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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | BUGS | AUTHOR | AVAILABILITY | SEE ALSO | COLOPHON |
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TUNE2FS(8) System Manager's Manual TUNE2FS(8)
tune2fs - adjust tunable file system parameters on ext2/ext3/ext4
file systems
tune2fs [ -l ] [ -c max-mount-counts ] [ -e errors-behavior ] [ -f
] [ -i interval-between-checks ] [ -I new_inode_size ] [ -j ] [ -J
journal-options ] [ -m reserved-blocks-percentage ] [ -o [^]mount-
options[,...] ] [ -r reserved-blocks-count ] [ -u user ] [ -g
group ] [ -C mount-count ] [ -E extended-options ] [ -L volume-
label ] [ -M last-mounted-directory ] [ -O [^]feature[,...] ] [
-Q quota-options ] [ -T time-last-checked ] [ -U UUID ] [ -z
undo_file ] device
tune2fs allows the system administrator to adjust various tunable
file system parameters on Linux ext2, ext3, or ext4 file systems.
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-label" or "UUID=uuid".
(i.e., LABEL=home or UUID=e40486c6-84d5-4f2f-b99c-032281799c9d).
-c max-mount-counts
Adjust the number of mounts after which the file system
will be checked by e2fsck(8). If max-mount-counts is the
string "random", tune2fs will use a random value between 20
and 40. If max-mount-counts is 0 or -1, the number of
times the file system is mounted will be disregarded by
e2fsck(8) and the kernel.
Staggering the mount-counts at which file systems are
forcibly checked will avoid all file systems being checked
at one time when using journaled file systems.
Mount-count-dependent checking is disabled by default to
avoid unanticipated long reboots while e2fsck does its
work. If you are concerned about file system corruptions
caused by potential hardware problems of kernel bugs, a
better solution than mount-count-dependent checking is to
use the e2scrub(8) program. This does require placing the
file system on an LVM volume, however.
-C mount-count
Set the number of times the file system 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
file system at the next reboot.
-e error-behavior
Change the behavior of the kernel code when errors are
detected. In all cases, a file system error will cause
e2fsck(8) to check the file system on the next boot.
error-behavior can be one of the following:
continue
Continue normal execution.
remount-ro
Remount file system read-only.
panic Cause a kernel panic.
-E extended-options
Set extended options for the file system. 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 file system corruption can
result. Needs '-f'.
encoding=encoding-name
Enable the casefold feature in the super block
and set encoding-name as the encoding to be
used. If encoding-name is not specified, utf8
is used. The encoding cannot be altered if
casefold was previously enabled.
encoding_flags=encoding-flags
Define parameters for file name character
encoding operations. If a flag is not changed
using this parameter, its default value is
used. encoding-flags should be a comma-
separated lists of flags to be enabled. The
flags cannot be altered if casefold was
previously enabled.
The only flag that can be set right now is
strict which means that invalid strings should
be rejected by the file system. In the default
configuration, the strict flag is disabled.
force_fsck
Set a flag in the file system superblock
indicating that errors have been found. This
will force fsck to run at the next mount.
hash_alg=hash-alg
Set the default hash algorithm used for file
systems with hashed b-tree directories. Valid
algorithms accepted are: legacy, half_md4, and
tea.
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.
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.
orphan_file_size=size
Set size of the file for tracking unlinked but
still open inodes and inodes with truncate in
progress. Larger file allows for better
scalability, reserving a few blocks per cpu is
ideal.
stride=stride-size
Configure the file system for a RAID array with
stride-size file system blocks. This is the
number of blocks read or written to disk before
moving to next disk. This mostly affects
placement of file system 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 file system for a RAID array with
stripe-width file system 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.
test_fs
Set a flag in the file system superblock
indicating that it may be mounted using
experimental kernel code, such as the ext4dev
file system.
^test_fs
Clear the test_fs flag, indicating the file
system should only be mounted using production-
level file system code.
-f Force the tune2fs operation to complete even in the face of
errors. This option is useful when removing the
has_journal file system feature from a file system 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 file system appears to
require journal replay, the -f flag must be specified twice
to proceed.
WARNING: Removing an external journal from a file system
which was not cleanly unmounted without first replaying the
external journal can result in severe data loss and file
system corruption.
-g group
Set the group which can use the reserved file system
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 file system 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.
There are pros and cons to disabling these periodic checks;
see the discussion under the -c (mount-count-dependent
check) option for details.
-I 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. Backing up the file system before changing inode
size is recommended.
File systems with an inode size of 128 bytes do not support
timestamps beyond January 19, 2038. Inodes which are 256
bytes or larger will support extended timestamps, project
id's, and the ability to store some extended attributes in
the inode table for improved performance.
-j Add an ext3 journal to the file system. 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 file system) stored within the file system.
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
file system, an immutable file, .journal, will be created
in the top-level directory of the file system, as it is the
only safe way to create the journal inode while the file
system is mounted. While the ext3 journal is visible, it
is not safe to delete it, or modify it while the file
system is mounted; for this reason the file is marked
immutable. While checking unmounted file systems,
e2fsck(8) will automatically move .journal files to the
invisible, reserved journal inode. For all file systems
except for the root file system, this should happen
automatically and naturally during the next reboot cycle.
Since the root file system 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 file system to ext3 if the /etc/fstab
file specifies the ext3 file system for the root file
system in order to avoid requiring the use of a rescue
floppy to add an ext3 journal to the root file system.
-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:
device=external-journal
Attach the file system 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 file systems which
will be using it. In addition, while there is
support for attaching multiple file systems 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).
fast_commit_size=fast-commit-size
Create an additional fast commit journal area
of size fast-commit-size kilobytes. This
option is only valid if fast_commit feature is
enabled on the file system. If this option is
not specified and if fast_commit feature is
turned on, fast commit area size defaults to
journal-size / 64 megabytes. The total size of
the journal with fast_commit feature set is
journal-size + ( fast-commit-size * 1024)
megabytes. The total journal size may be no
more than 10,240,000 file system blocks or half
the total file system size (whichever is
smaller).
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.
size=journal-size
Create a journal stored in the file system of
size journal-size megabytes. The size of the
journal must be at least 1024 file system
blocks (i.e., 1 MiB if using 1k blocks, 4 MiB
if using 4k blocks, etc.) and may be no more
than 10,240,000 file system blocks. There must
be enough free space in the file system to
create a journal of that size.
Only one of the size or device options can be given for a
file system.
-l List the contents of the file system superblock, including
the current values of the parameters that can be set via
this program.
-L volume-label
Set the volume label of the file system. Ext2 file system
labels can be at most 16 characters long; if volume-label
is longer than 16 characters, tune2fs will truncate it and
print a warning. For other file systems that support
online label manipulation and are mounted tune2fs will work
as well, but it will not attempt to truncate the volume-
label at all. 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 file system which may only be
allocated by privileged processes. Reserving some number
of file system blocks for use by privileged processes is
done to avoid file system 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 file system. Normally, the default
percentage of reserved blocks is 5%.
-M last-mounted-directory
Set the last-mounted directory for the file system.
-o [^]mount-option[,...]
Set or clear the indicated default mount options in the
file system. 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 file
system's superblock; mount options without a prefix
character or prefixed with a plus character ('+') will be
added to the file system.
The following mount options can be set or cleared using
tune2fs:
debug Enable debugging code for this file system.
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 file system is mounted with journaling
enabled, all data (not just metadata) is
committed into the journal prior to being
written into the main file system.
journal_data_ordered
When the file system is mounted with journaling
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 file system is mounted with journaling
enabled, data may be written into the main file
system 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 file system features (options)
in the file system. More than one file system feature can
be cleared or set by separating features with commas. File
System features prefixed with a caret character ('^') will
be cleared in the file system's superblock; file system
features without a prefix character or prefixed with a plus
character ('+') will be added to the file system. For a
detailed description of the file system features, please
see the man page ext4(5).
The following file system features can be set or cleared
using tune2fs:
64bit Enable the file system to be larger than 2^32
blocks.
casefold
Enable support for file system level
casefolding. The option can be cleared only if
filesystem has no directories with F attribute.
dir_index
Use hashed b-trees to speed up lookups for
large directories.
dir_nlink
Allow more than 65000 subdirectories per
directory.
ea_inode
Allow the value of each extended attribute to
be placed in the data blocks of a separate
inode if necessary, increasing the limit on the
size and number of extended attributes per
file. Tune2fs currently only supports setting
this file system feature.
encrypt
Enable support for file system level
encryption. Tune2fs currently only supports
setting this file system feature.
extent Enable the use of extent trees to store the
location of data blocks in inodes. Tune2fs
currently only supports setting this file
system feature.
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 file system consistency
even across unclean shutdowns. Setting the
file system feature is equivalent to using the
-j option.
fast_commit
Enable fast commit journaling feature to
improve fsync latency.
large_dir
Increase the limit on the number of files per
directory. Tune2fs currently only supports
setting this file system feature.
huge_file
Support files larger than 2 terabytes in size.
large_file
File System can contain files that are greater
than 2 GiB.
metadata_csum
Store a checksum to protect the contents in
each metadata block.
metadata_csum_seed
Allow the file system to store the metadata
checksum seed in the superblock, enabling the
administrator to change the UUID of a file
system using the metadata_csum feature while it
is mounted.
mmp Enable or disable multiple mount protection
(MMP) feature.
orphan_file
Store the list of orphan inodes in multiple
blocks instead of a single linked-list to avoid
potential scalability bottlenecks for workloads
that perform a large number of file truncations
or extensions in parallel.
project
Enable project ID tracking. This is used for
project quota tracking.
quota Enable internal file system quota inodes.
read-only
Force the kernel to mount the file system read-
only.
resize_inode
Reserve space so the block group descriptor
table may grow in the future. Tune2fs only
supports clearing this file system feature.
sparse_super
Limit the number of backup superblocks to save
space on large file systems. Tune2fs currently
only supports setting this file system feature.
stable_inodes
Prevent the file system from being shrunk or
having its UUID changed, in order to allow the
use of specialized encryption settings that
make use of the inode numbers and UUID.
Tune2fs currently only supports setting this
file system feature.
uninit_bg
Allow the kernel to initialize bitmaps and
inode tables lazily, and to keep a high
watermark for the unused inodes in a file
system, 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 is.
verity Enable support for verity protected files.
Tune2fs currently only supports setting this
file system feature.
After setting or clearing sparse_super, uninit_bg,
filetype, or resize_inode file system features, the file
system may require being checked using e2fsck(8) to return
the file system 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
file system features may prevent the file system 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 file system.
-r reserved-blocks-count
Set the number of reserved file system 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.
[^]prjquota
Sets/clears project quota inode in the
superblock.
-T time-last-checked
Set the time the file system 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 file system, and
then check the file system during off hours to make sure it
hasn't been corrupted due to hardware problems, etc. If
the file system was clean, then this option can be used to
set the last checked time on the original file system. 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 file system 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 file
system 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 file system 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.
-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 crash.
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
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>.
tune2fs is part of the e2fsprogs package and is available from
http://e2fsprogs.sourceforge.net.
debugfs(8), dumpe2fs(8), e2fsck(8), mke2fs(8), ext4(5)
This page is part of the e2fsprogs (utilities for ext2/3/4
filesystems) project. Information about the project can be found
at ⟨http://e2fsprogs.sourceforge.net/⟩. It is not known how to
report bugs for this man page; if you know, please send a mail to
man-pages@man7.org. This page was obtained from the project's
upstream Git repository
⟨git://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git⟩ on
2025-08-11. (At that time, the date of the most recent commit
that was found in the repository was 2025-07-31.) If you discover
any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page,
or you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a
mail to man-pages@man7.org
E2fsprogs version 1.47.3 July 2025 TUNE2FS(8)
Pages that refer to this page: ext4(5), mke2fs.conf(5), debugfs(8), dumpe2fs(8), e2fsck(8), e2label(8), e2undo(8), fsadm(8), mke2fs(8), mount(8), tune2fs(8)
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