NAME
rmt — remote magnetic-tape protocol module
DESCRIPTION
rmt
is a program used by the remote dump and restore programs
for manipulating a magnetic tape drive
through an interprocess communication
(IPC)
connection.
The
fbackup
and
frecover
commands also use
rmt
to achieve remote backup capability (see
fbackup(1M)
and
frecover(1M)).
rmt
is normally started up with an
rexec()
or
rcmd()
call (see
rexec(3N)
and
rcmd(3N)).
rmt
accepts requests specific to the manipulation of magnetic tapes,
performs the commands, then responds with a status indication.
DDS
devices that emulate magnetic tapes are also supported.
All responses are in
ASCII
and in one of two forms.
Successful commands have responses of
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
errno(2)
and
error-message
is the corresponding error string as printed from a call to
perror()
(see
perror(3C)).
The protocol is comprised of the following commands:
- 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()
(see
open(2)).
If a device is already open,
it is closed before a new open is performed.
- odevice\nmode\n
Open the specified
device
using the indicated
mode.
device
is a full pathname and
mode
is an
ASCII
representation of an octal number suitable for passing to
open().
If a device is already open,
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()
operation using the specified parameters (see
lseek(2)).
The response value is that returned from by
lseek().
- 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 by
write()
(see
write(2)).
- Rcount\n
Read
count
bytes of data from the open device.
If
count
exceeds the size of the data buffer (10 Kbytes),
it is truncated to the data buffer size.
rmt
then performs the requested
read()
and responds with
Acount-read\n
if the read was successful.
Otherwise an error is returned in the standard format.
If the read was successful, the data read is then sent.
- Ioperation\ncount\n
Perform a
MTIOCOP
ioctl()
command using the specified parameters.
Parameters are interpreted as
ASCII
representations of the decimal values to be placed 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.
- 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).
- s
Return the status of the open device, as obtained with a
fstat()
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).
f
Return the status of the open device, as obtained with a
fstat()
call.
If the operation was successful, an
ACK
is sent with the size of the status buffer,
then the status buffer is sent in the following
ASCII
format:
machine<blank>value<newline>
stat_struct_member_name<blank>value<newline>
The end of the data is indicated by an
ASCII NULL
character.
See
/usr/include/sys/stat.h
for the
struct stat
definition.
In addition to the struct stat information,
there is an entry in the buffer describing the machine type
as returned from a
uname()
call (see
uname(2)).
In the above format ``machine'' is a key word.
All fields except
st_spare4
of the
struct stat
are returned.
- m
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 the following
ASCII
format:
machine<blank>value<newline>
mtget_struct_member_name<blank>value<newline>
The end of the data is indicated by an
ASCII NULL
character.
See
/usr/include/sys/mtio.h
for the
struct mtget
definition.
In addition to the struct mtget information there is an
entry in the buffer describing the machine type as returned from a
uname()
call.
In the above format "machine" is a keyword.
Any other command causes
rmt
to exit.
RETURN VALUE
Device status is returned in the field
mt_gstat.
/usr/include/sys/mtio.h
contains defined macros for checking the status bits.
DIAGNOSTICS
All responses are of the form described above.
WARNINGS
Use of this command for remote file access protocol is discouraged.
AUTHOR
rmt
was developed by the University of California, Berkeley.
Printable version
