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  sys-
       tems  are  using  a library simulation of this driver.  Possible syntax
       is: dev= scsibus,target,lun or dev= target,lun.  In  the  latter  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  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:scsi-

       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.

       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= device-
       name:scsibus,target,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  0  is the default SCSI bus on the machine. Watch the boot mes-
       sages 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 cdrecord.


       If  no  options except the dev= option have been specified, readcd goes
       into interactive mode.  Select a primary function and then  follow  the

              Print version information and exit.

              Sets  the SCSI target for the drive, see notes above.  A typical
              device specification is dev=6,0 .  If a filename  must  be  pro-
              vided  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  sup-
              port,  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:@ .

              On Linux, drives connected to a parallel port adapter are mapped
              to a virtual SCSI bus. Different adapters are mapped to  differ-
              ent targets on this virtual SCSI bus.

              If no dev option is present, cdrecord will try to get the device
              from the CDR_DEVICE environment.

              If the argument to the dev= option does not contain the  charac-
              ters  ’,’,  ’/’,  ’@’ or ’:’, it is interpreted as an label name
              that may be found in the file /etc/cdrecord.conf (see FILES sec-

              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.

       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.

       -silent, -s
              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  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.

       f=file Specify  the  filename where the output should be written or the
              inout 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 specified device.

              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.

              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

              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.

       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 maimum 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  simi-
              lar 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 sectors.

              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.  gnu-
              plot.  The speed values are calculated assuming that 1000  bytes
              are  one kilobyte as documented in the SCSI standard.  The ouput
              data created for this purpose is written to stdout.

              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.


       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.



       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  broken  Linux  SCSI  generic  driver.   You
       should  note  that  readcd uses a hack, that tries to emulate the func-
       tionality of the scg driver.  Unfortunately, the sg driver on Linux has
       several severe bugs:

       ·      It cannot see if a SCSI command could not be sent at all.

       ·      It cannot get the SCSI status byte.  Readcd for that reason can-
              not 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  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 cdwriting mailing list by sending mail to:


       and include the word subscribe in the body.  The mail  address  of  the
       list is:



       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:

       To subscribe, use:

Joerg Schilling                   Version 2.0                        READCD(1)

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