|READCD(1)||Schily´s USER COMMANDS||READCD(1)|
readcd - read or write data Compact Discs or related madia
readcd [ dev=device ][ options ]
Readcd is used to read or write Compact Discs.
Most users do not need to care about device naming at all. If no dev= option was specified, readcd implements auto target support and automagically finds the drive in case that exactly one CD-ROM type drive is available in the system. In case that more than one CD-ROM type drive exists on the system, a list of possible device name parameters may be retrieved with readcd -scanbus or from the target example from the output of readcd dev=help, then the dev= parameter may be set based on the device listing.
The device parameter to the dev= option explained below refers to the SCSI CAM standard notation for scsibus/target/lun of the CD/DVD/BluRay-Recorder. If a file /etc/default/cdrecord exists, the parameter to the dev= option may also be a drive name label in said file (see FILES section).
If no options except the dev= option have been specified, readcd goes into interactive mode. Select a primary function and then follow the instructions.
- 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.
Note that reading in clone mode results in having no error correction at sub-channel level. Even in the main data channel, there is less error correction than with other read modes. This results in a slightly quality degradation. Avoid copying audio CDs in clone mode for this reason.
- 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 Eissfeldt. 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 currently only supports plain 2048 Byte CD-ROM sectors.
- 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.
- 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 type.
- Retrieve a full TOC from the current disk and print it in hex.
- 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.
- 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.
- Do not abort if the high level error checking in readcd found an uncorrectable error in the data stream.
- Do not truncate the output file when opening it.
- 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.
- 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.
- This option modified the behavior for -cxscan, -pi8scan and -pifscan. The output is better suited for gnuplot.
- 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 sectors.
- 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,
representing 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.
- Switch to write mode. Writing is only possible to DVD-RAM media. For other
media, use cdrecord instead. Note that cdrecord also
supports to write DVD-RAM media.
If this option is not present, readcd reads from the specified device.
- Set the SCSI target for the CD/DVD/BluRay-Recorder, see notes above. A
typical target device specification is dev=1,6,0 . If a
filename must be provided together with the numerical target
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
General SCSI addressing
The target device to the dev= option refers to the SCSI CAM standard notation for scsibus/target/lun of the CD/DVD/BluRay-Recorder. 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 latter case, the CD/DVD/BluRay-Recorder 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 implementations 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.
Remote SCSI addressing
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 scanning or REMOTE:user@host:1,0,0 to access the SCSI device at host connected to SCSI bus # 1,target 0, lun 0. In order to allow remote access to a specific host, the rscsi(1) program needs to be present and configured on the host.
Alternate SCSI transports
Cdrecord is completely based on SCSI commands but this is no problem as all CD/DVD/BluRay writers ever made use SCSI commands for the communication. Even ATAPI drives are just SCSI drives that inherently use the ATA packet interface as SCSI command transport layer build into the IDE (ATA) transport. You may need to specify an alternate transport layer on the command line if your OS does not implement a fully integrated kernel driver subsystem that allows to access any drive using SCSI commands via a single unique user interface.
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= HELP:
To make readcd portable to all UNIX platforms, the syntax dev= devicename:scsibus,target,lun is preferred as it hides OS specific knowledge about device names from the user. A specific OS may 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 information 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 readcd described below.
Using logical names for devices
If no dev option is present, readcd will try to get the device from the CDR_DEVICE environment.
If a file /etc/default/cdrecord exists, and if the argument to the dev= option or the CDR_DEVICE environment does not contain the characters ',', '/', '@' or ':', it is interpreted as a device label name that was defined in the file /etc/default/cdrecord (see FILES section).
If no dev= option and no CDR_DEVICE environment is present, or if it only contains a transport specifyer but no address notation, readcd tries to scan the SCSI address space for CD-ROM drives. If exactly one is found, this is used by default.
- debug=#, -d
- 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 sector types. Using -debug slows down the process and may be the reason for a buffer underrun.
- kdebug=#, kd=#
- Tell the scg-driver to modify the kernel debug value while SCSI commands are running.
- 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
- A comma separated list of SCSI options that are handled by libscg. The implemented options may be uptated indepentendly from applications. Currently, one option: ignore-resid is supported to work around a Linux kernel bug.
- -silent, -s
- Do not print out a status report for failed SCSI commands.
- 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 corresponding command to the author of the program. If no timeout option is present, a default timeout of 40 seconds is used.
- 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.
- 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 the process.
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 cdimage.raw:
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 DVD-RAM, call:
readcd dev=2,0 -w f=cdimage.raw
- 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
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.
- 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.
The following exit codes are used:
- No error appeared.
- A specific error appeared. This may be a usage error caused by an illegal command line or another error with a problem specific error message from readcd.
- An unspecified error appeared during the process of talking to the drive. See SCSI error message for more informations. The section DIAGNOSTICS below contains an explanation on how to read SCSI error messages.
Note that older operating systems and older shells may not support the full 32 bit range of the exit code and mask the value with 0xFF. This results in shortened exit codes in the range 0..255 where -1 is mapped to 255.
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 Linux SCSI generic driver. You should note that readcd uses a layer, that tries to emulate the functionality of the scg driver on top of the drives of the local operating system. Unfortunately, the sg driver on Linux has several flaws:
- It cannot see if a SCSI command could not be sent at all.
- It cannot get the SCSI status byte. Readcd for that reason cannot report failing SCSI commands in some situations.
- It cannot get real DMA count of transfer. Readcd cannot tell you if there is an DMA residual count.
- It cannot get number of bytes valid in auto sense data. Readcd cannot tell you if device transfers no sense data at all.
- 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 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 developer mailing list via this URL:
Joerg Schilling Seestr. 110 D-13353 Berlin Germany
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:
The interfaces provided by readcd are designed for long term stability. As readcd depends on interfaces provided by the underlying operating system, the stability of the interfaces offered by readcd depends on the interface stability of the OS interfaces. Modified interfaces in the OS may enforce modified interfaces in readcd.
|Version 3.02 2017/06/06||Joerg Schilling|