tune2fs - adjust tunable filesystem parameters on ext2/ext3/ext4 filesystems

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tune2fs - adjust tunable filesystem parameters on ext2/ext3/ext4

tune2fs [ -l ] [ -c max-mount-counts ] [ -e errors-behavior ] [ -f ] [
-i interval-between-checks ] [ -j ] [ -J journal-options ] [ -m
reserved-blocks-percentage ] [ -o [^]mount-options[,...] ] [ -r
reserved-blocks-count ] [ -s sparse-super-flag ] [ -u user ] [ -g group
] [ -C mount-count ] [ -E extended-options ] [ -L volume-name ] [ -M
last-mounted-directory ] [ -O [^]feature[,...] ] [ -Q quota-options ]
[ [ -T time-last-checked ] [ -U UUID ] device

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 specifer can either be a filename (i.e., /dev/sda1), or a
LABEL or UUID specifer: "LABEL=volume-name" or "UUID=uuid". (i.e.,
LABEL=home or UUID=e40486c6-84d5-4f2f-b99c-032281799c9d).

-c max-mount-counts
Adjust the number of mounts after which the filesystem will be
checked by e2fsck(8). If max-mount-counts is 0 or -1, the num‐
ber 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.

You should strongly consider the consequences of disabling
mount-count-dependent checking entirely. Bad disk drives,
cables, memory, and kernel bugs could all corrupt a filesystem
without marking the filesystem dirty or in error. If you are
using journaling on your filesystem, your filesystem will never
be marked dirty, so it will not normally be checked. A filesys‐
tem error detected by the kernel will still force an fsck on the
next reboot, but it may already be too late to prevent data loss
at that point.

See also the -i option for time-dependent checking.

-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

-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:

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'.

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.

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‐

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.

Set the default hash algorithm used for filesystems
with hashed b-tree directories. Valid algorithms
accepted are: legacy, half_md4, and tea.

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.

Set a flag in the filesystem superblock indicating
that it may be mounted using experimental kernel
code, such as the ext4dev filesystem.

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
errors. 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.

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‐

-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.

It is strongly recommended that either -c (mount-count-depen‐
dent) or -i (time-dependent) checking be enabled to force peri‐
odic full e2fsck(8) checking of the filesystem. Failure to do
so may lead to filesystem corruption (due to bad disks, cables,
memory, or kernel bugs) going unnoticed, ultimately resulting in
data loss or corruption.

-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

-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:

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 102,400 filesystem blocks.
There must be enough free space in the filesystem to
create a journal of that size.

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
using it. In addition, while there is support for
attaching 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
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

Only one of the size or device options can be given for a

-l List the contents of the filesystem superblock, including the
current values of the parameters that can be set via this pro‐

-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=vol‐
ume_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.

Emulate BSD behaviour when creating new files: they
will take the group-id of the directory in which
they were created. The standard System V behaviour
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.

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.

When the filesystem is mounted with journalling
enabled, all data (not just metadata) is committed
into the journal prior to being written into the
main filesystem.

When the filesystem is mounted with journalling
enabled, all data is forced directly out to the main
file system prior to its metadata being committed to
the journal.

When the filesystem is mounted with journalling
enabled, data may be written into the main filesys‐
tem 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.

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.)

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 overwrit‐
ing parts of the inode table or block group descrip‐
tors. This comes at the cost of increased memory
and CPU overhead, so it is enabled only for debug‐
ging purposes. (This option is currently only sup‐
ported by the ext4 file system driver in 2.6.35+

The file system will be mouinted 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
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.)

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+

-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.

The following filesystem features can be set or cleared using

Use hashed b-trees to speed up lookups in large

Allow more than 65000 subdirectories per directory.

Store file type information in directory entries.

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 formated file system with flex_bg

Use a journal to ensure filesystem consistency even
across unclean shutdowns. Setting the filesystem
feature is equivalent to using the -j option.

Filesystem can contain files that are greater than
2GB. (Modern kernels set this feature automatically
when a file > 2GB is created.)

Reserve space so the block group descriptor table
may grow in the future. Tune2fs only supports
clearing this filesystem feature.

mmp Enable or disable multiple mount protection (MMP)
feature. MMP helps to protect the filesystem from
being multiply mounted and is useful in shared stor‐
age environments.

Limit the number of backup superblocks to save space
on large filesystems.

Allow the kernel to initialize bitmaps and inode
tables and keep a high watermark for the unused
inodes in a filesystem, to reduce e2fsck(8) time.
This 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.

After setting or clearing sparse_super, uninit_bg, filetype, or
resize_inode filesystem features, e2fsck(8) must be run on the
filesystem to return the filesystem to a consistent state.
Tune2fs will print a message requesting that the system adminis‐
trator 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 particular, the uninit_bg and
flex_bg features are only supported by the ext4 filesystem.

-p mmp_check_interval
Set the desired MMP check interval in seconds. It is 5 seconds
by default.

-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:

Sets/clears user quota inode in the superblock.
[^]usrquota Sets/clears group quota inode in the

-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 consis‐
tent snapshot of a filesystem, and then check the
filesystem during off hours to make sure it hasn't
been corrupted 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 numer‐
ical uid before it is stored in the superblock.

Set the universally unique identifier (UUID) of the
filesystem 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 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 automati‐
cally use a time-based UUID instead of a randomly-
generated UUID.

We haven't found any bugs yet. That doesn't mean there aren't any...

tune2fs was written by Remy Card . It is cur‐
rently being maintained by Theodore Ts'o . tune2fs
uses the ext2fs library written by Theodore Ts'o . This
manual page was written by Christian Kuhtz .
Time-dependent checking was added by Uwe Ohse .

tune2fs is part of the e2fsprogs package and is available from

debugfs(8), dumpe2fs(8), e2fsck(8), mke2fs(8)

E2fsprogs version 1.42 November 2011 TUNE2FS(8)