tune2fs(8) — Linux manual page


TUNE2FS(8)                 System Manager's Manual                TUNE2FS(8)

NAME         top

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

SYNOPSIS         top

       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         top

       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         top

       -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
              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.
              However, you may wish to 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 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.

       -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:

                          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 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 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

                          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 errors have been found.  This will force fsck
                          to run at the next mount.

                          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
              journal (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

       -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
              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.

              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 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
              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 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:

                          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.

                          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.

                          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 currently support shared external journals

                          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

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

       -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 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

       -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 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%.

       -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
              filesystem.  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 feature; in particular, kernels which predate 2.4.20 will
              almost certainly ignore the default mount options field in the

              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

              The following mount options can be set or cleared using

                   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

                          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.

                          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 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
                          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.)

                          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.)

       -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 system features, please see the man page ext4(5).

              The following filesystem features can be set or cleared using

                   64bit  Enable the file system to be larger than 2^32

                          Use hashed b-trees to speed up lookups for large

                          Allow more than 65000 subdirectories per

                          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 filesystem

                          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

                          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 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.

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

                          Increase the limit on the number of files per
                          directory.  Tune2fs currently only supports
                          setting this filesystem feature.

                          Support files larger than 2 terabytes in size.

                          Filesystem can contain files that are greater than

                          Store a checksum to protect the contents in each
                          metadata block.

                          Allow the filesystem to store the metadata
                          checksum seed in the superblock, enabling the
                          administrator to change the UUID of a filesystem
                          using the metadata_csum feature while it is

                   mmp    Enable or disable multiple mount protection (MMP)

                          Enable project ID tracking.  This is used for
                          project quota tracking.

                   quota  Enable internal file system quota inodes.

                          Force the kernel to mount the file system read-

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

                          Limit the number of backup superblocks to save
                          space on large filesystems.  Tune2fs currently
                          only supports setting this filesystem feature.

                          Prevent the filesystem 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 filesystem feature.

                          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.  The 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.

                   verity Enable support for verity protected files.
                          Tune2fs currently only supports setting this
                          filesystem feature.

              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 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.

       -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.

                          Sets/clears group quota inode in the superblock.

                          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 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 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
              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 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         top

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

AUTHOR         top

       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 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         top

       tune2fs is part of the e2fsprogs package and is available from

SEE ALSO         top

       debugfs(8), dumpe2fs(8), e2fsck(8), mke2fs(8), ext4(5)

COLOPHON         top

       This page is part of the e2fsprogs (utilities for ext2/3/4
       filesystems) project.  Information about the project can be found at
       ⟨http://e2fsprogs.sourceforge.net/⟩.  It is not known how to report
       bugs for this man page; if you know, please send a mail to
       man-pages@man7.org.  This page was obtained from the project's up‐
       stream Git repository
       ⟨git://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git⟩ on 2020-11-01.
       (At that time, the date of the most recent commit that was found in
       the repository was 2020-10-01.)  If you discover any rendering prob‐
       lems in this HTML version of the page, or you believe there is a bet‐
       ter or more up-to-date source for the page, or you have corrections
       or improvements to the information in this COLOPHON (which is not
       part of the original manual page), send a mail to man-pages@man7.org

E2fsprogs version 1.46-WIP       March 2020                       TUNE2FS(8)

Pages that refer to this page: ext2(5)ext3(5)ext4(5)mke2fs.conf(5)debugfs(8)dumpe2fs(8)e2fsck(8)e2label(8)e2undo(8)fsadm(8)mke2fs(8)mount(8)tune2fs(8)