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

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

       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

       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).

       -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

       -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

                          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 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.

       -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

       -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 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

              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 /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

              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 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+

                          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+

                          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+

       -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 directory.

                          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 feature.

                          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

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

                          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 mounted.

                   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-only.

                          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.

                          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

              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

       -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

       -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.

       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 <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

       tune2fs is part of the e2fsprogs package and is available from

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

E2fsprogs version 1.45.5         January 2020                       TUNE2FS(8)