tune2fs - adjust tunable filesystem parameters on ext2/ext3/ext4 filesystems
] [ -c max-mount-counts
] [ -e
] [ -f
] [ -i
] [ -j
] [ -J
] [ -m reserved-blocks-percentage
] [ -r
] [ -s sparse-super-flag
] [ -g group
] [ -C
] [ -E extended-options
] [ -L
] [ -M last-mounted-directory
] [ -O
[,...] ] [ -Q quota-options
] [ -T
] [ -U UUID
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
program, or by using the dumpe2fs(8)
specifier can either be a filename (i.e., /dev/sda1), or a
LABEL or UUID specifier: " LABEL=volume-name
". (i.e., LABEL=home or
- -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
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
- -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
- Continue normal execution.
- Remount filesystem read-only.
- 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:
- 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'.
- 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.
- 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.
- 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
- 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 system drivers.
- Set a flag in the filesystem superblock indicating that it
may be mounted using experimental kernel code, such as the ext4dev
- Clear the test_fs flag, indicating the filesystem should
only be mounted using production-level filesystem code.
- 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. If the filesystem appears to require
journal replay, the -f flag must be specified twice to proceed.
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.
- 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.
- 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:
- 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
- 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.
- 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
- Only one of the size or device options can be
given for a filesystem.
- List the contents of the filesystem superblock, including
the current values of the parameters that can be set via this
- -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
- -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
- Enable debugging code for this filesystem.
- 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.
- Enable user-specified extended attributes.
- Enable Posix Access Control Lists.
- Disables 32-bit UIDs and GIDs. This is for interoperability
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 main filesystem.
- 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.
- 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.
- 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.)
- 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+
- 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.)
- 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+
- -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
- Use hashed b-trees to speed up lookups for large
- Allow more than 65000 subdirectories per directory.
- Enable the use of extent trees to store the location of
data blocks in inodes.
- Enable the extended inode fields used by ext4.
- 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 formatted file system
with flex_bg enabled.
- Use a journal to ensure filesystem consistency even across
unclean shutdowns. Setting the filesystem feature is equivalent to using
the -j option.
- Support files larger than 2 terabytes in size.
- Filesystem can contain files that are greater than
- Reserve space so the block group descriptor table may grow
in the future. Tune2fs only supports clearing this filesystem
- Enable or disable multiple mount protection (MMP)
- Enable internal file system quota inodes.
- Limit the number of backup superblocks to save space on
- 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
- -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:
- Sets/clears user quota inode in the superblock.
- 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
- -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
- -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 the filesystem UUID
- generate a new randomly-generated UUID
- 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
- 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...
was written by Remy Card <Remy.Card@linux.org>. It is
currently being maintained by Theodore Ts'o <email@example.com>.
uses the ext2fs library written by Theodore Ts'o
<firstname.lastname@example.org>. This manual page was written by Christian Kuhtz
<chk@data-hh.Hanse.DE>. Time-dependent checking was added by Uwe Ohse
is part of the e2fsprogs package and is available from