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TUNE2FS(8) TUNE2FS(8)
NAME
tune2fs - adjust tunable filesystem parameters on ext2/ext3 filesystems
SYNOPSIS
tune2fs [ -l ] [ -c max-mount-counts ] [ -e errors-behavior ] [ -f ] [ -i interval-
between-checks ] [ -j ] [ -J journal-options ] [ -m reserved-blocks-percentage ] [ -o
[^]mount-options[,...] ] [ -r reserved-blocks-count ] [ -s sparse-super-flag ] [ -u user
] [ -g group ] [ -C mount-count ] [ -E extended-options ] [ -L volume-name ] [ -M last-
mounted-directory ] [ -O [^]feature[,...] ] [ -T time-last-checked ] [ -U UUID ] device
DESCRIPTION
tune2fs allows the system administrator to adjust various tunable filesystem parameters on
Linux ext2/ext3 filesystems.
OPTIONS
-c max-mount-counts
Adjust the number of mounts after which the filesystem will be checked by
e2fsck(8). If max-mount-counts is 0 or -1, the number of times the filesystem is
mounted will be disregarded by e2fsck(8) and the kernel.
Staggering the mount-counts at which filesystems are forcibly checked will avoid
all filesystems being checked at one time when using journaled filesystems.
You should strongly consider the consequences of disabling mount-count-dependent
checking entirely. Bad disk drives, cables, memory, and kernel bugs could all cor-
rupt a filesystem without marking the filesystem dirty or in error. If you are
using journaling on your filesystem, your filesystem will never be marked dirty, so
it will not normally be checked. A filesystem error detected by the kernel will
still force an fsck on the next reboot, but it may already be too late to prevent
data loss at that point.
See also the -i option for time-dependent checking.
-C mount-count
Set the number of times the filesystem has been mounted. If set to a greater value
than the max-mount-counts parameter set by the -c option, e2fsck(8) will check the
filesystem at the next reboot.
-e error-behavior
Change the behavior of the kernel code when errors are detected. In all cases, a
filesystem error will cause e2fsck(8) to check the filesystem on the next boot.
error-behavior can be one of the following:
continue Continue normal execution.
remount-ro Remount filesystem read-only.
panic Cause a kernel panic.
-E extended-options
Set extended options for the filesystem. Extended options are comma separated, and
may take an argument using the equals ('=') sign. The following extended options
are supported:
stride=stride-size
Configure the filesystem for a RAID array with stride-size filesystem
blocks. This is the number of blocks read or written to disk before
moving to next disk. This mostly affects placement of filesystem meta-
data like bitmaps at mke2fs(2) time to avoid placing them on a single
disk, which can hurt the performance. It may also be used by block
allocator.
stripe_width=stripe-width
Configure the filesystem for a RAID array with stripe-width filesystem
blocks per stripe. This is typically be stride-size * N, where N is the
number of data disks in the RAID (e.g. RAID 5 N+1, RAID 6 N+2). This
allows the block allocator to prevent read-modify-write of the parity
in a RAID stripe if possible when the data is written.
hash_alg=hash-alg
Set the default hash algorithm used for filesystems with hashed b-tree
directories. Valid algorithms accepted are: legacy, half_md4, and tea.
test_fs
Set a flag in the filesystem superblock indicating that it may be
mounted using experimental kernel code, such as the ext4dev filesystem.
^test_fs
Clear the test_fs flag, indicating the filesystem should only be
mounted using production-level filesystem code.
-f Force the tune2fs operation to complete even in the face of errors. This option is
useful when removing the has_journal filesystem feature from a filesystem which has
an external journal (or is corrupted such that it appears to have an external jour-
nal), but that external journal is not available.
WARNING: Removing an external journal from a filesystem which was not cleanly
unmounted without first replaying the external journal can result in severe data
loss and filesystem corruption.
-g group
Set the group which can use the reserved filesystem blocks. The group parameter
can be a numerical gid or a group name. If a group name is given, it is converted
to a numerical gid before it is stored in the superblock.
-i interval-between-checks[d|m|w]
Adjust the maximal time between two filesystem checks. No postfix or d result in
days, m in months, and w in weeks. A value of zero will disable the time-dependent
checking.
It is strongly recommended that either -c (mount-count-dependent) or -i (time-
dependent) checking be enabled to force periodic full e2fsck(8) checking of the
filesystem. Failure to do so may lead to filesystem corruption (due to bad disks,
cables, memory, or kernel bugs) going unnoticed, ultimately resulting in data loss
or corruption.
-j Add an ext3 journal to the filesystem. If the -J option is not specified, the
default journal parameters will be used to create an appropriately sized journal
(given the size of the filesystem) stored within the filesystem. Note that you
must be using a kernel which has ext3 support in order to actually make use of the
journal.
If this option is used to create a journal on a mounted filesystem, an immutable
file, .journal, will be created in the top-level directory of the filesystem, as it
is the only safe way to create the journal inode while the filesystem is mounted.
While the ext3 journal is visible, it is not safe to delete it, or modify it while
the filesystem is mounted; for this reason the file is marked immutable. While
checking unmounted filesystems, e2fsck(8) will automatically move .journal files to
the invisible, reserved journal inode. For all filesystems except for the root
filesystem, this should happen automatically and naturally during the next reboot
cycle. Since the root filesystem is mounted read-only, e2fsck(8) must be run from
a rescue floppy in order to effect this transition.
On some distributions, such as Debian, if an initial ramdisk is used, the initrd
scripts will automatically convert an ext2 root filesystem to ext3 if the
/etc/fstab file specifies the ext3 filesystem for the root filesystem in order to
avoid requiring the use of a rescue floppy to add an ext3 journal to the root
filesystem.
-J journal-options
Override the default ext3 journal parameters. Journal options are comma separated,
and may take an argument using the equals ('=') sign. The following journal
options are supported:
size=journal-size
Create a journal stored in the filesystem of size journal-size
megabytes. The size of the journal must be at least 1024 filesystem
blocks (i.e., 1MB if using 1k blocks, 4MB if using 4k blocks, etc.)
and may be no more than 102,400 filesystem blocks. There must be
enough free space in the filesystem to create a journal of that size.
device=external-journal
Attach the filesystem to the journal block device located on external-
journal. The external journal must have been already created using the
command
mke2fs -O journal_dev external-journal
Note that external-journal must be formatted with the same block size
as filesystems which will be using it. In addition, while there is
support for attaching multiple filesystems to a single external jour-
nal, the Linux kernel and e2fsck(8) do not currently support shared
external journals yet.
Instead of specifying a device name directly, external-journal can also
be specified by either LABEL=label or UUID=UUID to locate the external
journal by either the volume label or UUID stored in the ext2
superblock at the start of the journal. Use dumpe2fs(8) to display a
journal device's volume label and UUID. See also the -L option of
tune2fs(8).
Only one of the size or device options can be given for a filesystem.
-l List the contents of the filesystem superblock.
-L volume-label
Set the volume label of the filesystem. Ext2 filesystem labels can be at most 16
characters long; if volume-label is longer than 16 characters, tune2fs will trun-
cate it and print a warning. The volume label can be used by mount(8), fsck(8),
and /etc/fstab(5) (and possibly others) by specifying LABEL=volume_label instead of
a block special device name like /dev/hda5.
-m reserved-blocks-percentage
Set the percentage of the filesystem which may only be allocated by privileged pro-
cesses. Reserving some number of filesystem blocks for use by privileged pro-
cesses is done to avoid filesystem fragmentation, and to allow system daemons, such
as syslogd(8), to continue to function correctly after non-privileged processes are
prevented from writing to the filesystem. Normally, the default percentage of
reserved blocks is 5%.
-M last-mounted-directory
Set the last-mounted directory for the filesystem.
-o [^]mount-option[,...]
Set or clear the indicated default mount options in the filesystem. Default mount
options can be overridden by mount options specified either in /etc/fstab(5) or on
the command line arguments to mount(8). Older kernels may not support this fea-
ture; in particular, kernels which predate 2.4.20 will almost certainly ignore the
default mount options field in the superblock.
More than one mount option can be cleared or set by separating features with com-
mas. Mount options prefixed with a caret character ('^') will be cleared in the
filesystem's superblock; mount options without a prefix character or prefixed with
a plus character ('+') will be added to the filesystem.
The following mount options can be set or cleared using tune2fs:
debug Enable debugging code for this filesystem.
bsdgroups
Emulate BSD behaviour when creating new files: they will take the
group-id of the directory in which they were created. The standard
System V behaviour is the default, where newly created files take on
the fsgid of the current process, unless the directory has the setgid
bit set, in which case it takes the gid from the parent directory, and
also gets the setgid bit set if it is a directory itself.
user_xattr
Enable user-specified extended attributes.
acl Enable Posix Access Control Lists.
uid16 Disables 32-bit UIDs and GIDs. This is for interoperability with older
kernels which only store and expect 16-bit values.
journal_data
When the filesystem is mounted with journalling enabled, all data (not
just metadata) is committed into the journal prior to being written
into the main filesystem.
journal_data_ordered
When the filesystem is mounted with journalling enabled, all data is
forced directly out to the main file system prior to its metadata being
committed to the journal.
journal_data_writeback
When the filesystem is mounted with journalling enabled, data may be
written into the main filesystem after its metadata has been committed
to the journal. This may increase throughput, however, it may allow
old data to appear in files after a crash and journal recovery.
-O [^]feature[,...]
Set or clear the indicated filesystem features (options) in the filesystem. More
than one filesystem feature can be cleared or set by separating features with com-
mas. Filesystem features prefixed with a caret character ('^') will be cleared in
the filesystem's superblock; filesystem features without a prefix character or pre-
fixed with a plus character ('+') will be added to the filesystem.
The following filesystem features can be set or cleared using tune2fs:
large_file
Filesystem can contain files that are greater than 2GB. (Modern ker-
nels set this feature automatically when a file > 2GB is created.)
dir_index
Use hashed b-trees to speed up lookups in large directories.
filetype
Store file type information in directory entries.
has_journal
Use a journal to ensure filesystem consistency even across unclean
shutdowns. Setting the filesystem feature is equivalent to using the
-j option.
sparse_super
Limit the number of backup superblocks to save space on large filesys-
tems.
resize_inode
Reserve space so the block group descriptor table may grow in the
future. Tune2fs only supports clearing this filesystem feature.
uninit_bg
Allow the kernel to initialize bitmaps and inode tables and keep a high
watermark for the unused inodes in a filesystem, to reduce e2fsck(8)
time. This first e2fsck run after enabling this feature will take the
full time, but subsequent e2fsck runs will take only a fraction of the
original time, depending on how full the file system is.
After setting or clearing sparse_super, uninit_bg, filetype, or resize_inode
filesystem features, e2fsck(8) must be run on the filesystem to return the filesys-
tem to a consistent state. Tune2fs will print a message requesting that the system
administrator run e2fsck(8) if necessary. After setting the dir_index feature,
e2fsck -D can be run to convert existing directories to the hashed B-tree format.
Enabling certain filesystem features may prevent the filesystem from being mounted
by kernels which do not support those features. In particular the uninit_bg and
flex_bg features are only supported by the ext4 filesystem.
-r reserved-blocks-count
Set the number of reserved filesystem blocks.
-T time-last-checked
Set the time the filesystem was last checked using e2fsck. The time is interpreted
using the current (local) timezone. This can be useful in scripts which use a Log-
ical Volume Manager to make a consistent snapshot of a filesystem, and then check
the filesystem during off hours to make sure it hasn't been corrupted due to hard-
ware problems, etc. If the filesystem was clean, then this option can be used to
set the last checked time on the original filesystem. The format of time-last-
checked is the international date format, with an optional time specifier, i.e.
YYYYMMDD[HH[MM[SS]]]. The keyword now is also accepted, in which case the last
checked time will be set to the current time.
-u user
Set the user who can use the reserved filesystem blocks. user can be a numerical
uid or a user name. If a user name is given, it is converted to a numerical uid
before it is stored in the superblock.
-U UUID
Set the universally unique identifier (UUID) of the filesystem to UUID. The format
of the UUID is a series of hex digits separated by hyphens, like this:
"c1b9d5a2-f162-11cf-9ece-0020afc76f16". The UUID parameter may also be one of the
following:
clear clear the filesystem UUID
random generate a new randomly-generated UUID
time generate a new time-based UUID
The UUID may be used by mount(8), fsck(8), and /etc/fstab(5) (and possibly others)
by specifying UUID=uuid instead of a block special device name like /dev/hda1.
See uuidgen(8) for more information. If the system does not have a good random
number generator such as /dev/random or /dev/urandom, tune2fs will automatically
use a time-based UUID instead of a randomly-generated UUID.
BUGS
We haven't found any bugs yet. That doesn't mean there aren't any...
AUTHOR
tune2fs was written by Remy Card <Remy.Card AT linux.org>. It is currently being maintained
by Theodore Ts'o <tytso AT alum.edu>. tune2fs uses the ext2fs library written by
Theodore Ts'o <tytso AT mit.edu>. This manual page was written by Christian Kuhtz <chk@data-
hh.Hanse.DE>. Time-dependent checking was added by Uwe Ohse <uwe AT tirka.de>.
AVAILABILITY
tune2fs is part of the e2fsprogs package and is available from http://e2fsprogs.source-
forge.net.
SEE ALSO
debugfs(8), dumpe2fs(8), e2fsck(8), mke2fs(8)
E2fsprogs version 1.41.3 October 2008 TUNE2FS(8)
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On Apache
Under GNU General Public License
2012-05-26 04:16 @38.107.179.237 Crawled by CCBot/1.0 (+http://www.commoncrawl.org/bot.html)