1 .\" Copyright (c) 1983, 1991, 1993
2 .\" The Regents of the University of California. All rights reserved.
4 .\" Redistribution and use in source and binary forms, with or without
5 .\" modification, are permitted provided that the following conditions
7 .\" 1. Redistributions of source code must retain the above copyright
8 .\" notice, this list of conditions and the following disclaimer.
9 .\" 2. Redistributions in binary form must reproduce the above copyright
10 .\" notice, this list of conditions and the following disclaimer in the
11 .\" documentation and/or other materials provided with the distribution.
12 .\" 3. Neither the name of the University nor the names of its contributors
13 .\" may be used to endorse or promote products derived from this software
14 .\" without specific prior written permission.
16 .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
17 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
20 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
28 .\" @(#)tunefs.8 8.2 (Berkeley) 12/11/93
36 .Nd tune up an existing UFS file system
40 .Op Fl a Cm enable | disable
42 .Op Fl f Ar avgfilesize
43 .Op Fl j Cm enable | disable
44 .Op Fl J Cm enable | disable
45 .Op Fl k Ar held-for-metadata-blocks
47 .Op Fl l Cm enable | disable
49 .Op Fl N Cm enable | disable
50 .Op Fl n Cm enable | disable
51 .Op Fl o Cm space | time
55 .Op Fl t Cm enable | disable
56 .Ar special | filesystem
60 utility is designed to change the dynamic parameters of a UFS file system
61 which affect the layout policies.
64 utility cannot be run on an active file system.
65 To change an active file system,
66 it must be downgraded to read-only or unmounted.
68 The parameters which are to be changed are indicated by the flags
70 .Bl -tag -width indent
72 The file system has several backups of the super-block.
74 this option will cause all backups to be modified as well as the
76 This is potentially dangerous - use with caution.
77 .It Fl a Cm enable | disable
78 Turn on/off the administrative POSIX.1e ACL enable flag.
80 Indicate the maximum number of blocks any single file can
81 allocate out of a cylinder group before it is forced to begin
82 allocating blocks from another cylinder group.
83 Typically this value is set to about one quarter of the total blocks
85 The intent is to prevent any single file from using up all the
86 blocks in a single cylinder group,
87 thus degrading access times for all files subsequently allocated
88 in that cylinder group.
89 The effect of this limit is to cause big files to do long seeks
90 more frequently than if they were allowed to allocate all the blocks
91 in a cylinder group before seeking elsewhere.
92 For file systems with exclusively large files,
93 this parameter should be set higher.
94 .It Fl f Ar avgfilesize
95 Specify the expected average file size.
96 .It Fl j Cm enable | disable
97 Turn on/off soft updates journaling.
99 Enabling journaling reduces the time spent by
101 cleaning up a filesystem after a crash to a few seconds from minutes to hours.
102 Without journaling, the time to recover after a crash is a function
103 of the number of files in the filesystem and the size of the filesystem.
104 With journaling, the time to recover after a crash is a function of the
105 amount of activity in the filesystem in the minute before the crash.
106 Journaled recovery time is usually only a few seconds and never
109 The drawback to using journaling is that the writes to its log adds
110 an extra write load to the media containing the filesystem.
111 Thus a write-intensive workload will have reduced throughput on a
112 filesystem running with journaling.
114 Like all journaling filesystems, the journal recovery will only fix
115 issues known to the journal.
116 Specifically if a media error occurs,
117 the journal will not know about it and hence will not fix it.
118 Thus when using journaling, it is still necessary to run a full fsck
119 every few months or after a filesystem panic to check for and fix
120 any errors brought on by media failure.
121 A full fsck can be done by running a background fsck on a live
122 filesystem or by running with the
124 flag on an unmounted filesystem.
127 in background on a live filesystem the filesystem performance
128 will be about half of normal during the time that the background
131 Running a full fsck on a UFS filesystem is the equivalent of
132 running a scrub on a ZFS filesystem.
134 Presently it is not possible
135 to run background fsck on filesystems enabled for journaling.
136 .It Fl J Cm enable | disable
137 Turn on/off gjournal flag.
138 .It Fl k Ar held-for-metadata-blocks
139 Set the amount of space to be held for metadata blocks.
140 When set, the file system preference routines will try to save
141 the specified amount of space immediately following the inode blocks
142 in each cylinder group for use by metadata blocks.
143 Clustering the metadata blocks speeds up random file access
144 and decreases the running time of
146 While this option can be set at any time,
147 it is most effective if set before any data is loaded into the file system.
150 sets it to half of the space reserved to minfree.
152 Add/modify an optional file system volume label.
153 Legal characters are alphanumerics, dashes, and underscores.
154 .It Fl l Cm enable | disable
155 Turn on/off MAC multilabel flag.
157 Specify the percentage of space held back
158 from normal users; the minimum free space threshold.
159 The default value used is 8%.
160 Note that lowering the threshold can adversely affect performance:
163 Settings of 5% and less force space optimization to
164 always be used which will greatly increase the overhead for file
167 The file system's ability to avoid fragmentation will be reduced
168 when the total free space, including the reserve, drops below 15%.
169 As free space approaches zero, throughput can degrade by up to a
170 factor of three over the performance obtained at a 10% threshold.
173 If the value is raised above the current usage level,
174 users will be unable to allocate files until enough files have
175 been deleted to get under the higher threshold.
176 .It Fl N Cm enable | disable
177 Turn on/off the administrative NFSv4 ACL enable flag.
178 .It Fl n Cm enable | disable
179 Turn on/off soft updates.
180 .It Fl o Cm space | time
181 The file system can either try to minimize the time spent
182 allocating blocks, or it can attempt to minimize the space
183 fragmentation on the disk.
184 Optimization for space has much
185 higher overhead for file writes.
186 The kernel normally changes the preference automatically as
187 the percent fragmentation changes on the file system.
189 Show a summary of what the current tunable settings
190 are on the selected file system.
191 More detailed information can be
196 Specify the expected number of files per directory.
198 Specify the softdep journal size in bytes.
200 .It Fl t Cm enable | disable
201 Turn on/off the TRIM enable flag.
202 If enabled, and if the underlying device supports the BIO_DELETE
203 command, the file system will send a delete request to the underlying
204 device for each freed block.
205 The trim enable flag is typically set when the underlying device
206 uses flash-memory as the device can use the delete command to
207 pre-zero or at least avoid copying blocks that have been deleted.
209 Note that this does not trim blocks that are already free.
216 At least one of these flags is required.
218 .Bl -tag -width ".Pa /etc/fstab"
220 read this to determine the device file for a
221 specified mount point.
234 .%T "A Fast File System for UNIX"
235 .%J "ACM Transactions on Computer Systems 2"
239 .%O "(reprinted in the BSD System Manager's Manual, SMM:5)"
247 This utility does not work on active file systems.
248 To change the root file system, the system must be rebooted
249 after the file system is tuned.
250 .\" Take this out and a Unix Daemon will dog your steps from now until
251 .\" the time_t's wrap around.
253 You can tune a file system, but you cannot tune a fish.