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TUNEFS(8) NetBSD System Manager's Manual TUNEFS(8)
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tunefs -- tune up an existing file system
tunefs [-AFN] [-e maxbpg] [-g avgfilesize] [-h avgfpdir] [-l logsize]
[-m minfree] [-o optimize_preference] [-q quota] [-S sectorsize]
special | filesys
tunefs is designed to change the dynamic parameters of a file system
which affect the layout policies.
The following options are supported by tunefs:
-A Cause the values to be updated in all the alternate superblocks
instead of just the standard superblock. If this option is not
used, then use of a backup superblock by fsck(8) will lose any-
thing changed by tunefs. -A is ignored when -N is specified.
-F Indicates that special is a file system image, rather than a
device name or file system mount point. special will be accessed
-N Display all the settable options (after any changes from the tun-
ing options) but do not cause any of them to be changed.
This indicates the maximum number of blocks any single file can
allocate out of a cylinder group before it is forced to begin
allocating blocks from another cylinder group. Typically this
value is set to about one quarter of the total blocks in a cylin-
der group. The intent is to prevent any single file from using
up all the blocks in a single cylinder group, thus degrading
access times for all files subsequently allocated in that cylin-
der group. The effect of this limit is to cause big files to do
long seeks more frequently than if they were allowed to allocate
all the blocks in a cylinder group before seeking elsewhere. For
file systems with exclusively large files, this parameter should
be set higher.
This specifies the expected average file size.
This specifies the expected number of files per directory.
This value specifies the size of the in-filesystem journaling log
file. The default journaling log file size is described in
wapbl(4). Specifying a size of zero will cause the in-filesystem
journaling log file to be removed the next time the filesystem is
mounted. The size of an existing in-filesystem journaling log
file can not be changed directly. You need to first set the log
file size to zero, then mount the filesystem without logging
enabled (which will remove the log without creating a new one),
unmount, set the size to the new value and finally re-mount with
This value specifies the percentage of space held back from nor-
mal users; the minimum free space threshold. The default value
is set during creation of the filesystem, see newfs(8). This
value can be set to zero, however up to a factor of three in
throughput will be lost over the performance obtained at a 5%
threshold. Note that if the value is raised above the current
usage level, users will be unable to allocate files until enough
files have been deleted to get under the higher threshold.
The file system can either try to minimize the time spent allo-
cating blocks, or it can attempt to minimize the space fragmenta-
tion on the disk. If the value of minfree (see above) is less
than 5%, then the file system should optimize for space to avoid
running out of full sized blocks. For values of minfree greater
than or equal to 5%, fragmentation is unlikely to be problemati-
cal, and the file system can be optimized for time.
optimize_preference can be specified as either space or time.
enable or disable a quota. quota can be one of user, group,
nouser or nogroup to enable or disable the specified quota type.
Multiple -q can be used to enable/disable all types at once.
After enabling a quota, fsck_ffs(8) has to be run to compute the
correct quota values.
changes the fsbtodb value in the superblock to reflect a particu-
lar physical sector size. This value is ignored by the NetBSD
kernel but needed by tools like fsck_ffs(8) to access disk blocks
correctly. The minimum value is DEV_BSIZE (512).
Changing the fsbtodb value becomes necessary when a filesystem
image is created for one sector size and then transferred to a
device with a different sector size and should be applied also to
the alternate superblocks.
wapbl(4), fs(5), dumpfs(8), fsck_ffs(8), newfs(8)
M. McKusick, W. Joy, S. Leffler, and R. Fabry, "A Fast File System for
UNIX", ACM Transactions on Computer Systems 2, 3, pp 181-197, August
1984, (reprinted in the BSD System Manager's Manual, SMM:5).
The tunefs command appeared in 4.2BSD.
This program should work on mounted and active file systems. Because the
super-block is not kept in the buffer cache, the changes will only take
effect if the program is run on unmounted file systems. To change the
root file system, the system must be rebooted after the file system is
You can tune a file system, but you can't tune a fish.
NetBSD 7.0 August 9, 2014 NetBSD 7.0