dumpfs(8) System Manager's Manual dumpfs(8)Name
dumpfs - dump file system information
The command prints out the super block and cylinder group information for the file system or special device specified. The listing is very
long and detailed. This command is useful mostly for finding out certain file system information such as the file system block size and
minimum free space percentage.
See Alsodisktab(5), fs(5), fsck(8), newfs(8), tunefs(8)dumpfs(8)
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TUNEFS(8) BSD System Manager's Manual TUNEFS(8)NAME
tunefs -- tune up an existing UFS file system
tunefs [-A] [-a enable | disable] [-e maxbpg] [-f avgfilesize] [-j enable | disable] [-J enable | disable] [-k held-for-metadata-blocks]
[-L volname] [-l enable | disable] [-m minfree] [-N enable | disable] [-n enable | disable] [-o space | time] [-p] [-s avgfpdir]
[-S size] [-t enable | disable] special | filesystem
The tunefs utility is designed to change the dynamic parameters of a UFS file system which affect the layout policies. The tunefs utility
cannot be run on an active file system. To change an active file system, it must be downgraded to read-only or unmounted.
The parameters which are to be changed are indicated by the flags given below:
-A The file system has several backups of the super-block. Specifying this option will cause all backups to be modified as well as the
primary super-block. This is potentially dangerous - use with caution.
-a enable | disable
Turn on/off the administrative POSIX.1e ACL enable flag.
Indicate 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.
Specify the expected average file size.
-j enable | disable
Turn on/off soft updates journaling.
-J enable | disable
Turn on/off gjournal flag.
Set the amount of space to be held for metadata blocks. When set, the file system preference routines will try to save the specified
amount of space immediately following the inode blocks in each cylinder group for use by metadata blocks. Clustering the metadata
blocks speeds up random file access and decreases the running time of fsck(8). While this option can be set at any time, it is most
effective if set before any data is loaded into the file system. By default newfs(8) sets it to half of the space reserved to min-
Add/modify an optional file system volume label.
-l enable | disable
Turn on/off MAC multilabel flag.
Specify the percentage of space held back from normal users; the minimum free space threshold. The default value used is 8%. Note
that lowering the threshold can adversely affect performance:
o Settings of 5% and less force space optimization to always be used which will greatly increase the overhead for file writes.
o The file system's ability to avoid fragmentation will be reduced when the total free space, including the reserve, drops below
15%. As free space approaches zero, throughput can degrade by up to a factor of three over the performance obtained at a 10%
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 enable | disable
Turn on/off the administrative NFSv4 ACL enable flag.
-n enable | disable
Turn on/off soft updates.
-o space | time
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. Optimization for space has much higher overhead for file writes. The kernel normally changes the preference automatically
as the percent fragmentation changes on the file system.
-p Show a summary of what the current tunable settings are on the selected file system. More detailed information can be obtained from
the dumpfs(8) utility.
Specify the expected number of files per directory.
Specify the softdep journal size in bytes. The minimum is 4M.
-t enable | disable
Turn on/off the TRIM enable flag. If enabled, and if the underlying device supports the BIO_DELETE command, the file system will
send a delete request to the underlying device for each freed block. The trim enable flag is typically set when the underlying
device uses flash-memory as the device can use the delete command to pre-zero or at least avoid copying blocks that have been
At least one of the above flags is required.
/etc/fstab read this to determine the device file for a specified mount point.
SEE ALSO fs(5), dumpfs(8), gjournal(8), growfs(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 utility appeared in 4.2BSD.
This utility does not work on active 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 cannot tune a fish.
BSD June 22, 2011 BSD