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Updated: Wednesday, February 9, 2022

readcd (1)


readcd - read or write data Compact Discs or related madia


readcd [ dev=device ][ options ]


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.

   Device naming
       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 parame-
       ters 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 scsi-
       bus/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

   Informative options
       -help  display version information for readcd on standard output.

              Print version information and exit.

       -v     Increment  the  level of general verbosity by one.  This is used
              e.g. to display the progress of the process.

   Readcd functional options
       -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 simi-
              lar name as with the f= option but the suffix .toc added.

              Note that reading in clone mode results in having no error  cor-
              rection  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 sec-

       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.

              Output the speed values for meshpoints=# as factor based on sin-
              gle  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.  gnu-
              plot.  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.

       -plot  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 speci-
              fied  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.

       -w     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

   SCSI options
              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  spe-
              cific manuals of the target operating system.  On a FreeBSD sys-
              tem without CAM support, you need  to  use  the  control  device
              (e.g.   /dev/rcd0.ctl).   A correct device specification in this
              case may be dev=/dev/rcd0.ctl:@ .

            General SCSI addressing
              The target device to the  dev=  option  refers  to  scsibus/tar-
              get/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= device-
              name: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 com-
              mands 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:

            Portability Background
              To  make  readcd portable to all UNIX platforms, the syntax dev=
              devicename:scsibus,target,lun is preferred as it hides  OS  spe-
              cific 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,tar-
              get,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).

            Autotarget Mode
              If  no  dev= option and no CDR_DEVICE environment is present, or
              if it only contains a transport specifyer but no  address  nota-
              tion,  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  rea-
              son 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 com-
              puted by: bus * 100 + target

       -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 time-
              out, 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  bet-
              ter 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.

       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 trans-
              fer size of 256 kB. If libscg gets lower values from the operat-
              ing  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.

       -V     Increment  the verbose level with respect of SCSI command trans-
              port 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

           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

       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

              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.

       See attributes(7) for descriptions of the following attributes:

       |Availability   | media/cdrtools   |
       |Stability      | Uncommitted      |

       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

       You should not connect old drives that do not support disconnect/recon-
       nect 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:

       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 can-
              not 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).

              Source code  for  open  source  software  components  in  Oracle
              Solaris  can  be found at https://www.oracle.com/downloads/open-

              This   software   was   built   from   source    available    at
              https://github.com/oracle/solaris-userland.  The original commu-
              nity    source    was    downloaded    from      https://source-

              Further information about this software can be found on the open
              source community website at http://cdrecord.org/.

       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 usually is: I/O error unless other
       problems happen. The next words contain a  short  description  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 address).

       The second line prints the SCSI command descriptor block for the failed

       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,  fol-
       lowed  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  cur-
       rent command, the text deferred error is appended.

       The sixth line is the error text for the sense code and the sense qual-
       ifier 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

       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

       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:

       or joerg.schilling@fokus.fraunhofer.de

       To subscribe, use:

       or http://lists.berlios.de/mailman/listinfo/cdrecord-support

       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.

Joerg Schilling                   Version 3.0                        READCD(1)