NAME¶
tunefs —
tune up an existing file
system
SYNOPSIS¶
tunefs |
[-A]
[-a enable |
disable] [-e
maxbpg]
[-f
avgfilesize]
[-J enable |
disable] [-L
volname]
[-l enable |
disable] [-m
minfree]
[-N enable |
disable] [-n
enable | disable]
[-o space |
time]
[-p]
[-s
avgfpdir] special |
filesystem |
DESCRIPTION¶
The
tunefs utility is designed to change the dynamic
parameters of a 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.
- -e
maxbpg
- 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.
- -f
avgfilesize
- Specify the expected average file size.
- -J
enable | disable
- Turn on/off gjournal flag.
- -L
volname
- Add/modify an optional file system volume label.
- -l
enable | disable
- Turn on/off MAC multilabel flag.
- -m
minfree
- 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:
- Settings of 5% and less force space optimization to
always be used which will greatly increase the overhead for file
writes.
- 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%
threshold.
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.
- -s
avgfpdir
- Specify the expected number of files per directory.
At least one of the above flags is required.
FILES¶
- /etc/fstab
- read this to determine the device file for a specified
mount point.
SEE ALSO¶
fs(5),
dumpfs(8),
gjournal(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 utility appeared in
4.2BSD.
BUGS¶
This utility should work on active 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 cannot tune a fish.