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.TH ERMT 1 "version __VERSION__ of __DATE__" BSD "System management commands"
.SH NAME
ermt \- remote magtape protocol module with transparent encryption support
.SH SYNOPSIS
.B ermt
.SH DESCRIPTION
.B Ermt
is a program used by the remote 
.BR dump (8),
.BR restore (8)
.BR cpio (1)
or
.BR tar (1)
programs in manipulating a magnetic tape drive through an interprocess
communication connection.
.B Ermt
is normally started up with an
.BR ssh (1)
.BR rexec (3)
or
.BR rcmd (3)
call.
.PP
The 
.B ermt
program accepts requests specific to the manipulation of magnetic tapes, 
performs the commands, then responds with a status indication.  All responses 
are in
.B ASCII
and in one of the following two forms.
.PP
Successful commands have responses of:
.RS
.B A\fInumber\fR\en
.RE
.PP
where
.I number
is an
.B ASCII
representation of a decimal number.
.PP
Unsuccessful commands are responded to with:
.RS
.B E\fIerror-number\fR\en\fIerror-message\fR\en
.RE
.PP
where 
.I error-number
is one of the possible error numbers described in
.BR intro (2)
and
.I error-message
is the corresponding error string as printed from a call to
.BR perror (3).
.PP
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 \en indicates that a newline should be supplied:
.TP
.B O\fIdevice\fR\en\fImode\fR\en
Open the specified 
.I device
using the indicated
.IR mode .
.I Device
is a full pathname and
.I mode
is an
.B ASCII
representation of a decimal number suitable for passing to
.BR open (2).
If a device had already been opened, it is closed before a new open is
performed.
.TP
.B C\fIdevice\fR\en
Close the currently open device.  The
.I device
specified is ignored.
.TP
.B L\fIwhence\fR\en\fIoffset\fR\en
Perform an
.BR lseek (2)
operation using the specified parameters. The response value is that returned
from the
.B lseek
call.
.TP
.B W\fIcount\fR\en
Write data onto the open device.
.B Rmt
reads
.I count
bytes from the connection, aborting if a premature end-of-file is encountered.
The response value is that returned from the
.BR write (2)
call.
.TP
.B R\fIcount\fR\en
Read
.I count
bytes of data from the open device. If
.I count
exceeds the size of the data buffer (10 kilobytes), it is truncated to the 
data buffer size.
.B Rmt
then performs the requested 
.BR read (2)
and responds with 
.B A\fIcount-read\fR\en
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.
.TP
.B I\fIoperation\fR\en\fIcount\fR\en
Perform a
.B MTIOCOP
.BR ioctl (2)
command using the specified parameters.  The parameters are interpreted as the
.B ASCII
representations of the decimal values to place in the 
.B mt_op
and
.B mt_count
fields of the structure used in the
.B ioctl
call.  The return value is the
.I count
parameter when the operation is successful.
.IP
By issuing the
.B I-1\en0\en
command, a client will specify that he is using the VERSION 1 protocol.
.IP
For a VERSION 0 client, the
.I operation
parameter is the platform 
.B mt_op
value (could be different if the client and the
.B rmt
server are on two different platforms). For a VERSION 1 client, the 
.I operation
parameter is standardized as below:
.RS
.TP
.B 0
Issue a 
.B MTWEOF
command (write
.I count
end-of-file records).
.TP
.B 1
Issue a 
.B MTFSF
command (forward space over
.I count
file marks).
.TP
.B 2
Issue a 
.B MTBSF
command (backward space over
.I count
file marks).
.TP
.B 3
Issue a 
.B MTFSR 
command (forward space
.I count
inter-record gaps).
.TP
.B 4
Issue a 
.B MTBSR
command (backward space
.I count
inter-record gaps).
.TP
.B 5
Issue a 
.B MTREW
command (rewind).
.TP
.B 6
Issue a 
.B MTOFFL
command (rewind and put the drive offline).
.TP
.B 7
Issue a
.B MTNOP
command (no operation, set status only).
.RE
.TP
.B i\fIoperation\fR\en\fIcount\fR\en
Perform an extended
.B MTIOCOP
.BR ioctl (2)
command using the specified parameters. The parameters are interpreted as the
.B ASCII
representations of the decimal values to place in the 
.B mt_op
and
.B mt_count
fields of the structure used in the
.B ioctl
call.  The return value is the
.I count
parameter when the operation is successful. The possible operations are:
.RS
.TP
.B 0
Issue a 
.B MTCACHE
command (switch cache on).
.TP
.B 1
Issue a 
.B MTNOCACHE
command (switch cache off).
.TP
.B 2
Issue a 
.B MTRETEN
command (retension the tape).
.TP
.B 3
Issue a 
.B MTERASE
command (erase the entire tape).
.TP
.B 4
Issue a 
.B MTEOM
command (position to end of media).
.TP
.B 5
Issue a 
.B MTNBSF
command (backward space count files to BOF).
.RE
.TP
.B S
Return the status of the open device, as obtained with a
.B MTIOCGET
.B ioctl
call.  If the operation was successful, an \*(lqack\*(rq is sent with the size
of the status buffer, then the status buffer is sent (in binary, which is
non-portable between different platforms).
.TP
.BI s sub-command
This is a replacement for the previous 
.B 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
.B MTIOCGET 
ioctl call. If the open device is not a magnetic tape, an error is returned. If
the 
.B MTIOCGET
operation was successful, the numerical value of the structure member is 
returned in decimal. The following sub commands are supported:
.RS
.TP
.B T
return the content of the structure member
.B mt_type
which contains the type of the magnetic tape device.
.TP
.B D
return the content of the structure member
.B mt_dsreg
which contains the "drive status register".
.TP
.B E
return the content of the structure member
.B mt_erreg
which contains the "error register". This structure member must be retrieved
first because it is cleared after each
.B MTIOCGET
ioctl call.
.TP
.B R
return the content of the structure member
.B mt_resid
which contains the residual count of the last I/O.
.TP
.B F
return the content of the structure member
.B mt_fileno
which contains the file number of the current tape position.
.TP
.B B
return the content of the structure member
.B mt_blkno
which contains the block number of the current tape position.
.TP
.B f
return the content of the structure member
.B mt_flags
which contains MTF_ flags from the driver.
.TP
.B b
return the content of the structure member
.B mt_bf
which contains the optimum blocking factor.
.RE
.PP
Any other command causes 
.B rmt
to exit.
.SH ENCRYPTION
This version "rmt" utility - \fBe\fRrmt have a transparent encryption support.
Data is encrypted before it is written to tape, and decrypted when read.
.DQ .DQ .DQ .DQ .DQ .DQ .DQ Tools that use rmt for remote tape access (such as dump, restore, cpio
and tar) can manipulate encrypted data without modification.
.PP
.B ermt
reads the secret key from ".ermt.key" and use 
.BR openssl (1)
for perform encryption and decryption.
The symmetric cipher is currently hardwired as Blowfish.
.SH EXAMPLES
.SS Run-time setup:
- Create a user for remote tape access, which we will call "dump":
.TP
	useradd -m dump
.TP
- Generate a random key in ~dump/.ermt.key:
.PP
.EX
	su - dump
	openssl rand -out .ermt.key 32
	chmod 400 .ermt.key
.EE
.PP
Due to the way "openssl enc -kfile .ermt.key" reads the key file,
you should ensure that the key contains no \e0 or \er or \en characters,
which would prematurely truncate the key length.
.PP
- Protect the key: copy to many floppies, "od -x .ermt.key|lpr", etc.
.PP
- Set up ssh access from root (or whoever you run dump as)
.PP
- Copy the ermt binary to ~dump and change dump's shell to ~dump/ermt
.PP
.RS 
or
.RE
.PP
- If user who run backup program is a same with the user who must to run rmt, just install ermt binary into a bin folder.
.SS Backup usage:
Just dump remotely to localhost:
.PP
.EX
	dump -0u -f dump@localhost:/dev/st0 /
	restore -i -f dump@localhost:/dev/st0
	# You can use GNU tar too
.EE
.PP
If your device is doing hardware compression, it's best to turn
it off, since encrypted data compresses very poorly.
.SS Emergency decrypting:
If you need to restore a tape and
don't have access to a host running ermt,
you have two choices:
.PP
- If you have a copy of the ermt binary, run it with the -d switch
  to decrypt stdin to stdout:
.PP
.EX
	dd if=/dev/st0 bs=10k |
	(cd ~dump; ./ermt -d) |		# assuming ermt is in ~dump
	restore -i -f -
.EE
.PP
- If not, use the OpenSSL "openssl" command, which does the same thing:
.PP
.EX
	dd if=/dev/st0 bs=10k |
	openssl enc -d -kfile ~dump/.ermt.key -blowfish -nosalt -nopad |
	restore -i -f -
.EE
.PP
.SH ERRORS
If "~/.ermt.key" will not be found, any opertion will fail.
.SH DIAGNOSTICS
All responses are of the form described above.
.SH SEE ALSO
.BR ssh (1),
.BR rcmd (3),
.BR rexec (3),
.I /usr/include/sys/mtio.h,
.BR dump (8),
.BR restore (8)
.SH BUGS
People should be discouraged from using this for a remote file access protocol.
.SH AUTHOR
The
.B dump/restore
backup suit was ported to Linux's Second Extended File System by Remy Card
<card@Linux.EU.Org>. He maintained the initial versions of 
.B dump
(up and including 0.4b4, released in january 1997).
.PP
Starting with 0.4b5, the new maintainer is Stelian Pop <stelian@popies.net>.
.SH AVAILABILITY
The
.B dump/restore
backup suit is available from <http://dump.sourceforge.net>
.SH HISTORY
The
.B rmt
command appeared in 4.2BSD.

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