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32 .\" @(#)newfs.8 8.6 (Berkeley) 5/3/95
33 .\" $FreeBSD: src/sbin/newfs/newfs.8,v 1.26.2.15 2003/05/13 12:16:08 joerg Exp $
34 .\" $DragonFly: src/sbin/newfs/newfs.8,v 1.7 2007/05/20 19:29:21 dillon Exp $
35 .\"
36 .Dd May 13, 2003
37 .Dt NEWFS 8
38 .Os
39 .Sh NAME
40 .Nm newfs ,
41 .Nm mount_mfs
42 .Nd construct a new file system
43 .Sh SYNOPSIS
44 .Nm
45 .Op Fl NCOU
46 .Op Fl S Ar sector-size
47 .Op Fl T Ar disktype
48 .Op Fl a Ar maxcontig
49 .Op Fl b Ar block-size
50 .Op Fl c Ar cylinders
51 .Op Fl d Ar rotdelay
52 .Op Fl e Ar maxbpg
53 .Op Fl f Ar frag-size
54 .Op Fl g Ar avgfilesize
55 .Op Fl h Ar avfpdir
56 .Op Fl i Ar bytes
57 .Op Fl k Ar skew
58 .Op Fl l Ar interleave
59 .Op Fl m Ar free space
60 .Op Fl n Ar rotational positions
61 .Op Fl o Ar optimization
62 .Op Fl p Ar sectors
63 .Op Fl r Ar revolutions
64 .Op Fl s Ar size
65 .Op Fl t Ar tracks
66 .Op Fl u Ar sectors
67 .Op Fl v
68 .Op Fl x Ar sectors
69 .Ar special
70 .Nm mount_mfs
71 .Op Fl NU
72 .Op Fl F Ar file
73 .Op Fl T Ar disktype
74 .Op Fl a Ar maxcontig
75 .Op Fl b Ar block-size
76 .Op Fl c Ar cylinders
77 .Op Fl d Ar rotdelay
78 .Op Fl e Ar maxbpg
79 .Op Fl f Ar frag-size
80 .Op Fl i Ar bytes
81 .Op Fl m Ar free space
82 .Op Fl n Ar rotational positions
83 .Op Fl o Ar options
84 .Op Fl s Ar size
85 .Op Fl v
86 .Ar special node
87 .Sh DESCRIPTION
88 .Nm Newfs
89 is used to initialize and clear filesystems before first use.
90 Before running
91 .Nm
92 or
93 .Nm mount_mfs ,
94 the disk must be labeled using
95 .Xr disklabel 8 .
96 .Nm Newfs
97 builds a file system on the specified special file.
98 (We often refer to the
99 .Dq special file
100 as the
101 .Dq disk ,
102 although the special file need not be a physical disk.
103 In fact, it need not even be special.)
104 Typically the defaults are reasonable, however
105 .Nm
106 has numerous options to allow the defaults to be selectively overridden.
107 .Pp
108 .Nm Mount_mfs
109 is used to build a file system in virtual memory and then mount it
110 on a specified node.
111 .Nm Mount_mfs
112 exits and the contents of the file system are lost
113 when the file system is unmounted.
114 If
115 .Nm mount_mfs
116 is sent a signal while running,
117 for example during system shutdown,
118 it will attempt to unmount its
119 corresponding file system.
120 The parameters to
121 .Nm mount_mfs
122 are the same as those to
123 .Nm .
124 If the
125 .Fl T
126 flag is specified (see below), the special file is unused.
127 Otherwise, it is only used to read the disk label which provides
128 a set of configuration parameters for the memory based file system.
129 The special file is typically that of the primary swap area,
130 since that is where the file system will be backed up when
131 free memory gets low and the memory supporting
132 the file system has to be paged.
133 .Pp
134 .Nm mount_mfs
135 creates the raw character device
136 .Pa /dev/mfs<PID>
137 to represent the backing store while the mount is active. This device may
138 be read but not written and allows swap-based MFS filesystems to be dumped
139 if desired.
140 .Pp
141 The following options define the general layout policies:
142 .Bl -tag -width indent
143 .It Fl T Ar disktype
144 For backward compatibility and for
145 .Nm mount_mfs .
146 .It Fl F Ar file
147 .Nm Mount_mfs
148 will use this file for the image of the filesystem. When
149 .Nm mount_mfs
150 exits, this file will be left behind.
151 .It Fl C
152 Tell
153 .Nm Mount_mfs
154 to copy the underlying filesystem into the MFS mount being created
155 over it.
156 .It Fl N
157 Cause the file system parameters to be printed out
158 without really creating the file system.
159 .It Fl O
160 Create a
161 .Bx 4.3
162 format filesystem.
163 This options is primarily used to build root filesystems
164 that can be understood by older boot ROMs.
165 .It Fl T
166 Use information for the specified disk from
167 .Pa /etc/disktab
168 instead of trying to get geometry information from the
169 storage device.
170 .It Fl U
171 Enables soft updates on the new filesystem.
172 .It Fl a Ar maxcontig
173 Specify the maximum number of contiguous blocks that will be
174 laid out before forcing a rotational delay (see the
175 .Fl d
176 option).
177 The default value is 1.
178 See
179 .Xr tunefs 8
180 for more details on how to set this option.
181 .It Fl b Ar block-size
182 The block size of the file system, in bytes. It must be a power of 2. The
183 default size is 16384 bytes, and the smallest allowable size is 4096 bytes.
184 The optimal block:fragment ratio is 8:1.
185 Other ratios are possible, but are not recommended,
186 and may produce unpredictable results.
187 .It Fl c Ar #cylinders/group
188 The number of cylinders per cylinder group in a file system. The default
189 is to compute the maximum allowed by the other parameters. This value is
190 dependent on a number of other parameters, in particular the block size
191 and the number of bytes per inode.
192 .It Fl d Ar rotdelay
193 This parameter once specified the minimum time in milliseconds required to
194 initiate another disk transfer on the same cylinder. It was used in determining
195 the rotationally optimal layout for disk blocks within a file. Modern disks
196 with read/write-behind achieve higher performance with this feature disabled, so
197 this value should be left at the default value of 0 milliseconds. See
198 .Xr tunefs 8
199 for more details on how to set this option.
200 .It Fl e Ar maxbpg
201 Indicate the maximum number of blocks any single file can
202 allocate out of a cylinder group before it is forced to begin
203 allocating blocks from another cylinder group.
204 The default is about one quarter of the total blocks in a cylinder group.
205 See
206 .Xr tunefs 8
207 for more details on how to set this option.
208 .It Fl f Ar frag-size
209 The fragment size of the file system in bytes. It must be a power of two
210 ranging in value between
211 .Ar blocksize Ns /8
212 and
213 .Ar blocksize .
214 The default is 2048 bytes.
215 .It Fl g Ar avgfilesize
216 The expected average file size for the file system.
217 .It Fl h Ar avgfpdir
218 The expected average number of files per directory on the file system.
219 .It Fl i Ar number of bytes per inode
220 Specify the density of inodes in the file system.
221 The default is to create an inode for every
222 .Pq 4 * Ar frag-size
223 bytes of data space.
224 If fewer inodes are desired, a larger number should be used;
225 to create more inodes a smaller number should be given.
226 One inode is required for each distinct file, so this value effectively
227 specifies the average file size on the file system.
228 .It Fl m Ar free space \&%
229 The percentage of space reserved from normal users; the minimum free
230 space threshold.
231 The default value used is
232 defined by
233 .Dv MINFREE
234 from
235 .In ufs/ffs/fs.h ,
236 currently 8%.
237 See
238 .Xr tunefs 8
239 for more details on how to set this option.
240 .It Fl n Ar number of distinguished rotational positions
241 .Xr UFS 5
242 has the ability to keep track of the availability of blocks at different
243 rotational positions, so that it could lay out the data to be picked up with
244 minimum rotational latency. This parameter specifies the default number of
245 rotational positions to distinguish.
246 .Pp
247 Nowadays this value should be set to 1 (which essentially disables the
248 rotational position table) because modern drives with read-ahead and
249 write-behind do better without the rotational position table.
250 .It Fl o Ar optimization\ preference
251 .Pq Ar space No or Ar time .
252 The file system can either be instructed to try to minimize the time spent
253 allocating blocks, or to try to minimize the space fragmentation on the disk.
254 If the value of minfree (see above) is less than 8%,
255 the default is to optimize for
256 .Ar space ;
257 if the value of minfree is greater than or equal to 8%,
258 the default is to optimize for
259 .Ar time .
260 See
261 .Xr tunefs 8
262 for more details on how to set this option.
263 .It Fl s Ar size
264 The size of the file system in sectors. This value defaults to the size of the
265 raw partition specified in
266 .Ar special
267 (in other words,
268 .Nm
269 will use the entire partition for the file system).
270 .It Fl v
271 Specify that the disk does not contain any partitions, and that
272 .Nm
273 should build a file system on the whole disk.
274 This option is useful for synthetic disks such as
275 .Nm vinum .
276 It may also be used to allow
277 .Nm
278 to operate on regular files.
279 When operating on a regular file,
280 .Nm
281 will synthesize a reasonable geometry for the filesystem.
282 .El
283 .Pp
284 The following options override the standard sizes for the disk geometry.
285 Their default values are taken from the disk label.
286 Changing these defaults is useful only when using
287 .Nm
288 to build a file system whose raw image will eventually be used on a
289 different type of disk than the one on which it is initially created
290 (for example on a write-once disk).
291 Note that changing any of these values from their defaults will make
292 it impossible for
293 .Xr fsck 8
294 to find the alternate superblocks if the standard superblock is lost.
295 .Bl -tag -width indent
296 .It Fl S Ar sector-size
297 The size of a sector in bytes (almost never anything but 512).
298 .It Fl k Ar sector \&0 skew , per track
299 Used to describe perturbations in the media format to compensate for
300 a slow controller.
301 Track skew is the offset of sector 0 on track N relative to sector 0
302 on track N-1 on the same cylinder.
303 This option is of historical importance only; modern controllers are always fast
304 enough to handle operations back-to-back.
305 .It Fl l Ar hardware sector interleave
306 Used to describe perturbations in the media format to compensate for
307 a slow controller.
308 Interleave is physical sector interleave on each track,
309 specified as the denominator of the ratio:
310 .Dl sectors read/sectors passed over
311 Thus an interleave of 1/1 implies contiguous layout, while 1/2 implies
312 logical sector 0 is separated by one sector from logical sector 1.
313 This option is of historical importance only; the physical sector layout of
314 modern disks is not visible from outside.
315 .It Fl p Ar spare sectors per track
316 Spare sectors (bad sector replacements) are physical sectors that occupy
317 space at the end of each track.
318 They are not counted as part of the sectors/track
319 .Pq Fl u
320 since they are not available to the file system for data allocation.
321 This option is of historical importance only. Modern disks perform their own
322 bad sector allocation.
323 .It Fl r Ar revolutions/minute
324 The speed of the disk in revolutions per minute. This value is no longer of
325 interest, since all the parameters which depend on it are usually disabled.
326 .It Fl t Ar #tracks/cylinder
327 The number of tracks/cylinder available for data allocation by the file
328 system.
329 The default is 1.
330 If zero is specified, the value from the device geometry will be used.
331 .It Fl u Ar sectors/track
332 The number of sectors per track available for data allocation by the file
333 system.
334 The default is 4096.
335 If zero is specified, the value from the device geometry will be used.
336 This does not include sectors reserved at the end of each track for bad
337 block replacement (see the
338 .Fl p
339 option).
340 .It Fl x Ar spare sectors per cylinder
341 Spare sectors (bad sector replacements) are physical sectors that occupy
342 space at the end of the last track in the cylinder.
343 They are deducted from the sectors/track
344 .Pq Fl u
345 of the last track of each cylinder since they are not available to the file
346 system for data allocation.
347 This option is of historical importance only. Modern disks perform their own
348 bad sector allocation.
349 .El
350 .Pp
351 The options to the
352 .Nm mount_mfs
353 command are as described for the
354 .Nm
355 command, except for the
356 .Fl o
357 option.
358 .Pp
359 That option is as follows:
360 .Bl -tag -width indent
361 .It Fl o
362 Options are specified with a
363 .Fl o
364 flag followed by a comma separated string of options.
365 See the
366 .Xr mount 8
367 man page for possible options and their meanings.
368 .El
369 .Sh EXAMPLES
370 .Dl newfs /dev/ad3s1a
371 .Pp
372 Creates a new
373 .Xr UFS 5
374 file system on
375 .Pa ad3s1a .
376 .Nm
377 will use a block size of 16384 bytes, a fragment size of 2048 bytes
378 and the largest possible number of cylinders per group.
379 These values tend to produce better performance for most applications
380 than the historical defaults
381 (8192 byte block size and 1024 byte fragment size).
382 This large fragment size
383 may lead to large amounts of wasted space
384 on filesystems that contain a large number of small files.
385 .Pp
386 .Dl mount_mfs -s 131072 -o nosuid,nodev,nosymfollow /dev/da0s1b /tmp
387 .Pp
388 Mount a 64 MB large memory file system on
389 .Pa /tmp ,
390 with
391 .Xr mount 8
392 options
393 .Ar nosuid ,
394 .Ar nodev ,
395 and
396 .Ar nosymfollow .
397 .Sh SEE ALSO
398 .Xr fdformat 1 ,
399 .Xr disktab 5 ,
400 .Xr fs 5 ,
401 .Xr camcontrol 8 ,
402 .Xr disklabel 8 ,
403 .Xr dumpfs 8 ,
404 .Xr fsck 8 ,
405 .Xr mount 8 ,
406 .Xr tunefs 8 ,
407 .Xr vinum 8
408 .Rs
409 .%A M. McKusick
410 .%A W. Joy
411 .%A S. Leffler
412 .%A R. Fabry
413 .%T A Fast File System for UNIX
414 .%J ACM Transactions on Computer Systems 2
415 .%V 3
416 .%P pp 181-197
417 .%D August 1984
418 .%O (reprinted in the BSD System Manager's Manual)
419 .Re
420 .Sh HISTORY
421 The
422 .Nm
423 command appeared in
424 .Bx 4.2 .