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na_rmt - remote magtape protocol module
/etc/rmt
/etc/rmt is a special command that can be used by remote
computers to manipulate a magnetic tape drive over a network
connection; for example, the UNIX dump and restore
commands often can either use /etc/rmt to access a remote
tape, or have rdump and rrestore variants that can do so.
/etc/rmt is normally run by the rshd daemon (see
na_rshd(8)) as a result of a remote machine making a
request to rshd to do so.
The /etc/rmt command accepts requests specific to the
manipulation of magnetic tapes, performs the commands,
then responds with a status indication. This protocol is
provided by rmt commands on many UNIX systems, although
UNIX systems may support more commands and may give more
different error codes.
All responses are in ASCII and in one of two forms. Successful
commands have responses of:
Anumber\n
number is an ASCII representation of a decimal number.
Unsuccessful commands are responded to with:
Eerror-number\nerror-message\n
error-number is one of:
2 (ENOENT)
The tape device specified in an open
request did not have a valid syntax.
6 (ENXIO)
The tape device specified in an open
request does not exist.
5 (EIO)
An I/O error occurred when performing the
request.
25 (ENOTTY)
An invalid tape operation was specified
in a ``perform special tape operation''
request.
error-message is a (UNIX-style) error string for the error
specified by error-number.
The protocol is comprised of the following commands, which
are sent as indicated - no spaces are supplied between the
command and its arguments, or between its arguments, and
\n indicates that a newline should be supplied:
Odevice\nmode\n
Open the specified device using the
indicated mode. device is a tape name of
the form described in na_tape(4) and mode is
an ASCII representation of a decimal number
specifying how the tape is to be opened:
-
0
- read-only
-
1
- write-only
-
2
- read-write
If a device had already been opened, it is
closed before a new open is performed.
Cdevice\n
Close the currently open device. The device
specified is ignored.
Lwhence\noffset\n
Performs no operation, and returns the value
of offset; UNIX-style lseek operations are
ignored on NetApp filer tape devices, just
as they are on tape devices on many UNIX
systems.
Wcount\n
Write data onto the open device. If count
exceeds the maximum data buffer size (64
kilobytes), it is truncated to that size.
/etc/rmt then reads count bytes from the
connection, aborting if a premature end-offile
is encountered. The response value is
the number of bytes written if the write
succeeds, or -1 if the write fails.
Rcount\n
Read count bytes of data from the open
device. If count exceeds the maximum data
buffer size (64 kilobytes), it is truncated
to that size. /etc/rmt then attempts to
read count bytes from the tape and responds
with Acount-read\n if the read was successful;
otherwise an error in the standard format
is returned. If the read was successful,
the data read is then sent.
Ioperation\ncount\n
Perform a special tape operation on the open
device using the specified parameters. The
parameters are interpreted as ASCII representations
of the decimal values. operation
is one of:
-
0
- write end-of-file marker
-
1
- forward space count files
-
2
- backward space count files
-
3
- forward space count tape blocks
-
4
- backward space count tape blocks
-
5
- rewind the tape
-
6
- rewind and unload the tape
The return value is the count parameter when
the operation is successful.
Any other command causes /etc/rmt to close the connection.
All responses are of the form described above.
na_tape(4), na_rshd(8)
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