1.\" Copyright (c) 1983, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 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.\" 4. 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. 15.\" 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 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)tunefs.8 8.2 (Berkeley) 12/11/93 29.\" $FreeBSD$ 30.\" 31.Dd October 21, 2009 32.Dt TUNEFS 8 33.Os 34.Sh NAME 35.Nm tunefs 36.Nd tune up an existing file system 37.Sh SYNOPSIS 38.Nm 39.Op Fl A 40.Op Fl a Cm enable | disable 41.Op Fl e Ar maxbpg 42.Op Fl f Ar avgfilesize 43.Op Fl J Cm enable | disable 44.Op Fl L Ar volname 45.Op Fl l Cm enable | disable 46.Op Fl m Ar minfree 47.Op Fl N Cm enable | disable 48.Op Fl n Cm enable | disable 49.Op Fl o Cm space | time 50.Op Fl p 51.Op Fl s Ar avgfpdir 52.Ar special | filesystem 53.Sh DESCRIPTION 54The 55.Nm 56utility is designed to change the dynamic parameters of a file system 57which affect the layout policies. 58The 59.Nm 60utility cannot be run on an active file system. 61To change an active file system, 62it must be downgraded to read-only or unmounted. 63.Pp 64The parameters which are to be changed are indicated by the flags 65given below: 66.Bl -tag -width indent 67.It Fl A 68The file system has several backups of the super-block. 69Specifying 70this option will cause all backups to be modified as well as the 71primary super-block. 72This is potentially dangerous - use with caution. 73.It Fl a Cm enable | disable 74Turn on/off the administrative POSIX.1e ACL enable flag. 75.It Fl e Ar maxbpg 76Indicate the maximum number of blocks any single file can 77allocate out of a cylinder group before it is forced to begin 78allocating blocks from another cylinder group. 79Typically this value is set to about one quarter of the total blocks 80in a cylinder group. 81The intent is to prevent any single file from using up all the 82blocks in a single cylinder group, 83thus degrading access times for all files subsequently allocated 84in that cylinder group. 85The effect of this limit is to cause big files to do long seeks 86more frequently than if they were allowed to allocate all the blocks 87in a cylinder group before seeking elsewhere. 88For file systems with exclusively large files, 89this parameter should be set higher. 90.It Fl f Ar avgfilesize 91Specify the expected average file size. 92.It Fl J Cm enable | disable 93Turn on/off gjournal flag. 94.It Fl L Ar volname 95Add/modify an optional file system volume label. 96.It Fl l Cm enable | disable 97Turn on/off MAC multilabel flag. 98.It Fl m Ar minfree 99Specify the percentage of space held back 100from normal users; the minimum free space threshold. 101The default value used is 8%. 102Note that lowering the threshold can adversely affect performance: 103.Bl -bullet 104.It 105Settings of 5% and less force space optimization to 106always be used which will greatly increase the overhead for file 107writes. 108.It 109The file system's ability to avoid fragmentation will be reduced 110when the total free space, including the reserve, drops below 15%. 111As free space approaches zero, throughput can degrade by up to a 112factor of three over the performance obtained at a 10% threshold. 113.El 114.Pp 115If the value is raised above the current usage level, 116users will be unable to allocate files until enough files have 117been deleted to get under the higher threshold. 118.It Fl N Cm enable | disable 119Turn on/off the administrative NFSv4 ACL enable flag. 120.It Fl n Cm enable | disable 121Turn on/off soft updates. 122.It Fl o Cm space | time 123The file system can either try to minimize the time spent 124allocating blocks, or it can attempt to minimize the space 125fragmentation on the disk. 126Optimization for space has much 127higher overhead for file writes. 128The kernel normally changes the preference automatically as 129the percent fragmentation changes on the file system. 130.It Fl p 131Show a summary of what the current tunable settings 132are on the selected file system. 133More detailed information can be 134obtained from the 135.Xr dumpfs 8 136utility. 137.It Fl s Ar avgfpdir 138Specify the expected number of files per directory. 139.El 140.Pp 141At least one of the above flags is required. 142.Sh FILES 143.Bl -tag -width ".Pa /etc/fstab" 144.It Pa /etc/fstab 145read this to determine the device file for a 146specified mount point. 147.El 148.Sh SEE ALSO 149.Xr fs 5 , 150.Xr dumpfs 8 , 151.Xr gjournal 8 , 152.Xr newfs 8 153.Rs 154.%A M. McKusick 155.%A W. Joy 156.%A S. Leffler 157.%A R. Fabry 158.%T "A Fast File System for UNIX" 159.%J "ACM Transactions on Computer Systems 2" 160.%N 3 161.%P pp 181-197 162.%D August 1984 163.%O "(reprinted in the BSD System Manager's Manual, SMM:5)" 164.Re 165.Sh HISTORY 166The 167.Nm 168utility appeared in 169.Bx 4.2 . 170.Sh BUGS 171This utility does not work on active file systems. 172To change the root file system, the system must be rebooted 173after the file system is tuned. 174.\" Take this out and a Unix Daemon will dog your steps from now until 175.\" the time_t's wrap around. 176.Pp 177You can tune a file system, but you cannot tune a fish. 178