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)

       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-

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 the
              string "random", tune2fs will use a random value between
              20 and 40.  If max-mount-counts is 0 or -1, the number of
              times the 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 normal execution.

                          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

                          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

                          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

                          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.

                          Enable the casefold feature in the super block
                          and set encoding-name as the encoding to be
                          used.  If encoding-name is not specified, utf8
                          is used. The encoding cannot be altered if
                          casefold was previously enabled.

                          Define parameters for file name character
                          encoding operations.  If a flag is not changed
                          using this parameter, its default value is
                          used.  encoding-flags should be a comma-
                          separated lists of flags to be enabled.  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

                          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)

                          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

                          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

              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.

       -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

              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.

                          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

                          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 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

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

       -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 /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 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 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

                   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 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 tune2fs:

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

                          Enable support for file system level
                          casefolding.  Tune2fs currently only supports
                          setting this filesystem feature.

                          Use hashed b-trees to speed up lookups for
                          large directories.

                          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 feature.

                          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.

                          Enable the extended inode fields used by ext4.

                          Store file type information in directory

                          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

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

                          Enable fast commit journaling feature to
                          improve fsync latency.

                          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 2GB.

                          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 mounted.

                   mmp    Enable or disable multiple mount protection
                          (MMP) feature.

                          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

                          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

                   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

                          Sets/clears group quota inode in the

                          Sets/clears project 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 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

              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

       -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

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
       upstream Git repository
       ⟨git://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git⟩ on
       2021-04-01.  (At that time, the date of the most recent commit
       that was found in the repository was 2021-02-28.)  If you
       discover any rendering problems in this HTML version of the page,
       or you believe there is a better 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 1.46.2      February 2021                   TUNE2FS(8)

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