TUNE2FS(8) System Manager's Manual TUNE2FS(8)
NAME
tune2fs - adjust tunable file system parameters on ext2/ext3/ext4 file
systems
SYNOPSIS
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
DESCRIPTION
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).
OPTIONS
-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.
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)
E2fsprogs version 1.47.3 July 2025 TUNE2FS(8)
tune2fs \- adjust tunable file system parameters on ext2/ext3/ext4 file systems