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.\"     @(#)rmt.8	8.3 (Berkeley) 6/1/94
.\"
.Dd June 1, 1994
.Dt RMT 8
.Os
.Sh NAME
.Nm rmt
.Nd remote magtape protocol module
.Sh SYNOPSIS
.Nm
.Sh DESCRIPTION
.Nm
is a program used by the remote dump and restore programs
in manipulating a magnetic tape drive through an interprocess
communication connection.
.Nm
is normally started up with an
.Xr rexec 3
or
.Xr rcmd 3
call.
.Pp
The
.Nm
program accepts requests specific to the manipulation of
magnetic tapes, performs the commands, then responds with
a status indication.  All responses are in
.Tn ASCII
and in
one of two forms.
Successful commands have responses of:
.Bd -filled -offset indent
.Sm off
.Sy A Ar number No \en
.Sm on
.Ed
.Pp
.Ar Number
is an
.Tn ASCII
representation of a decimal number.
Unsuccessful commands are responded to with:
.Bd -filled -offset indent
.Sm off
.Xo Sy E Ar error-number
.No \en Ar error-message
.No \en
.Xc
.Sm on
.Ed
.Pp
.Ar Error-number
is one of the possible error
numbers described in
.Xr intro 2
and
.Ar error-message
is the corresponding error string as printed
from a call to
.Xr perror 3 .
The protocol comprises the
following commands, which are sent as indicated - no spaces are supplied
between the command and its arguments, or between its arguments, and
.Ql \en
indicates that a newline should be supplied:
.Bl -tag -width Ds
.It Sy \&O Ns Ar device Ns \en Ns Ar mode Ns \en
Open the specified
.Ar device
using the indicated
.Ar mode .
.Ar Device
is a full pathname and
.Ar mode
is an
.Tn ASCII
representation of a decimal
number suitable for passing to
.Xr open 2 .
If a device had already been opened, it is
closed before a new open is performed.
.It Sy C Ns Ar device Ns \en
Close the currently open device.  The
.Ar device
specified is ignored.
.It Sy L Ns Ar offset Ns \en Ns Ar whence Ns \en
Perform an
.Xr lseek 2
operation using the specified parameters.
The response value is that returned from the
.Xr lseek 2
call.
.Sm off
.It Sy W Ar count No \en
.Sm on
Write data onto the open device.
.Nm
reads
.Ar count
bytes from the connection, aborting if
a premature end-of-file is encountered.
The response value is that returned from
the
.Xr write 2
call.
.Sm off
.It Sy R Ar count No \en
.Sm on
Read
.Ar count
bytes of data from the open device.
If
.Ar count
exceeds the size of the data buffer (10 kilobytes), it is
truncated to the data buffer size.
.Nm
then performs the requested
.Xr read 2
and responds with
.Sm off
.Sy A Ar count-read No \en
.Sm on
if the read was
successful; otherwise an error in the
standard format is returned.  If the read
was successful, the data read is then sent.
.It Sy I Ns Ar operation Ns \en Ns Ar count Ns \en
.Sm on
Perform a
.Dv MTIOCOP
.Xr ioctl 2
command using the specified parameters.
The parameters are interpreted as the
.Tn ASCII
representations of the decimal values
to place in the
.Ar mt_op
and
.Ar mt_count
fields of the structure used in the
.Xr ioctl 2
call.  The return value is the
.Ar count
parameter when the operation is successful.
.It Sy S
Return the status of the open device, as
obtained with a
.Dv MTIOCGET
.Xr ioctl 2
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).
.El
.Pp
Any other command causes
.Nm
to exit.
.Sh DIAGNOSTICS
All responses are of the form described above.
.Sh SEE ALSO
.Xr rcmd 3 ,
.Xr rexec 3 ,
.Xr mtio 4 ,
.Xr rdump 8 ,
.Xr rrestore 8
.Sh HISTORY
The
.Nm
command appeared in
.Bx 4.2 .
.Sh BUGS
People should be discouraged from using this for a remote
file access protocol.