rmt(8)rmt(8)NAMErmt - Allows remote access to magnetic tape devices
SYNOPSISrmt [debug-output-file]
DESCRIPTION
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 com‐
manded process. When the rmt command is called with a filename speci‐
fied 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. 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:
Anumber\n
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:
Eerror_number error_message\n
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 administra‐
tor should rename the original rmt to rmt.ORG, for example, and create
a new shell executable rmt that calls rmt.ORG debug-output-file.
Note
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 exam‐
ple: 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 MTIOC‐
TOP ioctl (magnetic tape operation) command. Valid values for the mag‐
netic 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. 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.
FILES
Specifies the command path Describes the possible error numbers A
header file that defines magnetic tape operations
SEE ALSO
Commands: rdump(8), rrestore(8)
Functions: rcmd(3), rexec(3), open(2), ioctl(2)rmt(8)