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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-be-
tween-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) pro-
gram.
The device specifier can either be a filename (i.e., /dev/sda1), or a LABEL or UUID speci-
fier: "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 corrup-
tions 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 op-
tions are supported:
clear_mmp
Reset the MMP block (if any) back to the clean state. Use only if ab-
solutely certain the device is not currently mounted or being fscked,
or major file system corruption can result. Needs '-f'.
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 in-
terval must be less than 300 seconds. Requires that the mmp feature be
enabled.
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 meta-
data 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 al-
locator.
stripe_width=stripe-width
Configure the file system for a RAID array with stripe-width file sys-
tem 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.
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.
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 en-
abled.
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 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 in-
valid strings should be rejected by the file system. In the default
configuration, the strict flag is disabled.
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.
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.
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 sys-
tem.
^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 un-
mounted 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 inter-
pret 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 un-
der 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 cor-
rupted 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 Janu-
ary 19, 2038. Inodes which are 256 bytes or larger will support extended time-
stamps, project id's, and the ability to store some extended attributes in the in-
ode table for improved performance.
-j Add an ext3 journal to the file system. If the -J option is not specified, the de-
fault 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 op-
tions are supported:
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., 1MB if using 1k blocks, 4MB 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.
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 be-
ginning of the file system.
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 jour-
nal, the Linux kernel and e2fsck(8) do not currently support shared ex-
ternal 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 su-
perblock 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 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 trun-
cate 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 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 pro-
cesses is done to avoid file system fragmentation, and to allow system daemons,
such as syslogd(8), to continue to function correctly after non-privileged pro-
cesses are prevented from writing to the file system. Normally, the default per-
centage 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 fea-
ture; 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 com-
mas. 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 stor-
age 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 com-
mas. 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 de-
tailed 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. Tune2fs currently
only supports setting this file system feature.
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 fea-
ture.
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 cre-
ates 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 cur-
rently 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 2GB.
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 su-
perblock, enabling the administrator to change the UUID of a file sys-
tem using the metadata_csum feature while it is mounted.
mmp Enable or disable multiple mount protection (MMP) feature.
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 fu-
ture. Tune2fs only supports clearing this file system feature.
sparse_super
Limit the number of backup superblocks to save space on large file sys-
tems. Tune2fs currently only supports setting this file system fea-
ture.
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 frac-
tion of the original time, depending on how full the file system is.
verity Enable support for verity protected files. Tune2fs currently only sup-
ports 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 re-
turn the file system to a consistent state. Tune2fs will print a message request-
ing 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 par-
ticular, 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 inter-
preted 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 for-
mat 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-de-
vice.e2undo in the directory specified via the E2FSPROGS_UNDO_DIR environment vari-
able.
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 AT linux.org>. It is currently being maintained
by Theodore Ts'o <tytso AT alum.edu>. tune2fs uses the ext2fs library written by
Theodore Ts'o <tytso AT mit.edu>. This manual page was written by Christian Kuhtz <chk@data-
hh.Hanse.DE>. Time-dependent checking was added by Uwe Ohse <uwe AT tirka.de>.
AVAILABILITY
tune2fs is part of the e2fsprogs package and is available from http://e2fsprogs.source-
forge.net.
SEE ALSO
debugfs(8), dumpe2fs(8), e2fsck(8), mke2fs(8), ext4(5)
E2fsprogs version 1.46.5 December 2021 TUNE2FS(8)
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