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 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 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.
All numerical arguments of the following commands are transferred as ASCII strings: Opens the device, which must be a full pathname. The flag parameter is a flag 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) delim off