TUNE2FS(8) System Manager's Manual TUNE2FS(8)
tune2fs - adjust tunable filesystem parameters on ext2/ext3/ext4 filesystems
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 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-name" or "UUID=uuid". (i.e.,
LABEL=home or UUID=e40486c6-84d5-4f2f-b99c-032281799c9d).
Adjust the number of mounts after which the filesystem will be checked by e2fsck(8). 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.
You should strongly consider the consequences of disabling mount-count-dependent checking entirely. Bad disk drives, cables, mem-
ory, 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 filesystem 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.
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.
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.
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 inter-
val. 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 writ-
ten 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 allocator.
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 alloca-
tor 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
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 journal (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 corruption.
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.
Adjust the maximal time between two filesystem 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.
It is strongly recommended that either -c (mount-count-dependent) or -i (time-dependent) checking be enabled to force periodic full
e2fsck(8) checking of the filesystem. Failure to do so may lead to filesystem corruption (due to bad disks, cables, memory, or ker-
nel 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 filesystem) 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 filesystem, 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 invisible, reserved jour-
nal 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
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.
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 addi-
tion, while there is support for attaching multiple filesystems 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).
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 program.
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 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.
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 filesystem 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 filesystem. Normally, the
default percentage of reserved blocks is 5%.
Set the last-mounted directory for the filesystem.
Set or clear the indicated default mount options in the filesystem. Default mount options can be overridden by mount options speci-
fied either in /etc/fstab(5) or on the command line arguments to mount(8). Older kernels may not support this feature; in particu-
lar, 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 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 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.
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 val-
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 filesystem 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 operations in the journal disabled. (This option is currently only sup-
ported 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
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 sys-
tem driver in 2.6.35+ kernels.)
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.)
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.)
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 system features, please see the man page ext4(5).
The following filesystem features can be set or cleared using tune2fs:
Use hashed b-trees to speed up lookups for large directories.
Allow more than 65000 subdirectories per directory.
extent Enable the use of extent trees to store the location of data blocks in inodes.
Enable the extended inode fields used by ext4.
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 reorga-
nize 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.
Use a journal to ensure filesystem consistency even across unclean shutdowns. Setting the filesystem feature is equiva-
lent to using the -j option.
Support files larger than 2 terabytes in size.
Filesystem can contain files that are greater than 2GB.
Reserve space so the block group descriptor table may grow in the future. Tune2fs only supports clearing this filesys-
mmp Enable or disable multiple mount protection (MMP) feature.
Limit the number of backup superblocks to save space on large filesystems.
Allow the kernel to initialize bitmaps and inode tables lazily, and to 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 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 particular, the uninit_bg and flex_bg features are only supported by the ext4 filesystem.
Set the desired MMP check interval in seconds. It is 5 seconds by default.
Set the number of reserved filesystem blocks.
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
Sets/clears user quota inode in the superblock.
Sets/clears group quota inode in the superblock.
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 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 for-
mat, 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.
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.
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 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.
We haven't found any bugs yet. That doesn't mean there aren't any...
tune2fs was written by Remy Card <Remy.Card@linux.org>. It is currently being maintained by Theodore Ts'o <email@example.com>. tune2fs
uses the ext2fs library written by Theodore Ts'o <firstname.lastname@example.org>. This manual page was written by Christian Kuhtz <chk@data-hh.Hanse.DE>.
Time-dependent checking was added by Uwe Ohse <email@example.com>.
tune2fs is part of the e2fsprogs package and is available from http://e2fsprogs.sourceforge.net.
debugfs(8), dumpe2fs(8), e2fsck(8), mke2fs(8), ext4(5)
E2fsprogs version 1.42.9 December 2013 TUNE2FS(8)