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Commands Reference, Volume 4
rmt Command
Purpose
Allows remote access to magnetic tape devices.
Syntax
rmt
Description
The rmt command allows remote
access to magnetic tape devices. The remote dump and restore programs use
the rmt command as a remote magnetic tape protocol module.
The rmt command is normally started with a rexec or rcmd subroutine.
The rmt command accepts requests
specific to the manipulation of magnetic tapes, performs the commands, and
then responds with a status indication. All responses are in ASCII and in
one of two forms. Successful commands receive responses of Axxx, where xxx is an ASCII representation
of a decimal number. Unsuccessful commands receive responses of Eyyy error-message, where yyy is one of the
possible error numbers described in the errno.h file
and error-message is the corresponding error string
as printed from a call to the perror subroutine. The
protocol is comprised of the following subcommands.
Subcommands
ODeviceMode |
Opens the device specified by the Device
parameter using the mode indicated by the Mode parameter.
The value of the Device parameter is a full path name,
and that of the Mode parameter is an ASCII representation
of a decimal number suitable for passing to the open
subroutine. An open device is closed before a new open operation is performed. |
CDevice |
Closes the open device. The device specified with the Device parameter is ignored. |
LWhenceOffset |
Performs an lseek operation using the specified
parameters. The lseek subroutine returns the response
value. |
WCount |
Writes data onto the open device. From the connection, the rmt command reads the number of bytes specified by the Count parameter, ending if a premature end-of-file is encountered. The write subroutine returns the response value. |
RCount |
Reads, from the open device, the number of bytes of data specified
by the Count parameter. The rmt
command then performs the requested read operation and responds with Azzz, where zzz is the number of bytes read
if the operation was successful. The data read is then sent. Otherwise, an
error in the standard format is returned. |
IOperationCount |
Performs an STIOCTOP ioctl subroutine using
the specified parameters. The parameters are interpreted as the ASCII representations
of the decimal values to place in the mt op and mt count fields of the structure used in the ioctl
subroutine. The return value is the value of the Count parameter when the operation is successful. |
Any other subcommand causes the rmt command to exit.
Note: For the R and W subcommands, if the Count parameter specifies more bytes than the connection can handle,
the data will be truncated to a size that can be handled.
Exit Status
This command returns the following exit values:
0 |
Successful completion. |
>0 |
An error occurred. |
Files
/usr/sbin/rmt |
Contains the rmt command. |
/usr/include/sys/errno.h |
Describes the possible error numbers. |
Related Information
The rdump
command, rrestore command.
The rexec subroutine.
The rmt special file.
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