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NetBSD 6.1.5 - man page for tunefs (netbsd section 8)

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

NAME
     tunefs -- tune up an existing file system

SYNOPSIS
     tunefs [-AFN] [-e maxbpg] [-g avgfilesize] [-h avgfpdir] [-l logsize] [-m minfree]
	    [-o optimize_preference] [-q quota] special | filesys

DESCRIPTION
     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.

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

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

     -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 subse-
	     quently 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 exclu-
	     sively large files, this parameter should be set higher.

     -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 filesys-
	     tem is mounted.  The size of an existing in-filesystem journaling log file can not
	     be changed.

     -m minfree
	     This value specifies the percentage of space held back from normal users; the mini-
	     mum free space threshold.	The default value is set during creation of the filesys-
	     tem, 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 thresh-
	     old.

     -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 min-
	     free (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.

     -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/dis-
	     able all types at once.

	     After enabling a quota, fsck_ffs(8) has to be run to compute the correct quota val-
	     ues.

SEE ALSO
     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).

HISTORY
     The tunefs command appeared in 4.2BSD.

BUGS
     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 tuned.

     You can tune a file system, but you can't tune a fish.

BSD					December 15, 2010				      BSD
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