tune2fs - adjust tunable filesystem parameters on ext2/ext3/ext4 filesystems
] [ -c max-mount-counts
] [ -e
] [ -f
] [ -i
] [ -I new_inode_size
] [ -J journal-options
] [ -m
] [ -o
] [ -p mmp_update_interval
] [ -r
] [ -s sparse-super-flag
] [ -g group
] [ -C
] [ -E extended-options
] [ -L
] [ -M last-mounted-directory
] [ -O
[,...] ] [ -Q quota-options
] [ -T
] [ -U UUID
] [ -z
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-label
". (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 the
- 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
- 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
- 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 filesystem.
- 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
- -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.
- Change the inode size used by the file system. This requires rewriting the
inode table, so it requires that the file system is checked for
consistency first using e2fsck(8). This operation can also take a
while and the file system can be corrupted and data lost if it is
interrupted while in the middle of converting the file system.
- 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 10,240,000 filesystem blocks. There must be enough free space in
the filesystem to create a journal of that size.
- 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 tune2fs(8).
- Only one of the size or device options can be given for a
- 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
- -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
- -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
- 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+ kernels.)
- 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
- 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
- Use hashed b-trees to speed up lookups for large directories.
- Allow more than 65000 subdirectories per directory.
- Enable file system level encryption. Tune2fs currently only
supports setting this filesystem feature.
- Enable the use of extent trees to store the location of data blocks in
inodes. Tune2fs currently only supports setting this filesystem
- 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
- Support files larger than 2 terabytes in size.
- Filesystem can contain files that are greater than 2GB.
- Store a checksum to protect the contents in each metadata block.
- Enable or disable multiple mount protection (MMP) feature.
- Enable project ID tracking. This is used for project quota tracking.
- Enable internal file system quota inodes.
- Force the kernel to mount the file system read-only.
- 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.
Tune2fs currently only supports setting this filesystem
- 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. The 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
- After setting or clearing sparse_super, uninit_bg,
filetype, or resize_inode filesystem features, the file
system may require being checked using e2fsck(8) 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
- -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
- Sets/clears user quota inode in the superblock.
- Sets/clears group quota inode in the superblock.
- Sets/clears project 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 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.
- -z undo_file
- Before overwriting a file system block, write the old contents of the
block to an undo file. This undo file can be used with e2undo(8) to
restore the old contents of the file system should something go wrong. If
the empty string is passed as the undo_file argument, the undo file will
be written to a file named tune2fs- device.e2undo in the directory
specified via the E2FSPROGS_UNDO_DIR environment variable.
WARNING: The undo file cannot be used to recover from a power or system
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 <firstname.lastname@example.org>.
uses the ext2fs library written by Theodore Ts'o
<email@example.com>. 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