aboutsummaryrefslogtreecommitdiff
path: root/sbin/mdconfig/mdconfig.8
blob: b91ffb3cb916faec569eb363c93e0e2cc4bd0122 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
.\" Copyright (c) 1993 University of Utah.
.\" Copyright (c) 1980, 1989, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\" Copyright (c) 2000
.\"	Poul-Henning Kamp  All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" the Systems Programming Group of the University of Utah Computer
.\" Science Department.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"     @(#)vnconfig.8	8.1 (Berkeley) 6/5/93
.\" from: src/usr.sbin/vnconfig/vnconfig.8,v 1.19 2000/12/27 15:30:29
.\"
.\" $FreeBSD$
.\"
.Dd December 21, 2018
.Dt MDCONFIG 8
.Os
.Sh NAME
.Nm mdconfig
.Nd create and control memory disks
.Sh SYNOPSIS
.Nm
.Fl a
.Fl t Ar type
.Op Fl n
.Oo Fl o Oo Cm no Oc Ns Ar option Oc ...
.Op Fl f Ar file
.Op Fl s Ar size
.Op Fl S Ar sectorsize
.Op Fl u Ar unit
.Op Fl x Ar sectors/track
.Op Fl y Ar heads/cylinder
.Op Fl L Ar label
.Nm
.Fl d
.Fl u Ar unit
.Op Fl o Oo Cm no Oc Ns Ar force
.Nm
.Fl r
.Fl u Ar unit
.Fl s Ar size
.Op Fl o Oo Cm no Oc Ns Ar force
.Nm
.Fl l
.Op Fl n
.Op Fl v
.Op Fl f Ar file
.Op Fl u Ar unit
.Nm
.Ar file
.Sh DESCRIPTION
The
.Nm
utility creates and controls
.Xr md 4
devices.
.Pp
Options indicate an action to be performed:
.Bl -tag -width indent
.It Fl a
Attach a memory disk.
This will configure and attach a memory disk with the
parameters specified and attach it to the system.
If the
.Fl u Ar unit
option is not provided, the newly created device name will be printed on stdout.
.It Fl d
Detach a memory disk from the system and release all resources.
.It Fl r
Resize a memory disk.
.It Fl t Ar type
Select the type of the memory disk.
.Bl -tag -width "malloc"
.It Cm malloc
Storage for this type of memory disk is allocated with
.Xr malloc 9 .
This limits the size to the malloc bucket limit in the kernel.
If the
.Fl o Cm reserve
option is not set, creating and filling a large
malloc-backed memory disk is a very easy way to
panic the system.
.It Cm vnode
A file specified with
.Fl f Ar file
becomes the backing store for this memory disk.
.It Cm swap
Storage for this type of memory disk is allocated from buffer
memory.
Pages get pushed out to swap when the system is under memory
pressure, otherwise they stay in the operating memory.
Using
.Cm swap
backing is generally preferred instead of using
.Cm malloc
backing.
.It Cm null
Bitsink; all writes do nothing, all reads return zeroes.
.El
.It Fl f Ar file
Filename to use for the vnode type memory disk.
The
.Fl a
and
.Fl t Ar vnode
options are implied if not specified.
.It Fl l
List configured devices.
If given with
.Fl u ,
display details about that particular device.
If given with
.Fl f Ar file ,
display
.Xr md 4
device names of which
.Ar file
is used as the backing store.
If both of
.Fl u
and
.Fl f
options are specified,
display devices which match the two conditions.
If the
.Fl v
option is specified, show all details.
.It Fl n
When printing
.Xr md 4
device names, print only the unit number without the
.Xr md 4
prefix.
.It Fl s Ar size
Size of the memory disk.
.Ar Size
is the number of 512 byte sectors unless suffixed with a
.Cm b , k , m , g , t ,
or
.Cm p
which
denotes byte, kilobyte, megabyte, gigabyte, terabyte and petabyte respectively.
When used without the
.Fl r
option, the
.Fl a
and
.Fl t Ar swap
options are implied if not specified.
.It Fl S Ar sectorsize
Sectorsize to use for the memory disk, in bytes.
.It Fl x Ar sectors/track
See the description of the
.Fl y
option below.
.It Fl y Ar heads/cylinder
For
.Cm malloc
or
.Cm vnode
backed devices, the
.Fl x
and
.Fl y
options can be used to specify a synthetic geometry.
This is useful for constructing bootable images for later download to
other devices.
.It Fl L Ar label
Associate a label (arbitrary string) with the new memory disk.
The label can then be inspected with
.Bd -literal -offset indent
.Nm Fl l v
.Ed
.It Fl o Oo Cm no Oc Ns Ar option
Set or reset options.
.Bl -tag -width indent
.It Oo Cm no Oc Ns Cm async
For
.Cm vnode
backed devices: avoid
.Dv IO_SYNC
for increased performance but
at the risk of deadlocking the entire kernel.
.It Oo Cm no Oc Ns Cm cache
For
.Cm vnode
backed devices: enable/disable caching of data in system caches.
The default is to not cache.
.Pp
Accesses via the device are converted to accesses via the vnode.
The caching policy for the vnode is used initially.
This is normally to cache.
This caching policy is retained if the
.Cm cache
option is used.
Otherwise, caching is limited
by releasing data from caches soon after each access.
The release has the same semantics as the
.Dv POSIX_FADV_DONTNEED
feature of
.Xr posix_fadvise 2 .
The result is that with normal (non-zfs) caching,
buffers are released from the buffer cache soon after they are constructed,
but their data is kept in the page cache at lower priority.
.Pp
The
.Cm cache
option tends to waste memory by giving unwanted double caching,
but it saves time if there is memory to spare.
.It Oo Cm no Oc Ns Cm reserve
Allocate and reserve all needed storage from the start, rather than as needed.
.It Oo Cm no Oc Ns Cm cluster
Enable clustering on this disk.
.It Oo Cm no Oc Ns Cm compress
Enable/disable compression features to reduce memory usage.
.It Oo Cm no Oc Ns Cm force
Disable/enable extra sanity checks to prevent the user from doing something
that might adversely affect the system.
This can be used with the
.Fl d
flag to forcibly destroy an
.Xr md 4
disk that is still in use.
.It Oo Cm no Oc Ns Cm readonly
Enable/disable readonly mode.
.It Oo Cm no Oc Ns Cm verify
For
.Cm vnode
backed devices: enable/disable requesting verification of the
file used for backing store.
The type of verification depends on which security features are available.
One example of verification is testing file integrity with
checksums or cryptographic signatures.
.El
.It Fl u Ar unit
Request a specific unit number or device name for the
.Xr md 4
device instead of automatic allocation.
If a device name is specified, it must be start with
.Dq md
followed by the unit number.
.El
.Pp
The last form,
.Nm
.Ar file ,
is provided for convenience as an abbreviation of
.Nm
.Fl a
.Fl t Ar vnode
.Fl f Ar file .
.Sh EXAMPLES
Create a disk with
.Pa /tmp/boot.flp
as backing storage.
The name of the allocated unit will be printed on stdout, such as
.Dq Li md0 :
.Bd -literal -offset indent
mdconfig /tmp/boot.flp
.Ed
.Pp
Create a 1 gigabyte swap backed memory disk named
.Dq Li md3 :
.Bd -literal -offset indent
mdconfig -s 1g -u md3
.Ed
.Pp
Detach and free all resources used by
.Pa /dev/md3 :
.Bd -literal -offset indent
mdconfig -du md3
.Ed
.Pp
Show detailed information on current memory disks:
.Bd -literal -offset indent
mdconfig -lv
.Ed
.Pp
Resize the
.Dq Li md3
memory disk to 2 gigabytes:
.Bd -literal -offset indent
mdconfig -rs 2g -u md3
.Ed
.Pp
Create a 1 gigabyte swap backed disk, initialize an
.Xr ffs 7
file system on it, and mount it on
.Pa /tmp :
.Bd -literal -offset indent
mdconfig -s 1g -u md10
newfs -U /dev/md10
mount /dev/md10 /tmp
chmod 1777 /tmp
.Ed
.Pp
Create a memory disk out of an ISO 9660 CD image file,
using the first available
.Xr md 4
device, and then mount it:
.Bd -literal -offset indent
mount -t cd9660 /dev/`mdconfig -f cdimage.iso` /mnt
.Ed
.Pp
Create a file-backed device from a hard disk image that begins
with 512K of raw header information.
.Xr gnop 8
is used to skip over the header information, positioning
.Pa md1.nop
to the start of the filesystem in the image.
.Bd -literal -offset indent
mdconfig -u md1 -f diskimage.img
gnop create -o 512K md1
mount /dev/md1.nop /mnt
.Ed
.Sh SEE ALSO
.Xr open 2 ,
.Xr md 4 ,
.Xr ffs 7 ,
.Xr gpart 8 ,
.Xr mdmfs 8 ,
.Xr malloc 9
.Sh HISTORY
The
.Nm
utility first appeared in
.Fx 5.0
as a cleaner replacement for the
.Xr vn 4
and
.Xr vnconfig 8
combo.
.Sh AUTHORS
The
.Nm
utility was written by
.An Poul-Henning Kamp Aq Mt phk@FreeBSD.org .