TUNE2FS(8) System Manager's Manual TUNE2FS(8)
NAME
tune2fs - adjust tunable filesystem parameters on ext2/ext3/ext4
filesystems
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
filesystem parameters on Linux ext2, ext3, or ext4 filesystems. 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 filesystem 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 filesystem
is mounted will be disregarded by e2fsck(8) and the kernel.
Staggering the mount-counts at which filesystems are forcibly
checked will avoid all filesystems being checked at one time
when using journaled filesystems.
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 filesystem has been mounted. If set
to a greater value than the max-mount-counts parameter set by
the -c option, e2fsck(8) will check the filesystem at the next
reboot.
-e error-behavior
Change the behavior of the kernel code when errors are detected.
In all cases, a filesystem error will cause e2fsck(8) to check
the filesystem on the next boot. error-behavior can be one of
the following:
continue Continue normal execution.
remount-ro Remount filesystem read-only.
panic Cause a kernel panic.
-E extended-options
Set extended options for the filesystem. Extended options are
comma separated, and may take an argument using the equals ('=')
sign. The following extended options are supported:
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
filesystem 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 interval must
be less than 300 seconds. Requires that the mmp
feature be enabled.
stride=stride-size
Configure the filesystem for a RAID array with
stride-size filesystem blocks. This is the number of
blocks read or written to disk before moving to next
disk. This mostly affects placement of filesystem
metadata like bitmaps at mke2fs(2) time to avoid
placing them on a single disk, which can hurt the
performance. It may also be used by block alloca-
tor.
stripe_width=stripe-width
Configure the filesystem for a RAID array with
stripe-width filesystem blocks per stripe. This is
typically be stride-size * N, where N is the number
of data disks in the RAID (e.g. RAID 5 N+1, RAID 6
N+2). This allows the block allocator to prevent
read-modify-write of the parity in a RAID stripe if
possible when the data is written.
hash_alg=hash-alg
Set the default hash algorithm used for filesystems
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 previ-
ously 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.
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 op-
tions 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 filesystem superblock indicating
that errors have been found. This will force fsck
to run at the next mount.
test_fs
Set a flag in the filesystem superblock indicating
that it may be mounted using experimental kernel
code, such as the ext4dev filesystem.
^test_fs
Clear the test_fs flag, indicating the filesystem
should only be mounted using production-level
filesystem code.
-f Force the tune2fs operation to complete even in the face of er-
rors. This option is useful when removing the has_journal
filesystem feature from a filesystem which has an external jour-
nal (or is corrupted such that it appears to have an external
journal), but that external journal is not available. If the
filesystem appears to require journal replay, the -f flag must
be specified twice to proceed.
WARNING: Removing an external journal from a filesystem which
was not cleanly unmounted without first replaying the external
journal can result in severe data loss and filesystem corrup-
tion.
-g group
Set the group which can use the reserved filesystem blocks. The
group parameter can be a numerical gid or a group name. If a
group name is given, it is converted to a numerical gid before
it is stored in the superblock.
-i interval-between-checks[d|m|w]
Adjust the maximal time between two filesystem 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 opera-
tion can also take a while and the file system can be corrupted
and data lost if it is interrupted while in the middle of con-
verting 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 filesystem. If the -J option is not
specified, the default journal parameters will be used to create
an appropriately sized journal (given the size of the filesys-
tem) stored within the filesystem. Note that you must be using
a kernel which has ext3 support in order to actually make use of
the journal.
If this option is used to create a journal on a mounted filesys-
tem, an immutable file, .journal, will be created in the top-
level directory of the filesystem, as it is the only safe way to
create the journal inode while the filesystem is mounted. While
the ext3 journal is visible, it is not safe to delete it, or
modify it while the filesystem is mounted; for this reason the
file is marked immutable. While checking unmounted filesystems,
e2fsck(8) will automatically move .journal files to the invisi-
ble, reserved journal inode. For all filesystems except for the
root filesystem, this should happen automatically and naturally
during the next reboot cycle. Since the root filesystem is
mounted read-only, e2fsck(8) must be run from a rescue floppy in
order to effect this transition.
On some distributions, such as Debian, if an initial ramdisk is
used, the initrd scripts will automatically convert an ext2 root
filesystem to ext3 if the /etc/fstab file specifies the ext3
filesystem for the root filesystem in order to avoid requiring
the use of a rescue floppy to add an ext3 journal to the root
filesystem.
-J journal-options
Override the default ext3 journal parameters. Journal options
are comma separated, and may take an argument using the equals
('=') sign. The following journal options are supported:
size=journal-size
Create a journal stored in the filesystem of size
journal-size megabytes. The size of the journal
must be at least 1024 filesystem blocks (i.e., 1MB
if using 1k blocks, 4MB if using 4k blocks, etc.)
and may be no more than 10,240,000 filesystem
blocks. There must be enough free space in the
filesystem to create a journal of that size.
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 filesystem 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.
device=external-journal
Attach the filesystem to the journal block device
located on external-journal. The external journal
must have been already created using the command
mke2fs -O journal_dev external-journal
Note that external-journal must be formatted with
the same block size as filesystems which will be us-
ing it. In addition, while there is support for at-
taching multiple filesystems to a single external
journal, the Linux kernel and e2fsck(8) do not cur-
rently support shared external journals yet.
Instead of specifying a device name directly, exter-
nal-journal can also be specified by either LA-
BEL=label or UUID=UUID to locate the external jour-
nal 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).
Only one of the size or device options can be given for a
filesystem.
-l List the contents of the filesystem 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 filesystem. Ext2 filesystem labels
can be at most 16 characters long; if volume-label is longer
than 16 characters, tune2fs will truncate it and print a warn-
ing. 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 filesystem which may only be allocated
by privileged processes. Reserving some number of filesystem
blocks for use by privileged processes is done to avoid filesys-
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 filesystem. Nor-
mally, the default percentage of reserved blocks is 5%.
-M last-mounted-directory
Set the last-mounted directory for the filesystem.
-o [^]mount-option[,...]
Set or clear the indicated default mount options in the filesys-
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 cer-
tainly 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 filesystem's superblock;
mount options without a prefix character or prefixed with a plus
character ('+') will be added to the filesystem.
The following mount options can be set or cleared using tune2fs:
debug Enable debugging code for this filesystem.
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 direc-
tory 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
expect 16-bit values.
journal_data
When the filesystem is mounted with journalling en-
abled, all data (not just metadata) is committed
into the journal prior to being written into the
main filesystem.
journal_data_ordered
When the filesystem is mounted with journalling 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 filesystem is mounted with journalling en-
abled, data may be written into the main filesystem
after its metadata has been committed to the jour-
nal. 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_va-
lidity 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 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-provi-
sioned drives available in some enterprise storage
arrays) to inform the storage device that blocks be-
longing 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+
kernels.)
-O [^]feature[,...]
Set or clear the indicated filesystem features (options) in the
filesystem. More than one filesystem feature can be cleared or
set by separating features with commas. Filesystem features
prefixed with a caret character ('^') will be cleared in the
filesystem's superblock; filesystem features without a prefix
character or prefixed with a plus character ('+') will be added
to the filesystem. For a detailed description of the file sys-
tem features, please see the man page ext4(5).
The following filesystem 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
filesystem feature.
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
necessary, increasing the limit on the size and num-
ber of extended attributes per file. Tune2fs cur-
rently only supports setting this filesystem fea-
ture.
encrypt
Enable support for file system level encryption.
Tune2fs currently only supports setting this
filesystem feature.
extent Enable the use of extent trees to store the location
of data blocks in inodes. Tune2fs currently only
supports setting this filesystem 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 filesystem consistency even
across unclean shutdowns. Setting the filesystem
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
filesystem feature.
huge_file
Support files larger than 2 terabytes in size.
large_file
Filesystem 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 filesystem to store the metadata checksum
seed in the superblock, enabling the administrator
to change the UUID of a filesystem using the meta-
data_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 future. Tune2fs only supports
clearing this filesystem feature.
sparse_super
Limit the number of backup superblocks to save space
on large filesystems. Tune2fs currently only sup-
ports setting this filesystem feature.
stable_inodes
Prevent the filesystem from being shrunk or having
its UUID changed, in order to allow the use of spe-
cialized encryption settings that make use of the
inode numbers and UUID. Tune2fs currently only sup-
ports setting this filesystem feature.
uninit_bg
Allow the kernel to initialize bitmaps and inode ta-
bles lazily, and to keep a high watermark for the
unused inodes in a filesystem, to reduce e2fsck(8)
time. The first e2fsck run after enabling this 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 filesystem fea-
ture.
After setting or clearing sparse_super, uninit_bg, filetype, or
resize_inode filesystem features, the file system may require
being checked using e2fsck(8) to return the filesystem to a 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
filesystem features may prevent the filesystem 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 filesystem.
-r reserved-blocks-count
Set the number of reserved filesystem blocks.
-Q quota-options
Sets 'quota' feature on the superblock and works on the quota
files for the given quota type. Quota options could be one or
more of the 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 filesystem was last checked using e2fsck. The
time is interpreted using the current (local) timezone. This
can be useful in scripts which use a Logical Volume Manager to
make a consistent snapshot of a filesystem, and then check the
filesystem during off hours to make sure it hasn't been cor-
rupted due to hardware problems, etc. If the filesystem was
clean, then this option can be used to set the last checked time
on the original filesystem. The format of time-last-checked is
the international date format, with an optional time specifier,
i.e. YYYYMMDD[HH[MM[SS]]]. The keyword now is also accepted,
in which case the last checked time will be set to the current
time.
-u user
Set the user who can use the reserved filesystem blocks. user
can be a numerical uid or a user name. If a user name is given,
it is converted to a numerical uid before it is stored in the
superblock.
-U UUID
Set the universally unique identifier (UUID) of the filesystem
to UUID. The format of the UUID is a series of hex digits sepa-
rated by hyphens, like this:
"c1b9d5a2-f162-11cf-9ece-0020afc76f16". The UUID parameter may
also be one of the following:
clear clear the filesystem 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 cur-
rently 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 1.46.2 February 2021 TUNE2FS(8)
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