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-direc-
tory ] [ -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 cur-
rent 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 "ran-
dom", 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 re-
boot.
-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 cur-
rently 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 en-
coding-name is not specified, utf8 is used. The en-
coding 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 pa-
rameter, its default value is used. encoding-flags
should be a comma-separated lists of flags to be en-
abled. 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 ac-
cepted 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 arbi-
trary string with a maximum length of 63 bytes, which
is stored in the superblock.
The ext4 file system driver will first apply the bit-
mask-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 er-
rors. 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 jour-
nal), 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 corrup-
tion.
-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 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.
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 in-
ode size is recommended.
File systems with an inode size of 128 bytes do not support time-
stamps 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 sys-
tem) 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 sys-
tem, 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 mod-
ify 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 invisi-
ble, 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 attach-
ing multiple file systems to a single external jour-
nal, the Linux kernel and e2fsck(8) do not currently
support shared external journals yet.
Instead of specifying a device name directly, exter-
nal-journal can also be specified by either LABEL=la-
bel 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 la-
bel 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 to-
tal 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 pro-
gram.
-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 sys-
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 file system. Nor-
mally, 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 sys-
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 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 char-
acter ('^') 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 interop-
erability with older kernels which only store and ex-
pect 16-bit values.
journal_data
When the file system is mounted with journaling en-
abled, 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 en-
abled, 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 en-
abled, 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 opera-
tions in the journal disabled. (This option is cur-
rently only supported by the ext4 file system driver
in 2.6.35+ kernels.)
block_validity
The file system will be mounted with the block_valid-
ity option enabled, which causes extra checks to be
performed after reading or writing from the file sys-
tem. 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 over-
head, 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 alloca-
tion feature. (This option is currently only sup-
ported by the ext4 file system driver in 2.6.35+ ker-
nels.)
-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 char-
acter 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 di-
rectories.
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 nec-
essary, 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 direc-
tory. 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 meta-
data_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 sup-
ports 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 spe-
cialized encryption settings that make use of the in-
ode numbers and UUID. Tune2fs currently only sup-
ports setting this file system feature.
uninit_bg
Allow the kernel to initialize bitmaps and inode ta-
bles lazily, and to keep a high watermark for the un-
used inodes in a file system, to reduce e2fsck(8)
time. The first e2fsck run after enabling this fea-
ture 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 fea-
ture.
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 con-
sistent 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 orig-
inal file system. The format of time-last-checked is the inter-
national 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 su-
perblock.
-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 sepa-
rated 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 spe-
cial 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/uran-
dom, 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 man-
ual 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 1.47.2 January 2025 TUNE2FS(8)
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