Provided by: e2fsprogs_1.42.9-3ubuntu1.3_amd64 
NAME
tune2fs - adjust tunable filesystem parameters on ext2/ext3/ext4 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[,...] ] [ -Q quota-options ] [ -T time-last-checked ]
[ -U UUID ] device
DESCRIPTION
tune2fs allows the system administrator to adjust various tunable filesystem parameters on
Linux ext2, ext3, or ext4 filesystems. The current values of these options can be
displayed by using the -l option to tune2fs(8) program, or by using the dumpe2fs(8)
program.
The device specifier can either be a filename (i.e., /dev/sda1), or a LABEL or UUID
specifier: "LABEL=volume-name" or "UUID=uuid". (i.e., LABEL=home or
UUID=e40486c6-84d5-4f2f-b99c-032281799c9d).
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
corrupt 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:
clear_mmp
Reset the MMP block (if any) back to the clean state. Use only if
absolutely certain the device is not currently mounted or being fscked,
or major filesystem corruption can result. Needs '-f'.
mmp_update_interval=interval
Adjust the initial MMP update interval to interval seconds. Specifying
an interval of 0 means to use the default interval. The specified
interval must be less than 300 seconds. Requires that the mmp feature
be enabled.
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
metadata 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.
mount_opts=mount_option_string
Set a set of default mount options which will be used when the file
system is mounted. Unlike the bitmask-based default mount options
which can be specified with the -o option, mount_option_string is an
arbitrary string with a maximum length of 63 bytes, which is stored in
the superblock.
The ext4 file system driver will first apply the bitmask-based default
options, and then parse the mount_option_string, before parsing the
mount options passed from the mount(8) program.
This superblock setting is only honored in 2.6.35+ kernels; and not at
all by the ext2 and ext3 file system drivers.
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
journal), 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 suffix or d will
interpret the number interval-between-checks as days, m as months, and w as 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.
location=journal-location
Specify the location of the journal. The argument journal-location can
either be specified as a block number, or if the number has a units
suffix (e.g., 'M', 'G', etc.) interpret it as the offset from the
beginning of the file system.
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
journal, 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, including the current values of the
parameters that can be set via this program.
-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
truncate 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
processes. Reserving some number of filesystem blocks for use by privileged
processes 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
feature; 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
commas. 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 behavior when creating new files: they will take the group-
id of the directory in which they were created. The standard System V
behavior 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.
nobarrier
The file system will be mounted with barrier operations in the journal
disabled. (This option is currently only supported by the ext4 file
system driver in 2.6.35+ kernels.)
block_validity
The file system will be mounted with the block_validity option enabled,
which causes extra checks to be performed after reading or writing from
the file system. This prevents corrupted metadata blocks from causing
file system damage by overwriting parts of the inode table or block
group descriptors. This comes at the cost of increased memory and CPU
overhead, so it is enabled only for debugging purposes. (This option
is currently only supported by the ext4 file system driver in 2.6.35+
kernels.)
discard
The file system will be mounted with the discard mount option. This
will cause the file system driver to attempt to use the trim/discard
feature of some storage devices (such as SSD's and thin-provisioned
drives available in some enterprise storage arrays) to inform the
storage device that blocks belonging to deleted files can be reused for
other purposes. (This option is currently only supported by the ext4
file system driver in 2.6.35+ kernels.)
nodelalloc
The file system will be mounted with the nodelalloc mount option. This
will disable the delayed allocation feature. (This option is currently
only supported by the ext4 file system driver in 2.6.35+ kernels.)
-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
commas. Filesystem features prefixed with a caret character ('^') will be cleared
in the filesystem's superblock; filesystem features without a prefix character or
prefixed with a plus character ('+') will be added to the filesystem. For a
detailed description of the file system features, please see the man page ext4(5).
The following filesystem features can be set or cleared using tune2fs:
dir_index
Use hashed b-trees to speed up lookups for large directories.
dir_nlink
Allow more than 65000 subdirectories per directory.
extent Enable the use of extent trees to store the location of data blocks in
inodes.
extra_isize
Enable the extended inode fields used by ext4.
filetype
Store file type information in directory entries.
flex_bg
Allow bitmaps and inode tables for a block group to be placed anywhere
on the storage media. Tune2fs will not reorganize the location of the
inode tables and allocation bitmaps, as mke2fs(8) will do when it
creates a freshly formatted file system with flex_bg enabled.
has_journal
Use a journal to ensure filesystem consistency even across unclean
shutdowns. Setting the filesystem feature is equivalent to using the
-j option.
huge_file
Support files larger than 2 terabytes in size.
large_file
Filesystem can contain files that are greater than 2GB.
resize_inode
Reserve space so the block group descriptor table may grow in the
future. Tune2fs only supports clearing this filesystem feature.
mmp Enable or disable multiple mount protection (MMP) feature.
quota Enable internal file system quota inodes.
sparse_super
Limit the number of backup superblocks to save space on large
filesystems.
uninit_bg
Allow the kernel to initialize bitmaps and inode tables lazily, and to
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
filesystem 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.
-p mmp_check_interval
Set the desired MMP check interval in seconds. It is 5 seconds by default.
-r reserved-blocks-count
Set the number of reserved filesystem blocks.
-Q quota-options
Sets 'quota' feature on the superblock and works on the quota files for the given
quota type. Quota options could be one or more of the following:
[^]usrquota
Sets/clears user quota inode in the superblock.
[^]grpquota
Sets/clears group quota inode in the superblock.
-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
Logical 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
hardware 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@linux.org>. It is currently being maintained
by Theodore Ts'o <tytso@alum.mit.edu>. tune2fs uses the ext2fs library written by
Theodore Ts'o <tytso@mit.edu>. This manual page was written by Christian Kuhtz <chk@data-
hh.Hanse.DE>. Time-dependent checking was added by Uwe Ohse <uwe@tirka.gun.de>.
AVAILABILITY
tune2fs is part of the e2fsprogs package and is available from
http://e2fsprogs.sourceforge.net.
SEE ALSO
debugfs(8), dumpe2fs(8), e2fsck(8), mke2fs(8), ext4(5)