READCD(1) Schily's USER COMMANDS READCD(1)
readcd - read or write data Compact Discs
readcd [ dev=device ][ options ]
Readcd is used to read or write Compact Discs.
The device refers to scsibus/target/lun of the drive. Communication on SunOS is done with
the SCSI general driver scg. Other operating systems are using a library simulation of
this driver. Possible syntax is: dev= scsibus,target,lun or dev= target,lun. In the lat-
ter case, the drive has to be connected to the default SCSI bus of the machine. Scsibus,
target and lun are integer numbers. Some operating systems or SCSI transport implementa-
tions may require to specify a filename in addition. In this case the correct syntax for
the device is: dev= devicename:scsibus,target,lun or dev= devicename:target,lun. If the
name of the device node that has been specified on such a system refers to exactly one
SCSI device, a shorthand in the form dev= devicename:@ or dev= devicename:@,lun may be
used instead of dev= devicename:scsibus,target,lun.
To access remote SCSI devices, you need to prepend the SCSI device name by a remote device
indicator. The remote device indicator is either REMOTE:user@host: or REMOTE:host:
A valid remote SCSI device name may be: REMOTE:user@host: to allow remote SCSI bus scan-
ning or REMOTE:user@host:1,0,0 to access the SCSI device at host connected to SCSI bus #
1,target 0 lun 0.
To access SCSI devices via alternate transport layers, you need to prepend the SCSI device
name by a transport layer indicator. The transport layer indicator may be something like
USCSI: or ATAPI:. To get a list of supported transport layers for your platform, use dev=
To make readcd portable to all UNIX platforms, the syntax dev= devicename:scsibus,tar-
get,lun is preferred as is hides OS specific knowledge about device names from the user.
A specific OS must not necessarily support a way to specify a real device file name nor a
way to specify scsibus,target,lun.
Scsibus 0 is the default SCSI bus on the machine. Watch the boot messages for more infor-
mation or look into /var/adm/messages for more information about the SCSI configuration of
your machine. If you have problems to figure out what values for scsibus,target,lun
should be used, try the -scanbus option of cdrecord.
If no options except the dev= option have been specified, readcd goes into interactive
mode. Select a primary function and then follow the instructions.
Print version information and exit.
Sets the SCSI target for the drive, see notes above. A typical device specifica-
tion is dev=6,0 . If a filename must be provided together with the numerical tar-
get specification, the filename is implementation specific. The correct filename
in this case can be found in the system specific manuals of the target operating
system. On a FreeBSD system without CAM support, you need to use the control
device (e.g. /dev/rcd0.ctl). A correct device specification in this case may be
On Linux, drives connected to a parallel port adapter are mapped to a virtual SCSI
bus. Different adapters are mapped to different targets on this virtual SCSI bus.
If no dev option is present, cdrecord will try to get the device from the
If the argument to the dev= option does not contain the characters ',', '/', '@' or
':', it is interpreted as an label name that may be found in the file
/etc/default/cdrecord (see FILES section).
If no dev= option is present, or if the dev= option only contains a transport spec-
ifyer but no address, readcd tries to scan the SCSI address space for CD-ROM
drives. If exactly one is found, this is used by default.
Set the default SCSI command timeout value to # seconds. The default SCSI command
timeout is the minimum timeout used for sending SCSI commands. If a SCSI command
fails due to a timeout, you may try to raise the default SCSI command timeout above
the timeout value of the failed command. If the command runs correctly with a
raised command timeout, please report the better timeout value and the correspond-
ing command to the author of the program. If no timeout option is present, a
default timeout of 40 seconds is used.
Set the misc debug value to # (with debug=#) or increment the misc debug level by
one (with -d). If you specify -dd, this equals to debug=2. This may help to find
problems while opening a driver for libscg. as well as with sector sizes and sec-
tor types. Using -debug slows down the process and may be the reason for a buffer
Tell the scg-driver to modify the kernel debug value while SCSI commands are run-
Do not print out a status report for failed SCSI commands.
-v Increment the level of general verbosity by one. This is used e.g. to display the
progress of the process.
-V Increment the verbose level with respect of SCSI command transport by one. This
helps to debug problems during the process, that occur in the CD-Recorder. If you
get incomprehensible error messages you should use this flag to get more detailed
output. -VV will show data buffer content in addition. Using -V or -VV slows down
f=file Specify the filename where the output should be written or the input should be
taken from. Using '-' as filename will cause readcd to use stdout resp. stdin.
-w Switch to write mode. If this option is not present, readcd reads from the speci-
Scans the whole CD or the range specified by the sectors=range for C2 errors. C2
errors are errors that are uncorrectable after the second stage of the 24/28 +
28/32 Reed Solomon correction system at audio level (2352 bytes sector size). If an
audio CD has C2 errors, interpolation is needed to hide the errors. If a data CD
has C2 errors, these errors are in most cases corrected by the ECC/EDC code that
makes 2352 bytes out of 2048 data bytes. The ECC/EDC code should be able to correct
about 100 C2 error bytes per sector.
If you find C2 errors you may want to reduce the speed using the speed= option as
C2 errors may be a result of dynamic unbalance on the medium.
Scans the whole CD or the range specified by the sectors=range for C1/C2/CU errors.
In non-verbose mode, only a summary is printed. With -v, a line for each non error
free second is printed. with -vv, a line for each second is printed. This scan
method only works for a few drives.
In this mode, readcd reads CD data sectors in uncorrected audio mode and then tries
to correct the data using the ECC/EDC decoder library from Heiko EiBfeldt. As this
library implements looping over two layers of error correction, readcd may be able
to correct more data than the firmware of the CD-ROM drive.
This option is currently experimental and only applicable with CD media and cur-
rently only supports plain 2048 Byte CD-ROM sectors.
Scans the whole DVD or the range specified by the sectors=range for pisum8 errors.
In non-verbose mode, only a summary is printed. With -v, a line for each non error
free block of 8 * 32 kB is printed. with -vv, a line for each block of 8 * 32 kB
is printed. This scan method only works for a few drives.
Scans the whole DVD or the range specified by the sectors=range for pif errors. In
non-verbose mode, only a summary is printed. With -v, a line for each non error
free block of 32 kB is printed. with -vv, a line for each block of 32 kB is
printed. This scan method only works for a few drives.
-plot This option modified the behavior for -cxscan, -pi8scan and -pifscan. The output
is better suited for gnuplot.
Scan all SCSI devices on all SCSI busses and print the inquiry strings. This option
may be used to find SCSI address of the devices on a system. The numbers printed
out as labels are computed by: bus * 100 + target
Specify a sector range that should be read. The range is specified by the starting
sector number, a minus sign and the ending sector number. The end sector is not
included in the list, so sectors=0-0 will not read anything and may be used to
check for a CD in the drive.
Set the speed factor of the read or write process to #. # is an integer, repre-
senting a multiple of the audio speed. This is about 150 KB/s for CD-ROM and about
172 KB/s for CD-Audio. If no speed option is present, readcd will use maximum
speed. Only MMC compliant drives will benefit from this option. The speed of non
MMC drives is not changed.
Using a lower speed may increase the readability of a CD or DVD.
ts=# Set the maximum transfer size for a single SCSI command to #. The syntax for the
ts= option is the same as for cdrecord fs=# or sdd bs=#.
If no ts= option has been specified, readcd defaults to a transfer size of 256 kB.
If libscg gets lower values from the operating system, the value is reduced to the
maximum value that is possible with the current operating system. Sometimes, it
may help to further reduce the transfer size or to enhance it, but note that it may
take a long time to find a better value by experimenting with the ts= option.
Do not truncate the output file when opening it.
Retrieve a full TOC from the current disk and print it in hex.
-clone Do a clone read. Read the CD with all sub-channel data and a full TOC. The full
TOC data will be put into a file with similar name as with the f= option but the
suffix .toc added.
Do not abort if the high level error checking in readcd found an uncorrectable
error in the data stream.
Switch the drive into a mode where it ignores read errors in data sectors that are
a result of uncorrectable ECC/EDC errors before reading. If readcd completes, the
error recovery mode of the drive is switched back to the remembered old mode.
Set the retry count for high level retries in readcd to #. The default is to do
128 retries which may be too much if you like to read a CD with many unreadable
Meter the SCSI command overhead time. This is done by executing several commands
1000 times and printing the total time used. If you divide the displayed times by
1000, you get the average overhead time for a single command.
Print read-speed at # locations. The purpose of this option is to create a list of
read speed values suitable for e.g. gnuplot. The speed values are calculated
assuming that 1000 bytes are one kilobyte as documented in the SCSI standard. The
output data created for this purpose is written to stdout.
Output the speed values for meshpoints=# as factor based on single speed of the
current medium. This only works if readcd is able to determine the current medium
For all examples below, it will be assumed that the drive is connected to the primary SCSI
bus of the machine. The SCSI target id is set to 2.
To read the complete media from a CD-ROM writing the data to the file cdimage.raw:
readcd dev=2,0 f=cdimage.raw
To read sectors from range 150 ... 10000 from a CD-ROM writing the data to the file cdim-
readcd dev=2,0 sectors=150-10000 f=cdimage.raw
To write the data from the file cdimage.raw (e.g. a filesystem image from mkisofs) to a
readcd dev=2,0 -w f=cdimage.raw
RSH If the RSH environment is present, the remote connection will not be created via
rcmd(3) but by calling the program pointed to by RSH. Use e.g. RSH=/usr/bin/ssh
to create a secure shell connection.
Note that this forces cdrecord to create a pipe to the rsh(1) program and disallows
cdrecord to directly access the network socket to the remote server. This makes it
impossible to set up performance parameters and slows down the connection compared
to a root initiated rcmd(3) connection.
RSCSI If the RSCSI environment is present, the remote SCSI server will not be the program
/opt/schily/sbin/rscsi but the program pointed to by RSCSI. Note that the remote
SCSI server program name will be ignored if you log in using an account that has
been created with a remote SCSI server program as login shell.
cdrecord(1), mkisofs(1), scg(7), fbk(7), rcmd(3), ssh(1).
If you don't want to allow users to become root on your system, readcd may safely be
installed suid root. This allows all users or a group of users with no root privileges to
use readcd. Readcd in this case will only allow access to CD-ROM type drives- To give all
user access to use readcd, enter:
chown root /usr/local/bin/readcd
chmod 4711 /usr/local/bin/readcd
To give a restricted group of users access to readcd enter:
chown root /usr/local/bin/readcd
chgrp cdburners /usr/local/bin/readcd
chmod 4710 /usr/local/bin/readcd
and add a group cdburners on your system.
Never give write permissions for non root users to the /dev/scg? devices unless you would
allow anybody to read/write/format all your disks.
You should not connect old drives that do not support disconnect/reconnect to either the
SCSI bus that is connected to the CD-Recorder or the source disk.
When using readcd with the broken Linux SCSI generic driver. You should note that readcd
uses a hack, that tries to emulate the functionality of the scg driver. Unfortunately,
the sg driver on Linux has several severe bugs:
o It cannot see if a SCSI command could not be sent at all.
o It cannot get the SCSI status byte. Readcd for that reason cannot report failing
SCSI commands in some situations.
o It cannot get real DMA count of transfer. Readcd cannot tell you if there is an
DMA residual count.
o It cannot get number of bytes valid in auto sense data. Readcd cannot tell you if
device transfers no sense data at all.
o It fetches to few data in auto request sense (CCS/SCSI-2/SCSI-3 needs >= 18).
A typical error message for a SCSI command looks like:
readcd: I/O error. test unit ready: scsi sendcmd: no error
CDB: 00 20 00 00 00 00
status: 0x2 (CHECK CONDITION)
Sense Bytes: 70 00 05 00 00 00 00 0A 00 00 00 00 25 00 00 00 00 00
Sense Key: 0x5 Illegal Request, Segment 0
Sense Code: 0x25 Qual 0x00 (logical unit not supported) Fru 0x0
Sense flags: Blk 0 (not valid)
cmd finished after 0.002s timeout 40s
The first line gives information about the transport of the command. The text after the
first colon gives the error text for the system call from the view of the kernel. It usu-
ally is: I/O error unless other problems happen. The next words contain a short descrip-
tion for the SCSI command that fails. The rest of the line tells you if there were any
problems for the transport of the command over the SCSI bus. fatal error means that it
was not possible to transport the command (i.e. no device present at the requested SCSI
The second line prints the SCSI command descriptor block for the failed command.
The third line gives information on the SCSI status code returned by the command, if the
transport of the command succeeds. This is error information from the SCSI device.
The fourth line is a hex dump of the auto request sense information for the command.
The fifth line is the error text for the sense key if available, followed by the segment
number that is only valid if the command was a copy command. If the error message is not
directly related to the current command, the text deferred error is appended.
The sixth line is the error text for the sense code and the sense qualifier if available.
If the type of the device is known, the sense data is decoded from tables in scsierrs.c .
The text is followed by the error value for a field replaceable unit.
The seventh line prints the block number that is related to the failed command and text
for several error flags. The block number may not be valid.
The eight line reports the timeout set up for this command and the time that the command
really needed to complete.
If you want to actively take part on the development of cdrecord, you may join the cdwrit-
ing mailing list by sending mail to:
and include the word subscribe in the body. The mail address of the list is:
Additional information can be found on:
If you have support questions, send them to:
If you have definitely found a bug, send a mail to:
To subscribe, use:
See attributes(5) for descriptions of the following attributes:
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|Availability | SUNWmkcd |
|Interface Stability | Unstable |
This utility is part of cdrtools. The source for cdrtools is available on http://openso-
Joerg Schilling Version 2.0 READCD(1)