rmt - Unix, Linux Command
NAME
rmt - remote magtape protocol module
SYNOPSIS
rmt DESCRIPTION
Rmt is a program used by the remote
dump(8),
restore(8)
or
tar(1)
programs in manipulating a magnetic tape drive through an interprocess
communication connection.
Rmt is normally started up with an
rexec(3)
or
rcmd(3)
call.
The
rmt program accepts requests specific to the manipulation of magnetic tapes,
performs the commands, then responds with a status indication. All responses
are in
ASCII and in one of the following two forms.
Successful commands have responses of:
Anumber\n
where
number is an
ASCII representation of a decimal number.
Unsuccessful commands are responded to with:
Eerror-number\nerror-message\n
where
error-number is one of the possible error numbers described in
intro(2)
and
error-message is the corresponding error string as printed from a call to
perror(3).
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:
Tag | Description |
Odevice\nmode\n | |
Open the specified
device using the indicated
mode. Device is a full pathname and
mode is an
ASCII representation of a decimal number suitable for passing to
open(2).
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 | |
Perform an
lseek(2)
operation using the specified parameters. The response value is that returned
from the
lseek call.
|
Wcount\n |
Write data onto the open device.
Rmt reads
count bytes from the connection, aborting if a premature end-of-file is encountered.
The response value is that returned from the
write(2)
call.
|
Rcount\n |
Read
count bytes of data from the open device. If
count exceeds the size of the data buffer (10 kilobytes), it is truncated to the
data buffer size.
Rmt then performs the requested
read(2)
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
MTIOCOP ioctl(2)
command 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 call. The return value is the
count parameter when the operation is successful.
|
|
By issuing the
I-1\n0\n command, a client will specify that he is using the VERSION 1 protocol.
|
|
For a VERSION 0 client, the
operation parameter is the platform
mt_op value (could be different if the client and the
rmt server are on two different platforms). For a VERSION 1 client, the
operation parameter is standardized as below:
Tag | Description |
0 |
Issue a
MTWEOF command (write
count end-of-file records).
|
1 |
Issue a
MTFSF command (forward space over
count file marks).
|
2 |
Issue a
MTBSF command (backward space over
count file marks).
|
3 |
Issue a
MTFSR command (forward space
count inter-record gaps).
|
4 |
Issue a
MTBSR command (backward space
count inter-record gaps).
|
5 |
Issue a
MTREW command (rewind).
|
6 |
Issue a
MTOFFL command (rewind and put the drive offline).
|
7 |
Issue a
MTNOP command (no operation, set status only).
|
|
ioperation\ncount\n | |
Perform an extended
MTIOCOP ioctl(2)
command 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 call. The return value is the
count parameter when the operation is successful. The possible operations are:
Tag | Description |
0 |
Issue a
MTCACHE command (switch cache on).
|
1 |
Issue a
MTNOCACHE command (switch cache off).
|
2 |
Issue a
MTRETEN command (retension the tape).
|
3 |
Issue a
MTERASE command (erase the entire tape).
|
4 |
Issue a
MTEOM command (position to end of media).
|
5 |
Issue a
MTNBSF command (backward space count files to BOF).
|
|
S |
Return the status of the open device, as obtained with a
MTIOCGET ioctl call. If the operation was successful, an ack is sent with the size
of the status buffer, then the status buffer is sent (in binary, which is
non-portable between different platforms).
|
ssub-command | |
This is a replacement for the previous
S command, portable across different platforms. If the open device is a magnetic
tape, return members of the magnetic tape status structure, as obtained with a
MTIOCGET ioctl call. If the open device is not a magnetic tape, an error is returned. If
the
MTIOCGET operation was successful, the numerical value of the structure member is
returned in decimal. The following sub commands are supported:
Tag | Description |
T |
return the content of the structure member
mt_type which contains the type of the magnetic tape device.
|
D |
return the content of the structure member
mt_dsreg which contains the "drive status register".
|
E |
return the content of the structure member
mt_erreg which contains the "error register". This structure member must be retrieved
first because it is cleared after each
MTIOCGET ioctl call.
|
R |
return the content of the structure member
mt_resid which contains the residual count of the last I/O.
|
F |
return the content of the structure member
mt_fileno which contains the file number of the current tape position.
|
B |
return the content of the structure member
mt_blkno which contains the block number of the current tape position.
|
f |
return the content of the structure member
mt_flags which contains MTF_ flags from the driver.
|
b |
return the content of the structure member
mt_bf which contains the optimum blocking factor.
|
|
Any other command causes
rmt to exit.
DIAGNOSTICS
All responses are of the form described above.
SEE ALSO
rdump(8),
rrestore(8)
BUGS
People should be discouraged from using this for a remote file access protocol.
AUTHOR
The
dump/restore backup suit was ported to Linuxs Second Extended File System by Remy Card
<card@Linux.EU.Org>. He maintained the initial versions of
dump (up and including 0.4b4, released in january 1997).
Starting with 0.4b5, the new maintainer is Stelian Pop <stelian@popies.net>.
AVAILABILITY
The
dump/restore backup suit is available from <http://dump.sourceforge.net>
HISTORY
The
rmt command appeared in 4.2BSD.
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