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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
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.
Adjust the number of mounts after which the filesystem will be
checked by e2fsck(8). If max-mount-counts is 0 or -1, the num-
ber 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 filesys-
tem 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.
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
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
continue Continue normal execution.
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 alloca-
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.
Set the default hash algorithm used for filesystems
with hashed b-tree directories. Valid algorithms
accepted are: legacy, half_md4, and tea.
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
Set a flag in the filesystem superblock indicating
that it may be mounted using experimental kernel
code, such as the ext4dev filesystem.
Clear the test_fs flag, indicating the filesystem
should only be mounted using production-level
-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 jour-
nal (or is corrupted such that it appears to have an external
journal), but that external journal is not available. If the
Adjust the maximal time between two filesystem checks. No suf-
fix 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-depen-
dent) or -i (time-dependent) checking be enabled to force peri-
odic 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 filesys-
tem) stored within the filesystem. Note that you must be using
a kernel which has ext3 support in order to actually make use of
If this option is used to create a journal on a mounted filesys-
tem, 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 invisi-
ble, 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
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:
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.
journal, the Linux kernel and e2fsck(8) do not cur-
rently support shared external journals yet.
Instead of specifying a device name directly, exter-
nal-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
Only one of the size or device options can be given for a
-l List the contents of the filesystem superblock, including the
current values of the parameters that can be set via this pro-
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 warn-
ing. The volume label can be used by mount(8), fsck(8), and
/etc/fstab(5) (and possibly others) by specifying LABEL=vol-
ume_label instead of a block special device name like /dev/hda5.
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 filesys-
tem fragmentation, and to allow system daemons, such as sys-
logd(8), to continue to function correctly after non-privileged
processes are prevented from writing to the filesystem. Nor-
mally, the default percentage of reserved blocks is 5%.
Set the last-mounted directory for the filesystem.
Set or clear the indicated default mount options in the filesys-
tem. Default mount options can be overridden by mount options
specified either in /etc/fstab(5) or on the command line argu-
ments to mount(8). Older kernels may not support this feature;
in particular, kernels which predate 2.4.20 will almost cer-
tainly 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 char-
acter ('^') 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.
Enable user-specified extended attributes.
acl Enable Posix Access Control Lists.
uid16 Disables 32-bit UIDs and GIDs. This is for interop-
erability with older kernels which only store and
expect 16-bit values.
When the filesystem is mounted with journalling
enabled, all data (not just metadata) is committed
into the journal prior to being written into the
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
When the filesystem is mounted with journalling
enabled, data may be written into the main filesys-
tem 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.
The file system will be mounted with barrier opera-
tions in the journal disabled. (This option is cur-
rently only supported by the ext4 file system driver
in 2.6.35+ kernels.)
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 overwrit-
ing parts of the inode table or block group descrip-
tors. This comes at the cost of increased memory
and CPU overhead, so it is enabled only for debug-
ging purposes. (This option is currently only sup-
ported by the ext4 file system driver in 2.6.35+
The file system will be mouinted with the discard
mount option. This will cause the file system
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.
The following filesystem features can be set or cleared using
Use hashed b-trees to speed up lookups in large
Store file type information in directory entries.
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 formated file system with flex_bg
Use a journal to ensure filesystem consistency even
across unclean shutdowns. Setting the filesystem
feature is equivalent to using the -j option.
Filesystem can contain files that are greater than
2GB. (Modern kernels set this feature automatically
when a file > 2GB is created.)
Reserve space so the block group descriptor table
may grow in the future. Tune2fs only supports
clearing this filesystem feature.
Limit the number of backup superblocks to save space
on large filesystems.
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
Set the number of reserved filesystem blocks.
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 cor-
rupted 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
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
Set the universally unique identifier (UUID) of the filesystem
to UUID. The format of the UUID is a series of hex digits sepa-
rated 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.
We haven't found any bugs yet. That doesn't mean there aren't any...
tune2fs was written by Remy Card <Remy.Card@linux.org>. It is cur-
rently being maintained by Theodore Ts'o <firstname.lastname@example.org>. tune2fs