rmt



RMT(8)                    System management commands                    RMT(8)




NAME

       rmt - remote magtape protocol module


SYNOPSIS

       rmt


DESCRIPTION

       Rmt  is a program used by the remote dump(8), restore(8) or tar(1) pro-
       grams in manipulating a magnetic tape  drive  through  an  interprocess
       communication  connection.  Rmt is normally started up with an rexec(3)
       or rcmd(3) call.

       The rmt program accepts requests specific to the manipulation  of  mag-
       netic tapes, performs the commands, then responds with a status indica-
       tion.  All responses are in ASCII and  in  one  of  the  following  two
       forms.

       Successful commands have responses of:
              Anumber\n

       where number is an ASCII representation of a decimal number.

       Unsuccessful commands are responded to with:
              Eerror-number\nerror-message\n

       where  error-number  is  one of the possible error numbers described in
       intro(2) and error-message is the corresponding error string as printed
       from a call to perror(3).

       The  protocol is comprised of the following commands, which are sent as
       indicated - no spaces are supplied between the command  and  its  argu-
       ments, or between its arguments, and \n indicates that a newline should
       be supplied:

       Odevice\nmode\n
              Open the specified device using the indicated mode.  Device is a
              full  pathname  and mode is an ASCII representation of a decimal
              number suitable for passing to open(2).  If a device had already
              been opened, it is closed before a new open is performed.

       Cdevice\n
              Close  the  currently  open  device.   The  device  specified is
              ignored.

       Lwhence\noffset\n
              Perform an lseek(2) operation using  the  specified  parameters.
              The response value is that returned from the lseek call.

       Wcount\n
              Write data onto the open device.  Rmt reads count bytes from the
              connection, aborting if a premature end-of-file is  encountered.
              The response value is that returned from the write(2) call.

       Rcount\n
              Read  count bytes of data from the open device. If count exceeds
              the size of the data buffer (10 kilobytes), it is  truncated  to
              the  data  buffer size.  Rmt then performs the requested read(2)
              and responds with Acount-read\n if the read was successful; oth-
              erwise  an error in the standard format is returned. If the read
              was successful, the data read is then sent.

       Ioperation\ncount\n
              Perform a MTIOCOP ioctl(2) command using the  specified  parame-
              ters.    The   parameters   are   interpreted   as   the   ASCII
              representations of the decimal values to place in the mt_op  and
              mt_count  fields  of  the structure used in the ioctl call.  The
              return value is the count parameter when the operation  is  suc-
              cessful.

              By  issuing  the I-1\n0\n command, a client will specify that he
              is using the VERSION 1 protocol.

              For a VERSION 0 client, the operation parameter is the  platform
              mt_op value (could be different if the client and the rmt server
              are on two different platforms). For a  VERSION  1  client,  the
              operation parameter is standardized as below:

              0      Issue a MTWEOF command (write count end-of-file records).

              1      Issue a MTFSF command  (forward  space  over  count  file
                     marks).

              2      Issue  a  MTBSF  command  (backward space over count file
                     marks).

              3      Issue a MTFSR command (forward space  count  inter-record
                     gaps).

              4      Issue  a MTBSR command (backward space count inter-record
                     gaps).

              5      Issue a MTREW command (rewind).

              6      Issue  a  MTOFFL  command  (rewind  and  put  the   drive
                     offline).

              7      Issue a MTNOP command (no operation, set status only).

       ioperation\ncount\n
              Perform an extended MTIOCOP ioctl(2) command using the specified
              parameters. The parameters are interpreted as the  ASCII  repre-
              sentations  of  the  decimal  values  to  place in the mt_op and
              mt_count fields of the structure used in the  ioctl  call.   The
              return  value  is the count parameter when the operation is suc-
              cessful. The possible operations are:

              0      Issue a MTCACHE command (switch cache on).

              1      Issue a MTNOCACHE command (switch cache off).

              2      Issue a MTRETEN command (retension the tape).

              3      Issue a MTERASE command (erase the entire tape).

              4      Issue a MTEOM command (position to end of media).

              5      Issue a MTNBSF command (backward  space  count  files  to
                     BOF).

       S      Return  the  status  of the open device, as obtained with a MTI-
              OCGET ioctl call.  If the operation was successful, an “ack”  is
              sent  with the size of the status buffer, then the status buffer
              is sent (in binary,  which  is  non-portable  between  different
              platforms).

       ssub-command
              This  is  a  replacement  for  the  previous S command, portable
              across different platforms. If the open  device  is  a  magnetic
              tape,  return  members of the magnetic tape status structure, as
              obtained with a MTIOCGET ioctl call. If the open device is not a
              magnetic  tape,  an error is returned. If the MTIOCGET operation
              was successful, the numerical value of the structure  member  is
              returned in decimal. The following sub commands are supported:

              T      return  the content of the structure member mt_type which
                     contains the type of the magnetic tape device.

              D      return the content of the structure member mt_dsreg which
                     contains the "drive status register".

              E      return the content of the structure member mt_erreg which
                     contains the "error register". This structure member must
                     be  retrieved first because it is cleared after each MTI-
                     OCGET ioctl call.

              R      return the content of the structure member mt_resid which
                     contains the residual count of the last I/O.

              F      return  the  content  of  the  structure member mt_fileno
                     which contains the file number of the current tape  posi-
                     tion.

              B      return the content of the structure member mt_blkno which
                     contains the block number of the current tape position.

              f      return the content of the structure member mt_flags which
                     contains MTF_ flags from the driver.

              b      return  the  content  of the structure member mt_bf which
                     contains the optimum blocking factor.

       Any other command causes rmt to exit.


DIAGNOSTICS

       All responses are of the form described above.


SEE ALSO

       rcmd(3), rexec(3), /usr/include/sys/mtio.h, rdump(8), rrestore(8)


BUGS

       People should be discouraged from using this for a remote  file  access
       protocol.


AUTHOR

       The dump/restore backup suit was ported to Linux’s Second Extended File
       System by Remy Card <card@Linux.EU.Org>. He maintained the initial ver-
       sions of dump (up and including 0.4b4, released in january 1997).

       Starting    with   0.4b5,   the   new   maintainer   is   Stelian   Pop
       <stelian@popies.net>.


AVAILABILITY

       The dump/restore backup suit  is  available  from  <http://dump.source-
       forge.net>


HISTORY

       The rmt command appeared in 4.2BSD.



BSD                      version 0.4b40 of May 2, 2005                  RMT(8)

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