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 finished,
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 commanded process. When the rmt
command is called with a filename specified as the debugoutput-file
parameter, all status responses are passed to
the debug-output-file in ASCII and in one of two possible
formats. Consequently, a system administrator can debug
both software and hardware problems 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-language idiom.
Responses to unsuccessful commands are in the format:
where E identifies a response to an error, error_number is
one of the possible 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 debugoutput-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
example: ln -s /usr/sbin/rmt /etc/rmt
All numerical arguments of the following commands are
transferred as ASCII strings: 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. Performs a seek operation. The offset
and whence parameters have the same significance as the
offset and whence parameters of the lseek system 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.
Performs an ioctl system call on the open device. The
operation parameter 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 operations performed on the tape drive.
The response to this command is An\n, where n is the
count. 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 contents 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)
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