READOM(1) Schily´s USER COMMANDS READOM(1)
readom – read or write data Compact Discs
readom dev=device [ options ]
Readom is used to read or write Compact Discs.
The device refers to a device location similar to the one used in the
wodim command. Refer to its manpage for details.
Also note that this version of readom uses a modified libusal library
which has a different behaviour compared to the one distributed by its
If no options except the dev= option have been specified, readom 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
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, readom 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/wodim.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.
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 libusal. 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.
Tell the usal-driver to modify the kernel debug value while SCSI
commands are running.
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
input should be taken from. Using ‘-‘ as filename will cause
readom to use stdout resp. stdin.
-w Switch to write mode. If this option is not present, readom
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, readom 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 wodim fs=# or
If no ts= option has been specified, readom defaults to a trans‐
fer size of 256 kB. If libusal gets lower values from the oper‐
ating 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 simi‐
lar name as with the f= option but the suffix .toc added.
Do not abort if the high level error checking in readom 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 readom 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 readom 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 output
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 readom 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
readom 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:
readom dev=2,0 sectors=150-10000 f=cdimage.raw
To write the data from the file cdimage.raw (e.g. a filesystem image
from genisoimage) to a DVD-RAM, call:
readom 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 wodim to create a pipe to the rsh pro‐
gram and disallows wodim to directly access the network socket
to the remote server. This makes it impossible to set up per‐
formance 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.
Unless you want to risk getting problems, readom should be run as root.
If you don’t want to allow users to become root on your system, readom
may safely be installed suid root. For more information see the addi‐
tional notes of your system/program distribution or README.suidroot
which is part of the Cdrkit source.
Documentation of the wodim program contains more technical details
which could also apply to readom.
A typical error message for a SCSI command looks like:
readom: 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 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.
The readom program described here is the Cdrkit spinoff from the origi‐
nal readcd application (see AUTHOR section for details). It may contain
bugs not present in the original implementation.
It is definitely less portable than the original implementation.
For platform specific bugs, see the corresponding README.platform file
in the Cdrkit documentation (eg. README.linux).
If you want to actively take part on the development of readom, you may
join the developer mailing list via this URL:
The mail address of the list is: email@example.com
This is application is a spinoff from the original implementation of
readcd delivered in the cdrtools package  created by Joerg
Schilling, who deserves the most credits for its success. However, he
is not involved into the development of this spinoff and therefore he
shall not be made responsible for any problem caused by it. Do not try
to get support from the original author!
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 this list or to
writing at least a short description into the Subject and “Package:
cdrkit” into the first line of the mail body.
 Cdrtools 2.01.01a08 from May 2006, http://cdrecord.berlios.de
Joerg Schilling Version 2.0 READOM(1)