How to use your CD-ROM under Linux
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He is a Linux fan besides working in a campus network center. Hobbies:hamradio,
swimming. Using Linux as a normal user for one year, doing system administration
on Linux/Unix for another year. Finishing the graduate thesis on billing
systems with a Linux based proxy server.
This article gives a short but useful description on how to use your CD-ROM under Linux. It describes how to find the CD-ROM device, mount (make available) the CD-ROM,
read the contents, umount it and gives some hints for troubleshooting.
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Find out what the name of your CD-ROM device is
You got you Linux-box to work, now you want to copy a file from a CD-ROM
to your hard disk.
Check if the CD-ROM device was identified correctly by the Linux kernel
using the command dmesg.
If you have an ATAPI cdrom connected via IDE then this might look like:
|$ dmesg |more
hda: QUANTUM FIREBALL CR8.4A, ATA DISK drive
hdc: CD-ROM CDU701, ATAPI CDROM drive
ide0 at 0x1f0-0x1f7,0x3f6 on irq 14
ide1 at 0x170-0x177,0x376 on irq 15
hda: QUANTUM FIREBALL CR8.4A, 8063MB w/418kB Cache, CHS=16383/16/63,
hdc: ATAPI 14X CD-ROM drive, 128kB Cache
Uniform CDROM driver Revision: 2.55
If you have an SCSI cdrom then it might look like:
|$ dmesg |more
Detected SCSI removable disk sdc at scsi0, channel 0, id 5, lun 0
Vendor: PLEXTOR Model: CD-ROM PX-12TS Rev: 1.03
Type: CD-ROM ANSI SCSI revision: 02
Detected scsi CD-ROM sr0 at scsi0, channel 0, id 6, lun 0
scsi : detected 1 SCSI cdrom 3 SCSI disks total.
The 'hdc: CD-ROM CDU701, ATAPI CDROM drive' line tells
us that you have a CD-ROM IDE/ATAPI-CD drive attached on the computer.
Linux assign it a device name-'hdc' for access later on. The name of device
depends on the hardware type and it is hdc in the first case and
sdc in the case where you have SCSI CD-ROM.
Mount (make available) your CD-ROM
Generally you must be the super user (root) to do that, but in chapter
mounting a CD-ROM as normal user we will see how this can be done by
anybody (It is generally best to do as little as possible as user root).
Mounting is necessary before
you can read the contents on a CD-ROM disk. Insert a CD-ROM disk in your
CD-ROM, make sure the directory /cdrom exists and type command :
|#mount /dev/hdc -t iso9660 -r /cdrom
|in case of a scsi cd-rom this is
#mount /dev/sdc0 -t iso9660 -r /cdrom
The device name of the CD-ROM is the one that was shown
in the output of the dmesg command.
Accessing your CD-ROM
After the cdrom is mounted you can check with the
disk free command (df) that it is correctly mounted at the /cdrom directory:
Used Available Capacity Mounted on
/dev/sda1 2974519 1516768 1303931 54% /
/dev/sda3 2686158 2378788 153548 94% /home
/dev/hdc 603646 603646 0 100% /cdrom
Now you can now access your cd-rom like a normal directory at /cdrom.
Unmounting your CD-ROM
After finishing your work, you may want to take the CD-ROM out, but you find
that the push button at the CD-ROM drive front panel does no longer open
The CD-ROM is *locked*. You should first
unmount (the command is umount with out the n) the cdrom.
Try following command as super user (root):
or alternatively you can type
|In case of the scsi cd this is:
After that you can take it out by pushing the button on the drive front panel.
You can also use a program called eject to
open the cdrom drive via command.
Mounting and unmounting without being root
When you are logged in as root you can do anything but you
can also accidently do more than you wanted to. It is therefore better to
make the cdrom mountable for ordinary users. To give the privileges to
mount a drive to any user you must first log in as root and
do 3 things:
- make the directory /cdrom world writable
- make the device world writable
- edit the fstab
To make the directory /cdrom world writable you type (while no
cdrom is mounted!):
To make the device world writable you type (use the device name
as described in the first chapter):
|for the ATAPI cdrom:
#chmod 666 /dev/hdc
|for the SCSI cdrom:
#chmod 666 /dev/scd0
Now you must edit /etc/fstab and give the permission to mount
the cdrom to any user. This is done by inserting the line
Please note that there might already be a line for the /dev/hdc device
(or /dev/sdc0) in this case you have to edit the line and not add
a new entry. The line tells Linux on which directory to mount the
cdrom and with device to use. It tells Linux also that the file
system is iso9660, that it should be mounted read only and that it
should never be mounted at startup (when there might not be a CD
in the drive). The option "user" means that any user
can mount the drive.
/dev/hdc /cdrom iso9660 ro,noauto,user 0 0
In the case of the scsi cdrom this looks like:
/dev/sdc0 /cdrom iso9660 ro,noauto,user 0 0
Save the fstab file and log in as normal user. Now insert a CD
into the drive and mount it with the command:
Easy, isn't it?
It is now possible to use this short form because
Linux can get all the other parameters from /etc/fstab.
Be sure you are *not* in any directory below
the /cdrom directory tree; check if someone else is in one of the directory
of /cdrom. If you can't find out who is using it then it is probably
some background process of yours that is using the drive.
To find out which one, you can type /usr/sbin/fuser /cdrom
Terminate the process and you can umount + eject the CD.
You check the kernel message before you want to mount the CD-ROM for
getting the correct device name and its annoying you that you forget it
all the time. Here is
a solution: Create a soft link for your CD-ROM device:
Failed umount CD-ROM and got 'device is busy' message. (here we had
mounted CD-ROM previously at /cdrom )
#ln -s /dev/hdc /dev/cdrom
Now you can mount /dev/cdrom to /cdrom and forget if it is /dev/hdc
or /dev/hdb. (But look also at chapter
"Mounting/unmounting without being root"
which shows an
even better way to do this)
Look at chapter
"Mounting/unmounting without being root"
It is not necessary to mount a audio-cd. Try programs such as workbone
(for console) or workman and xplaycd (for X-win) if your CD-ROM
hardware has no play music buttons.
When typing umount /cdrom you get the message
umount: /cdrom is not in the fstab (and you are not root)