

6.19. Is Microsoft's Joliet filesystem supported?

Microsoft has created an extension to the ISO CD-ROM format called Joliet. It allows for long filenames encoded using the 16-bit UNICODE format.

Starting with version 2.0.34 the Linux kernel has support for the Microsoft Joliet file system extensions. You need to enable support for it in the kernel.

If you want to display filenames with native language characters from Joliet CD-ROMs correctly on the screen, you need to enable support in the kernel for the appropriate NLS ISO8859 character sets.

6.20. Does Linux support "enhanced" CDs?

Some audio CDs are "enhanced" with additional data. Typically you will find that these CDs have the usual audio CD tracks as well as a data track which can be mounted as an ISO-9660 file system.

An enhanced CD I examined had Microsoft Windows and Apple Macintosh applications on it (which won't run directly under Linux of course, although I had partial success running the Windows application under the WINE Windows emulator). There were some GIF images which could be viewed using a standard viewer such as xv and some animations in Apple QuickTime format which could be viewed using the xanim program. It was a multi-session disk which some very old CD-ROM drives do not support reading. On the disc was a readme.txt file containing an Enhanced CD FAQ.

6.21. Does Linux support DVD-ROM?

SCSI and ATAPI compliant DVD-ROM drives should work under Linux for reading discs formatted with an ISO-9660 file system. In other words they will work as a (possibly large) CD-ROM drive.

Many DVD-ROM discs use the UDF file system. Recent kernels have UDF filesystem support.

A number of Linux MPEG-2 DVD players are available. For more information see the DVD Playing HOWTO.

6.22. Does Linux support CD-RW?

SCSI and ATAPI compliant CD-RW drives work under Linux for discs formatted with an ISO-9660 or UDF file system. This includes the ability to write to the disc. Utilities such as cdrecord can be used to erase a disc.

6.23. How do I mount a multi-session disc?

You mount a multi-session disc like any other CD-ROM. The normal behaviour for multi-session support is that the last session will be seen when you mount the disc. You will not see multiple partitions. If it does not work it could be for three reasons:

1. Your CD-ROM drive does not support reading multi-session CDs (it would probably have to be quite old for this to be the case).

2. The Linux kernel driver for your CD-ROM type does not support multi-session (mostly only some old proprietary, non-IDE/ATAPI and non-SCSI drives fall into this category).

3. If you are mounting a CD with a file system other than ISO-9660, then multi-session may not be supported.

6.24. How do I read a CD volume label?

There is a small utility called volname included with recent versions of the eject program. Alternatively you can run this shell command:

dd if=/dev/cdrom bs=1 skip=32808 count=32 

assuming /dev/cdrom is the device file name for your drive.

6.25. My IDE CD-R or CD-RW drive is not working with Linux

You need to use the IDE SCSI emulation driver for writable drives. See the Linux CD-Writing HOWTO for more information.

6.26. Is the insert your brand/model here IDE CD-ROM drive supported?

Yes, of course it is. Linux supports the IDE interface used by all modern IDE CD-ROM drives. It has been like this since kernel version 1.1.85.

6.27. I can't seem to find a driver for my IDE drive in the kernel source?

Unlike for the older proprietary drives, there isn't a specific driver for each model of ATAPI/IDE CD-ROM drives. All drives conforming to the standard should work with the ATAPI CD-ROM driver included in the standard Linux kernel.

6.28. I'm having problems with my CD-ROM on Red Hat 7.1

You may be running into an issue with hardware that does not support DMA (Direct Memory Access). RedHat ships a highly tuned version of the Linux kernel which enables DMA on selected IDE controller chipsets. Information on this issue can be found at http://www.exocore.com/linux/rhl71dma/