NAME

       rmt - remote magnetic tape server

SYNOPSIS

       rmt

DESCRIPTION

       Rmt  provides  remote  access to files and devices for tar(1), cpio(1), and similar backup
       utilities.  It is normally called by running rsh(1)  or  ssh(1)  to  the  remote  machine,
       optionally using a different login name if one is supplied.

       The  calling  program  communicates with rmt by sending requests on its standard input and
       reading replies from the standard output.  A request consists of a request letter followed
       by  an  argument (if required) and a newline character.  Additional data, if any, are sent
       after the newline.  On success, rmt returns

           Anumber\n

       where number is an ASCII representation of a decimal return  code.   Additional  data  are
       returned after this line.  On error, the following response is returned:

           Eerrno\nerror-message\n

       where  errno is one of the system error codes, as described in errno(3), and error-message
       is a one-line human-readable description of the error, as printed by perror(3).

       Available commands and possible responses  are  discussed  in  detail  in  the  subsequent
       section.

COMMANDS

       Odevice\nflags\n
              Opens  the  device  with  given  flags.  If a device had already been opened, it is
              closed before opening the new one.

              Arguments

              device The name of the device to open.

              flags  Flags for open(2): a decimal number, or any valid O_* constant from  fcntl.h
                     (the  initial O_ may be omitted), or a bitwise or (using |) of any number of
                     these, e.g.:
                         576
                         64|512
                         CREAT|TRUNC
                     In addition, a combined form is also allowed, i.e. a decimal  mode  followed
                     by its symbolic representation.  In this case the symbolic representation is
                     given preference.

              Reply
                     A0\n on success.

              Extensions
                     BSD version allows only decimal number as flags.

       C[device]\n
              Close the currently open device.

              Arguments
                     Any arguments are silently ignored.

              Reply
                     A0\n on success.

       Lwhence\noffset\n
              Performs an lseek(2) on the currently open device with the specified parameters.

              Arguments

                     whence Where to measure offset from. Valid values are:

                             0, SET, SEEK_SET   seek from the file beginning
                             1, CUR, SEEK_CUR   seek from the current location
                             2, END, SEEK_END   seek from the file end

              Reply
                     Aoffset\n on success. The offset is the new offset in file.

              Extensions
                     BSD version allows only 0,1,2 as whence.

       Rcount\n
              Read count bytes of data from the current device.

              Arguments

                     count  number of bytes to read.

              Reply
                     On success:

                         Ardcount\n

                     followed by rdcount bytes of data read from the device.

       Wcount\n
              Writes data onto the current device.  The command is followed  by  count  bytes  of
              input data.

              Arguments

                     count  Number of bytes to write.

              Reply
                     On  success:  Awrcount\n,  where  wrcount  is  the  number of bytes actually
                     written.

       Iopcode\ncount\n
              Perform a MTIOCOP ioctl(2) command with the specified paramedters.

              Arguments

                     opcode MTIOCOP operation code.

                     count  mt_count.

              Reply
                     On success: A0\n.

       S\n    Returns the status of the currently  open  device,  as  obtained  from  a  MTIOCGET
              ioctl(2) call.

              Arguments
                     None

              Reply
                     On success: Acount\n followed by count bytes of data.

SEE ALSO

       tar(1).

BUGS

       Using this utility as a general-purpose remote file access tool is discouraged.

BUG REPORTS

       Report bugs to <bug-tar@gnu.org>.

HISTORY

       The  rmt  command  appeared in 4.2BSD.  The GNU rmt is written from scratch, using the BSD
       specification.

COPYRIGHT

       Copyright © 2013, 2018 Free Software Foundation, Inc.
       License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
       This is free software: you are free to change and redistribute it.  There is NO  WARRANTY,
       to the extent permitted by law.