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TUNEFS(8)                   System Manager's Manual                  TUNEFS(8)

     tunefs - tune up an existing file system

     tunefs [-AFN] [-a enable | disable] [-e maxbpg] [-g avgfilesize]
            [-h avgfpdir] [-l logsize] [-m minfree] [-o optimize_preference]
            [-p enable | disable] [-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
             anything changed by tunefs.  -A is ignored when -N is specified.

     -a enable | disable
             Turn on/off the administrative NFSv4 ACL enable flag.

     -e maxbpg
             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
             cylinder 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 cylinder 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.

     -F      Indicates that special is a file system image, rather than a
             device name or file system mount point.  special will be accessed

     -g avgfilesize
             This specifies the expected average file size.

     -h avgfpdir
             This specifies the expected number of files per directory.

     -l logsize
             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
             logging enabled.

     -m minfree
             This value specifies the percentage of space held back from
             normal 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.

     -N      Display all the settable options (after any changes from the
             tuning options) but do not cause any of them to be changed.

     -o optimize_preference
             The file system can either try to minimize the time spent
             allocating blocks, or it can attempt to minimize the space
             fragmentation 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
             problematical, and the file system can be optimized for time.

             optimize_preference can be specified as either space or time.

     -p enable | disable
             Turn on/off the administrative POSIX.1e ACL enable flag.

     -q quota
             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.

     -S sectorsize
             changes the fsbtodb value in the superblock to reflect a
             particular 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 10.99                   January 17, 2022                   NetBSD 10.99