This page summarizes a few observations about writing ("burning") CD and DVD media under Linux.
Note: The material on this page is no longer updated. I keep this page merely as reference material: With a recent Linux distribution, burning CD and DVD is easy and straightforward.
If you use your computer for serious work, the price of lost data is certainly more expensive than any backup medium. That's why I perform regular backups onto CD-RW media (see below) and from time to time I archive my complete /home directory tree onto CD-R. The media are nowadays really cheap (you can find quality CD-R for 0.50 CHF). If I have less than 650 MB to save, I use multi-session CDs and add several sessions onto the same disk, but in different directories. First, create an ISO image:
mkisofs -L -J -R -V Backup_Home -m '*cache*' -o /tmp/img.iso -graft-points home.20010704/=/home
The trick for differentiating backups from different dates lies in the
-graft-points. I use this to relocate the directory
/home to the new directory home.20010704 on the CD -
the extension after the dot is the date when the backup was performed,
here it is the 4th of July 2001.
The other options stem from practical considerations:
preserves file ownership and permissions,
-J enables the
Joliet filesystem, so that all filenames are readable on Linux
and MS-DOS systems.
-L allows filenames with a leading dot
(think hidden files ;-) and
-V is followed by the volume name.
-o gives the name of the output file (here, /tmp/img.iso),
-m excludes cache files - I do not need a backup of that.
Make sure you use
mkisofs 1.13 or later. The earlier versions
had problems with multi-session disks. -- For 650-MB CD media, don't let
the image file to grow bigger than 332500 blocks (each 2048 bytes, makes
680960000 bytes in total). Some CD-writing programs and/or CD-R disks
don't allow bigger images. Then, burn the disk using the option
-multi for a multi-session disk:
cdrecord -v -multi -pad speed=6 dev=0,6,0 /tmp/img.iso
When the next backup is due, we need to recover the information of the
previous session. This is done by inserting the CD and launching
with the options
-M (see the manpage for details):
mkisofs -L -J -R -V Backup_Home -C `cdrecord dev=0,6,0 -msinfo` -M /dev/scd0 -m '*cache*' -o /tmp/img.iso -graft-points home.20010710/=/home
mkisoifs will report the size of the final data, including
the first session. Verify that it fits on the CD, then burn the disk with the
same command as above. If this is the last session on the disk, close the disk
by simply omitting the
-multi option from cdrecord:
cdrecord -v -pad speed=6 dev=0,6,0 /tmp/img.iso
If you mount this disk in /cdrom, you will see two directories, /cdrom/home.20010704 and /cdrom/home.20010710, holding the data from the different backups.
Note that there is a certain risk if you use multisession CD-R as your only backup medium: If, for any reason, writing the CD fails, all data on that CD are gone. So, use at least two independent techniques for backup, and verify that you are able to restore your data.
Note also that
mkisofs does not follow symbolic links. If you have a symlink
called /home/audio that points to /mnt/audio, these data will not be included!
Besides the "permanent" backup to tape and/or CD-R media, I use CD-RW to perform quick, systematic backups of the most important system directories, such as /home, /root, /etc and /var.
The script saveset.sh meets several of my requirements: It allows inclusion and exclusion based on patterns, verifies that the data fit on a single CD and that enough disk space for the temporary file exists, it uses relocation to avoid merging of directories, and it preserves access rights. The script also allows to read an external configuration file, e.g. to use with multiple data sets or multiple CD-RW devices. - This script has also been the subject of an article on the Pro-Linux site, written by Hendric Stattmann (in German) and has been extended for use with a DVD writer by the same author.
Download the saveset.sh script. Instructions for configuration are in the file.
Download the saveset-dvd.sh script. Instructions for configuration are in the file.
If you are sure that you regularly exceed the capacity of one disk,
you might be interested in the
cdtape script below.
The script cdtape lets you use a CD-RW
drive similar to a tape drive. It actually is a filter, redirecting the output
from your favourite archive/compression/whatever utility to
A few usage examples:
To save a directory to CD:
tar cf - /DirectoryToBeSaved | cdtape save
To obtain a listing of the archive:
cdtape restore | tar tvf -
To extract a certain file from the archive:
cdtape restore | tar xvf - FileToRestore
To copy an audio CD which does not have the traditional
two seconds of pause between tracks (which is often the case with
cdrdao is the software of choice. To copy an
audio CD "1:1", first run
cdrdao read-cd --device 0,5,0 --paranoia-mode 3 audio-cd.toc
which writes a binary image file data.bin into the current directory, correcting any scratches or errors as far as possible. To write this image back onto a fresh CD, use
cdrdao write --device 0,6,0 --eject audio-cd.toc
If you want to do a test run before burning, add
Note that the filesize reported here is not strictly correct as the CD is
written in audio format - what counts is the number of blocks writte and this
should not exceed 332500.
Recent versions of
cdrdao have this functionality built in:
cdrdao copy --source-device ATA:1,1,0 --device ATA:1,0,0 --buffers 64
So what is the "best" way to copy a data CD?
The problem lies in the extraction of the "raw" data as an ISO image from the CD. Inspired by an article from Steve Litt, I took the first disk from my SuSE Linux 7.3 and ran a number of different commands on this disk.
First of all, some statistics from
isoinfo -d -i /dev/scd0:
CD-ROM is in ISO 9660 format System id: LINUX Volume id: SU7300.001 [snip] Volume set size is: 1 Volume set seqence number is: 1 Logical block size is: 2048 Volume size is: 330704 Joliet with UCS level 3 found Rock Ridge signatures version 1 found
The output of
isosize -x /dev/scd0 is coherent with this:
sector count: 330704, sector size: 2048
Then I ran a few different commands that are frequently used to copy disks:
temp/iso> cat /dev/scd0 > ./img_cat.iso temp/iso> dd if=/dev/scd0 of=./img_dd_bare.iso 1323416+0 records in 1323416+0 records out temp/iso> dd if=/dev/scd0 of=./img_dd_bare_corr.iso conv=notrunc,noerror 1323416+0 records in 1323416+0 records out temp/iso> dd if=/dev/scd0 of=./img_dd_bs.iso bs=2048 330854+0 records in 330854+0 records out temp/iso> dd if=/dev/scd0 of=./img_dd_count_corr.iso bs=2048 count=330704 conv=notrunc,noerror 330704+0 records in 330704+0 records out temp/iso> dd if=/dev/scd0 of=./img_dd_count_nocorr.iso bs=2048 count=330704 330704+0 records in 330704+0 records out
Up to this point, all six techniques seem to work fine. But then, a look at the file size (here: in blocks of 2k) reveals a surprise:
temp/iso> ls -s -1 --block-size=2048 total 1655600 331180 img_cat.iso 331180 img_dd_bare.iso 331180 img_dd_bare_corr.iso 331180 img_dd_bs.iso 331030 img_dd_count_corr.iso 331030 img_dd_count_nocorr.iso
None of these files is 330704 2k-blocks in size and there is a difference of
150 blocks (of 2048 bytes each) between the "raw" files and the two files
generated using the
A comparison all files to the CD-ROM (
diff -r $file /dev/scd0
as well as the checksums generated with
md5sum show that the latter
two files differ from the original CD-ROM (first line):
993b97cd78ce73ac37f5ac8db50824f5 /dev/scd0 993b97cd78ce73ac37f5ac8db50824f5 img_cat.iso 993b97cd78ce73ac37f5ac8db50824f5 img_dd_bare.iso 993b97cd78ce73ac37f5ac8db50824f5 img_dd_bare_corr.iso 993b97cd78ce73ac37f5ac8db50824f5 img_dd_bs.iso 8acfbbfac2b4bdb8113d774ca29b7d5e img_dd_count_corr.iso 8acfbbfac2b4bdb8113d774ca29b7d5e img_dd_count_nocorr.iso
It gets even more surprising: The data reported by
isoinfo -d -i $file
isosize -x $file do not refer to the complete file but are only the
header information! If you don't believe this, then just run
one of the two programs on the ISO file while the CD is being
extracted, i.e. when the image file is guaranteed not to be complete.
The size reported will always be that of the "theoretical" file ... !
Thus, my recommendation to copy a data CD "1:1" is as follows:
cator - probably better? -
ddon the device, without specifying the block count. It does not matter if the disc is mounted or not.
cdrecord -v -pad speed=6 dev=0,6,0 /tmp/img.iso).
(Note: For the following discussion I assume that "Mixed Mode" is identical with "CD+" (CDplus), i.e. Music tracks with added data. Please correct me if I'm wrong!)
You cannot just write audio and data tracks "mixed" on a CD-R, as (1) an audio CD-Player will identify one more audio track than there are (it's the data track) and (2) the data track is no longer accessible. It is there, but the CD cannot be mounted, neither under Linux nor under Windows! So, here's how to do it:
First, write your audio files onto a multi-session disk:
cdrecord -multi -pad speed=6 dev=0,6,0 -audio *.wav
Then, retrieve the multi session info:
cdrecord dev=0,6,0 -msinfo
This will print the session start positions of the last and the next session, generally something like "0,121550". Now, create an ISO filesystem with the data files that includes the above "offset" for the multi-session audio part:
mkisofs -R -J -o /tmp/fs.iso -C 0,121550 temp/
In this example, the ISO image will be created in /tmp and we
read the data files from a directory "temp" which is located below
the actual working directory. We specify
to obtain a CD that is readable both under Linux and MS-Windows.
mkisofs will issue a warning that option
not specified, however, we don't need this feature here - just ignore the
The final size reported in the mkisofs output is that of the complete
CD, including the audio tracks we recorded before. Note that you cannot
"dry-run" mkisofs with the option
-print-size in this mode;
it will report a wrong size.
Next, burn the image onto the CD. We do not specify "multi" here as we will close the CD:
cdrecord -pad speed=6 dev=0,6,0 -v -data /tmp/fs.iso
... and you're done. This CD can be played in an audio CD player and be read as a normal data CD in your computer. I could not find any difference between a CD made this way and a commercial CD+ (well, the only one I have ;-).
(Based on Jörg Schilling's pages around cdrecord).
To create a bootable ISO9660 cdrom image file with Joliet and Rock Ridge support, change directory to the place that will be the root directory of the cd. Then:
mkisofs -v -J -r -T \ -b images/boot.img \ (boot image) -c boot.catalog \ (boot catalog, will be created by mkisofs) -p My_Name \ (Preparer, <128 characters, optional) -A My_boot_CD \ (Application ID, <128 characters, optional) -V Linuxboot \ (CD ID, optional but recommended) -o /tmp/img.iso . (ISO image to be written)
Then, test your new disk image by mounting it. If you forgot to fix file permissions or set the rock ridge extensions then the error will be obvious here since the file names and directory structure will be wrong:
mount -t iso9660 -o ro,loop=/dev/loop0 /tmp/img.iso /cdrom
When you're done, unmount it and burn the disk.
(I captured this somewhere on Internet but I admit I have lost the source!
See also Martin L. Purschkes page about creating your own rescue CD.)
Note: This section is nowadays obsolete since all recent Linux distributions can handle such drives "out of the box". However, I'm leaving this information online for reference purposes.
CD-R and CD-RW drives with SCSI are supported natively by Linux. Using an IDE (ATAPI) CD-RW is not difficult either:
cdrecord dev=/dev/hdc ...).
ide-scsidriver. In the bootloader configuration (/etc/lilo.conf or /boot/grub/menu.lst), go to the section that boots the Linux kernel. Add the option
hdcby the letter that corresponds to your CD-writer). The CD recorder should show up as device "0,0,0" (
cdrecord dev=0,0,0 ...).
In case you are using Kernel 2.4, the latter procedure also works if you use a "real" SCSI adapter together with an ATAPI-CD-writer. In /etc/init.d/boot.local, add a second line that may look like this:
/sbin/modprobe ide-scsi /sbin/modprobe aic7xxx
In this example, the second line loads the kernel module for an
Adaptec 2940 card after the
ide_scsi module. -
In such a system, the IDE-SCSI device will show up as host
and the "real" SCSI adapter will appear as
scsi1. Here is the
cat /proc/scsi/scsi on a system that uses IDE harddisks,
an IDE CD-RW plus a SCSI tape:
Attached devices: Host: scsi0 Channel: 00 Id: 00 Lun: 00 Vendor: PLEXTOR Model: CD-R PX-W1610A Rev: 1.03 Type: CD-ROM ANSI SCSI revision: 02 Host: scsi1 Channel: 00 Id: 03 Lun: 00 Vendor: Quantum Model: DLT4000 Rev: CC37 Type: Sequential-Access ANSI SCSI revision: 02