1RMT(8) System management commands RMT(8)
2
6 rmt - remote magtape protocol module
7
9 rmt
10
12 Rmt is a program used by the remote dump(8), restore(8) or tar(1) pro‐
13 grams in manipulating a magnetic tape drive through an interprocess
14 communication connection. Rmt is normally started up with an rexec(3)
15 or rcmd(3) call.
16 The rmt program accepts requests specific to the manipulation of mag‐
18 netic tapes, performs the commands, then responds with a status indica‐
19 tion. All responses are in ASCII and in one of the following two
20 forms.
21 Successful commands have responses of:
23 Anumber\n
24 where number is an ASCII representation of a decimal number.
26 Unsuccessful commands are responded to with:
28 Eerror-number\nerror-message\n
29 where error-number is one of the possible error numbers described in
31 intro(2) and error-message is the corresponding error string as printed
32 from a call to perror(3).
33 The protocol is comprised of the following commands, which are sent as
35 indicated - no spaces are supplied between the command and its argu‐
36 ments, or between its arguments, and \n indicates that a newline should
37 be supplied:
38 Odevice\nmode\n
40 Open the specified device using the indicated mode. Device is a
41 full pathname and mode is an ASCII representation of a decimal
42 number suitable for passing to open(2). If a device had already
43 been opened, it is closed before a new open is performed.
44 Cdevice\n
46 Close the currently open device. The device specified is
47 ignored.
48 Lwhence\noffset\n
50 Perform an lseek(2) operation using the specified parameters.
51 The response value is that returned from the lseek call.
52 Wcount\n
54 Write data onto the open device. Rmt reads count bytes from the
55 connection, aborting if a premature end-of-file is encountered.
56 The response value is that returned from the write(2) call.
57 Rcount\n
59 Read count bytes of data from the open device. If count exceeds
60 the size of the data buffer (10 kilobytes), it is truncated to
61 the data buffer size. Rmt then performs the requested read(2)
62 and responds with Acount-read\n if the read was successful; oth‐
63 erwise an error in the standard format is returned. If the read
64 was successful, the data read is then sent.
65 Ioperation\ncount\n
67 Perform a MTIOCOP ioctl(2) command using the specified parame‐
68 ters. The parameters are interpreted as the ASCII representa‐
69 tions of the decimal values to place in the mt_op and mt_count
70 fields of the structure used in the ioctl call. The return
71 value is the count parameter when the operation is successful.
72 By issuing the I-1\n0\n command, a client will specify that he
74 is using the VERSION 1 protocol.
75 For a VERSION 0 client, the operation parameter is the platform
77 mt_op value (could be different if the client and the rmt server
78 are on two different platforms). For a VERSION 1 client, the
79 operation parameter is standardized as below:
80 0 Issue a MTWEOF command (write count end-of-file records).
82 1 Issue a MTFSF command (forward space over count file
84 marks).
85 2 Issue a MTBSF command (backward space over count file
87 marks).
88 3 Issue a MTFSR command (forward space count inter-record
90 gaps).
91 4 Issue a MTBSR command (backward space count inter-record
93 gaps).
94 5 Issue a MTREW command (rewind).
96 6 Issue a MTOFFL command (rewind and put the drive off‐
98 line).
99 7 Issue a MTNOP command (no operation, set status only).
101 ioperation\ncount\n
103 Perform an extended MTIOCOP ioctl(2) command using the specified
104 parameters. The parameters are interpreted as the ASCII repre‐
105 sentations of the decimal values to place in the mt_op and
106 mt_count fields of the structure used in the ioctl call. The
107 return value is the count parameter when the operation is suc‐
108 cessful. The possible operations are:
109 0 Issue a MTCACHE command (switch cache on).
111 1 Issue a MTNOCACHE command (switch cache off).
113 2 Issue a MTRETEN command (retension the tape).
115 3 Issue a MTERASE command (erase the entire tape).
117 4 Issue a MTEOM command (position to end of media).
119 5 Issue a MTNBSF command (backward space count files to
121 BOF).
122 S Return the status of the open device, as obtained with a MTI‐
124 OCGET ioctl call. If the operation was successful, an “ack” is
125 sent with the size of the status buffer, then the status buffer
126 is sent (in binary, which is non-portable between different
127 platforms).
128 ssub-command
130 This is a replacement for the previous S command, portable
131 across different platforms. If the open device is a magnetic
132 tape, return members of the magnetic tape status structure, as
133 obtained with a MTIOCGET ioctl call. If the open device is not a
134 magnetic tape, an error is returned. If the MTIOCGET operation
135 was successful, the numerical value of the structure member is
136 returned in decimal. The following sub commands are supported:
137 T return the content of the structure member mt_type which
139 contains the type of the magnetic tape device.
140 D return the content of the structure member mt_dsreg which
142 contains the "drive status register".
143 E return the content of the structure member mt_erreg which
145 contains the "error register". This structure member must
146 be retrieved first because it is cleared after each MTI‐
147 OCGET ioctl call.
148 R return the content of the structure member mt_resid which
150 contains the residual count of the last I/O.
151 F return the content of the structure member mt_fileno
153 which contains the file number of the current tape posi‐
154 tion.
155 B return the content of the structure member mt_blkno which
157 contains the block number of the current tape position.
158 f return the content of the structure member mt_flags which
160 contains MTF_ flags from the driver.
161 b return the content of the structure member mt_bf which
163 contains the optimum blocking factor.
164 Any other command causes rmt to exit.
166
168 All responses are of the form described above.
169
171 rcmd(3), rexec(3), /usr/include/sys/mtio.h, rdump(8), rrestore(8)
172
174 People should be discouraged from using this for a remote file access
175 protocol.
176
178 The dump/restore backup suit was ported to Linux's Second Extended File
179 System by Remy Card <card@Linux.EU.Org>. He maintained the initial ver‐
180 sions of dump (up and including 0.4b4, released in january 1997).
181 Starting with 0.4b5, the new maintainer is Stelian Pop
183 <stelian@popies.net>.
184
186 The dump/restore backup suit is available from <http://dump.source‐
187 forge.net>
188
190 The rmt command appeared in 4.2BSD.
191BSD version 0.4b43 of June 11, 2010 RMT(8)