rmt - Allows remote access to magnetic tape devices
The rmt command is started as a server process when requests from an rdump
or rrestore call enter the system to operate a storage device through an
interprocess communications connection. After the remote programs have fin-
ished, rmt exits and will be started again at the next request. The rmt
command is normally invoked with an rexec or rcmd system call.
This process performs the commands described in the following table and
responds with a status indication to tell a user the result of the com-
manded process. When the rmt command is called with a filename specified as
the debug-output-file parameter, all status responses are passed to the
debug-output-file in ASCII and in one of two possible formats. Conse-
quently, a system administrator can debug both software and hardware prob-
lems associated with previously issued backup commands to storage devices.
Responses to successful commands are in the format:
where A identifies a normal response, number is an integer that defines the
number of the response as an ASCII integer, and \n is a newline in the C-
Responses to unsuccessful commands are in the format:
where E identifies a response to an error, error_number is one of the pos-
sible error numbers values described in intro(2), error_message is the
corresponding error-message string, which is output in response to a call
to perror(3), and\n is a newline.
Debug information returned by rmt is stored in the named debug-output-file
file. The rmt command is called from the rdump or rrestore process with no
file argument only when the debug-output-file parameter is specified. To
activate the debug option of rmt your system administrator should rename
the original rmt to rmt.ORG, for example, and create a new shell executable
rmt that calls rmt.ORG debug-output-file.
The rdump command starts remote server /usr/sbin/rmt or /etc/rmt on
the client machine to access the storage medium. Another vendor's
rdump command may fail because rmt is not located in /etc. To avoid
this problem, it may be necessary to provide a symbolic link on the
Tru64 UNIX machine pointing to /usr/sbin/rmt as shown in the following
ln -s /usr/sbin/rmt /etc/rmt
All numerical arguments of the following commands are transferred as ASCII
O device option
Opens the device, which must be a full pathname. The option parameter
is a option value suitable for the open system call. When the device is
successfully opened, the response is A0\n.
Closes the current open device. When this command is successful, the
response is A0\n.
L offset whence
Performs a seek operation. The offset and whence parameters have the
same significance as the offset and whence parameters of the lseek sys-
tem call. When this command successfully completes, the response is
An\n, where n has the same value returned by a normally successful
lseek system call.
Writes data to the device (see the O command above). The rmt command
reads count bytes from the connection. This process is aborted when an
EOF (End-of-File) is detected before the number of characters specified
by count is transferred. The response to this command is An\n, where n
is the number of characters written.
Reads count bytes of data from the open device. When the value of
count exceeds the size of the data buffer (10 kilobytes), the number of
characters read is truncated to the data buffer size. The rmt command
then does the requested read operation. The response to this command is
An\n, where n is the number of characters read.
I operation count
Performs an ioctl system call on the open device. The operation parame-
ter is a value passed to the mt_op member of a type mtop structure for
an MTIOCTOP ioctl (magnetic tape operation) command. Valid values for
the magnetic tape operations are defined in the /usr/include/sys/mtio.h
include file. The count parameter is the value to pass to the mt_count
member of the type mtop structure and specifies the number of opera-
tions performed on the tape drive. The response to this command is
An\n, where n is the count.
S Returns the status of the open device, which is obtained with a
MTIOCGET ioctl system call. A successful response to this command is
An\n, where n is the size of the status buffer, together with the con-
tents of the status buffer in binary.
Specifies the command path
Describes the possible error numbers
A header file that defines magnetic tape operations
Commands: rdump(8), rrestore(8)
Functions: rcmd(3), rexec(3), open(2), ioctl(2)