mke2fs(8) — Linux manual page


MKE2FS(8)                System Manager's Manual               MKE2FS(8)

NAME         top

       mke2fs - create an ext2/ext3/ext4 file system

SYNOPSIS         top

       mke2fs [ -c | -l filename ] [ -b block-size ] [ -C cluster-size ]
       [ -d root-directory|tarball ] [ -D ] [ -g blocks-per-group ] [ -G
       number-of-groups ] [ -i bytes-per-inode ] [ -I inode-size ] [ -j
       ] [ -J journal-options ] [ -N number-of-inodes ] [ -n ] [ -m
       reserved-blocks-percentage ] [ -o creator-os ] [ -O
       [^]feature[,...]  ] [ -q ] [ -r fs-revision-level ] [ -E
       extended-options ] [ -v ] [ -F ] [ -L volume-label ] [ -M last-
       mounted-directory ] [ -S ] [ -t fs-type ] [ -T usage-type ] [ -U
       UUID ] [ -V ] [ -e errors-behavior ] [ -z undo_file ] device [
       fs-size ]

       mke2fs -O journal_dev [ -b block-size ] [ -L volume-label ] [ -n
       ] [ -q ] [ -v ] external-journal [ fs-size ]

DESCRIPTION         top

       mke2fs is used to create an ext2, ext3, or ext4 file system,
       usually in a disk partition (or file) named by device.

       The file system size is specified by fs-size.  If fs-size does
       not have a suffix, it is interpreted as power-of-two kilobytes,
       unless the -b blocksize option is specified, in which case fs-
       size is interpreted as the number of blocksize blocks.   If the
       fs-size is suffixed by 'k', 'm', 'g', 't' (either upper-case or
       lower-case), then it is interpreted in power-of-two kilobytes,
       megabytes, gigabytes, terabytes, etc.  If fs-size is omitted,
       mke2fs will create the file system based on the device size.

       If mke2fs is run as mkfs.XXX (i.e., mkfs.ext2, mkfs.ext3, or
       mkfs.ext4) the option -t XXX is implied; so mkfs.ext3 will create
       a file system for use with ext3, mkfs.ext4 will create a file
       system for use with ext4, and so on.

       The defaults of the parameters for the newly created file system,
       if not overridden by the options listed below, are controlled by
       the /etc/mke2fs.conf configuration file.  See the mke2fs.conf(5)
       manual page for more details.

OPTIONS         top

       -b block-size
              Specify the size of blocks in bytes.  Valid block-size
              values are powers of two from 1024 up to 65536 (however
              note that the kernel is able to mount only file systems
              with block-size smaller or equal to the system page size -
              4k on x86 systems, up to 64k on ppc64 or aarch64 depending
              on kernel configuration).  If omitted, block-size is
              heuristically determined by the file system size and the
              expected usage of the file system (see the -T option).  In
              most common cases, the default block size is 4k. If block-
              size is preceded by a negative sign ('-'), then mke2fs
              will use heuristics to determine the appropriate block
              size, with the constraint that the block size will be at
              least block-size bytes.  This is useful for certain
              hardware devices which require that the blocksize be a
              multiple of 2k.

       -c     Check the device for bad blocks before creating the file
              system.  If this option is specified twice, then a slower
              read-write test is used instead of a fast read-only test.

       -C  cluster-size
              Specify the size of cluster in bytes for file systems
              using the bigalloc feature.  Valid cluster-size values
              range from 2 to 32768 times the filesystem blocksize and
              must be a power of 2.  The cluster-size can only be
              specified if the bigalloc feature is enabled.  (See the
              ext4(5) man page for more details about bigalloc.)   The
              default cluster size if bigalloc is enabled is 16 times
              the block size.

       -d root-directory|tarball
              Copy the contents of the given directory or tarball into
              the root directory of the file system. Tarball input is
              only available if mke2fs was compiled with libarchive
              support enabled and if the libarchive shared library is
              available at run-time. The special value "-" will read a
              tarball from standard input.

       -D     Use direct I/O when writing to the disk.  This avoids
              mke2fs dirtying a lot of buffer cache memory, which may
              impact other applications running on a busy server.  This
              option will cause mke2fs to run much more slowly, however,
              so there is a tradeoff to using direct I/O.

       -e error-behavior
              Change the behavior of the kernel code when errors are
              detected.  In all cases, a file system error will cause
              e2fsck(8) to check the file system on the next boot.
              error-behavior can be one of the following:

                          Continue normal execution.

                          Remount file system read-only.

                   panic  Cause a kernel panic.

       -E extended-options
              Set extended options for the file system.  Extended
              options are comma separated, and may take an argument
              using the equals ('=') sign.  The -E option used to be -R
              in earlier versions of mke2fs.  The -R option is still
              accepted for backwards compatibility, but is deprecated.
              The following extended options are supported:

                          Enable the casefold feature in the super block
                          and set encoding-name as the encoding to be
                          used.  If encoding-name is not specified, the
                          encoding defined in mke2fs.conf(5) is used.

                          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.  To
                          disable a flag, add it to the list with the
                          prefix "no".

                          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

                          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 file system for a RAID array
                          with stride-size file system blocks. This is
                          the number of blocks read or written to disk
                          before moving to the next disk, which is
                          sometimes referred to as the chunk size.  This
                          mostly affects placement of file system
                          metadata like bitmaps at mke2fs time to avoid
                          placing them on a single disk, which can hurt
                          performance.  It may also be used by the block

                          Configure the file system for a RAID array
                          with stripe-width file system blocks per
                          stripe. This is typically stride-size * N,
                          where N is the number of data-bearing disks in
                          the RAID (e.g. for RAID 5 there is one parity
                          disk, so N will be the number of disks in the
                          array minus 1).  This allows the block
                          allocator to prevent read-modify-write of the
                          parity in a RAID stripe if possible when the
                          data is written.

                          Create the file system at an offset from the
                          beginning of the device or file.  This can be
                          useful when creating disk images for virtual

                          Reserve enough space so that the block group
                          descriptor table can grow to support a file
                          system that has max-online-resize blocks.

                   lazy_itable_init[= <0 to disable, 1 to enable>]
                          If enabled and the uninit_bg feature is
                          enabled, the inode table will not be fully
                          initialized by mke2fs.  This speeds up file
                          system initialization noticeably, but it
                          requires the kernel to finish initializing the
                          file system in the background when the file
                          system is first mounted.  If the option value
                          is omitted, it defaults to 1 to enable lazy
                          inode table zeroing.

                   lazy_journal_init[= <0 to disable, 1 to enable>]
                          If enabled, the journal inode will not be
                          fully zeroed out by mke2fs.  This speeds up
                          file system initialization noticeably, but
                          carries some small risk if the system crashes
                          before the journal has been overwritten
                          entirely one time.  If the option value is
                          omitted, it defaults to 1 to enable lazy
                          journal inode zeroing.

                   assume_storage_prezeroed[= <0 to disable, 1 to
                          If enabled, mke2fs assumes that the storage
                          device has been prezeroed, skips zeroing the
                          journal and inode tables, and annotates the
                          block group flags to signal that the inode
                          table has been zeroed.

                          Normally mke2fs will copy the extended
                          attributes of the files in the directory
                          hierarchy specified via the (optional) -d
                          option.  This will disable the copy and leaves
                          the files in the newly created file system
                          without any extended attributes.

                          If the sparse_super2 file system feature is
                          enabled this option controls whether there
                          will be 0, 1, or 2 backup superblocks created
                          in the file system.

                   packed_meta_blocks[= <0 to disable, 1 to enable>]
                          Place the allocation bitmaps and the inode
                          table at the beginning of the disk.  This
                          option requires that the flex_bg file system
                          feature to be enabled in order for it to have
                          effect, and will also create the journal at
                          the beginning of the file system.  This option
                          is useful for flash devices that use SLC flash
                          at the beginning of the disk.  It also
                          maximizes the range of contiguous data blocks,
                          which can be useful for certain specialized
                          use cases, such as supported Shingled Drives.

                          Specify the numeric user and group ID of the
                          root directory.  If no UID:GID is specified,
                          use the user and group ID of the user running
                          mke2fs.  In mke2fs 1.42 and earlier the UID
                          and GID of the root directory were set by
                          default to the UID and GID of the user running
                          the mke2fs command.  The root_owner= option
                          allows explicitly specifying these values, and
                          avoid side-effects for users that do not
                          expect the contents of the file system to
                          change based on the user running mke2fs.

                          Specify the root directory permissions in
                          octal format. If no permissions are specified
                          then the root directory permissions would be
                          set in accordance with the default filesystem

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

                          Set size of the file for tracking unlinked but
                          still open inodes and inodes with truncate in
                          progress. Larger file allows for better
                          scalability, reserving a few blocks per cpu is

                          Attempt to discard blocks at mkfs time
                          (discarding blocks initially is useful on
                          solid state devices and sparse / thin-
                          provisioned storage). When the device
                          advertises that discard also zeroes data (any
                          subsequent read after the discard and before
                          write returns zero), then mark all not-yet-
                          zeroed inode tables as zeroed. This
                          significantly speeds up file system
                          initialization. This is set as default.

                          Do not attempt to discard blocks at mkfs time.

                          Specify the which  quota types (usrquota,
                          grpquota, prjquota) which should be enabled in
                          the created file system.  The argument of this
                          extended option should be a colon separated
                          list.  This option has effect only if the
                          quota feature is set.   The default quota
                          types to be initialized if this option is not
                          specified is both user and group quotas.  If
                          the project feature is enabled that project
                          quotas will be initialized as well.

       -F     Force mke2fs to create a file system, even if the
              specified device is not a partition on a block special
              device, or if other parameters do not make sense.  In
              order to force mke2fs to create a file system even if the
              file system appears to be in use or is mounted (a truly
              dangerous thing to do), this option must be specified

       -g blocks-per-group
              Specify the number of blocks in a block group.  There is
              generally no reason for the user to ever set this
              parameter, as the default is optimal for the file system.
              (For administrators who are creating file systems on RAID
              arrays, it is preferable to use the stride RAID parameter
              as part of the -E option rather than manipulating the
              number of blocks per group.)  This option is generally
              used by developers who are developing test cases.

              If the bigalloc feature is enabled, the -g option will
              specify the number of clusters in a block group.

       -G number-of-groups
              Specify the number of block groups that will be packed
              together to create a larger virtual block group (or
              "flex_bg group") in an ext4 file system.  This improves
              meta-data locality and performance on meta-data heavy
              workloads.  The number of groups must be a power of 2 and
              may only be specified if the flex_bg file system feature
              is enabled.

       -i bytes-per-inode
              Specify the bytes/inode ratio.  mke2fs creates an inode
              for every bytes-per-inode bytes of space on the disk.  The
              larger the bytes-per-inode ratio, the fewer inodes will be
              created.  This value generally shouldn't be smaller than
              the blocksize of the file system, since in that case more
              inodes would be made than can ever be used.  Be warned
              that it is not possible to change this ratio on a file
              system after it is created, so be careful deciding the
              correct value for this parameter.  Note that resizing a
              file system changes the number of inodes to maintain this

       -I inode-size
              Specify the size of each inode in bytes.  The inode-size
              value must be a power of 2 larger or equal to 128.  The
              larger the inode-size the more space the inode table will
              consume, and this reduces the usable space in the file
              system and can also negatively impact performance.  It is
              not possible to change this value after the file system is

              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.

              The default inode size is controlled by the mke2fs.conf(5)
              file.  In the mke2fs.conf file shipped with e2fsprogs, the
              default inode size is 256 bytes for all file systems,
              except for the GNU Hurd since it only supports 128-byte

       -j     Create the file system with an ext3 journal.  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 file system) stored within the file
              system.  Note that you must be using a kernel which has
              ext3 support in order to actually make use of the journal.

       -J journal-options
              Create the ext3 journal using options specified on the
              command-line.  Journal options are comma separated, and
              may take an argument using the equals ('=')  sign.  The
              following journal options are supported:

                          Create an internal journal (i.e., stored
                          inside the file system) of size journal-size
                          megabytes.  The size of the journal must be at
                          least 1024 file system blocks (i.e., 1MB if
                          using 1k blocks, 4MB if using 4k blocks, etc.)
                          and may be no more than 10,240,000 file system
                          blocks or half the total file system size
                          (whichever is smaller)

                          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 file system 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 file system to the journal block
                          device located on external-journal.  The
                          external journal must already have been
                          created using the command

                          mke2fs -O journal_dev external-journal

                          Note that external-journal must have been
                          created with the same block size as the new
                          file system.  In addition, while there is
                          support for attaching multiple file systems 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
              file system.

       -l filename
              Read the bad blocks list from filename.  Note that the
              block numbers in the bad block list must be generated
              using the same block size as used by mke2fs.  As a result,
              the -c option to mke2fs is a much simpler and less error-
              prone method of checking a disk for bad blocks before
              formatting it, as mke2fs will automatically pass the
              correct parameters to the badblocks program.

       -L new-volume-label
              Set the volume label for the file system to new-volume-
              label.  The maximum length of the volume label is 16

       -m reserved-blocks-percentage
              Specify the percentage of the file system blocks reserved
              for the super-user.  This avoids fragmentation, and allows
              root-owned daemons, such as syslogd(8), to continue to
              function correctly after non-privileged processes are
              prevented from writing to the file system.  The default
              percentage is 5%.

       -M last-mounted-directory
              Set the last mounted directory for the file system.  This
              might be useful for the sake of utilities that key off of
              the last mounted directory to determine where the file
              system should be mounted.

       -n     Causes mke2fs to not actually create a file system, but
              display what it would do if it were to create a file
              system.  This can be used to determine the location of the
              backup superblocks for a particular file system, so long
              as the mke2fs parameters that were passed when the file
              system was originally created are used again.  (With the
              -n option added, of course!)

       -N number-of-inodes
              Overrides the default calculation of the number of inodes
              that should be reserved for the file system (which is
              based on the number of blocks and the bytes-per-inode
              ratio).  This allows the user to specify the number of
              desired inodes directly.

       -o creator-os
              Overrides the default value of the "creator operating
              system" field of the file system.  The creator field is
              set by default to the name of the OS the mke2fs executable
              was compiled for.

       -O [^]feature[,...]
              Create a file system with the given features (file system
              options), overriding the default file system options.  The
              features that are enabled by default are specified by the
              base_features relation, either in the [defaults] section
              in the /etc/mke2fs.conf configuration file, or in the
              [fs_types] subsections for the usage types as specified by
              the -T option, further modified by the features relation
              found in the [fs_types] subsections for the file system
              and usage types.  See the mke2fs.conf(5) manual page for
              more details.  The file system type-specific configuration
              setting found in the [fs_types] section will override the
              global default found in [defaults].

              The file system feature set will be further edited using
              either the feature set specified by this option, or if
              this option is not given, by the default_features relation
              for the file system type being created, or in the
              [defaults] section of the configuration file.

              The file system feature set is comprised of a list of
              features, separated by commas, that are to be enabled.  To
              disable a feature, simply prefix the feature name with a
              caret ('^') character.  Features with dependencies will
              not be removed successfully.  The pseudo-file system
              feature "none" will clear all file system features.

       For more information about the features which can be set, please
              the manual page ext4(5).

       -q     Quiet execution.  Useful if mke2fs is run in a script.

       -r revision
              Set the file system revision for the new file system.
              Note that 1.2 kernels only support revision 0 file
              systems.  The default is to create revision 1 file

       -S     Write superblock and group descriptors only.  This is an
              extreme measure to be taken only in the very unlikely case
              that all of the superblock and backup superblocks are
              corrupted, and a last-ditch recovery method is desired by
              experienced users.  It causes mke2fs to reinitialize the
              superblock and group descriptors, while not touching the
              inode table and the block and inode bitmaps.  The e2fsck
              program should be run immediately after this option is
              used, and there is no guarantee that any data will be
              salvageable.  Due to the wide variety of possible options
              to mke2fs that affect the on-disk layout, it is critical
              to specify exactly the same format options, such as
              blocksize, fs-type, feature flags, and other tunables when
              using this option, or the file system will be further
              corrupted.  In some cases, such as file systems that have
              been resized, or have had features enabled after format
              time, it is impossible to overwrite all of the superblocks
              correctly, and at least some file system corruption will
              occur.  It is best to run this on a full copy of the file
              system so other options can be tried if this doesn't work.

       -t fs-type
              Specify the file system type (i.e., ext2, ext3, ext4,
              etc.) that is to be created.  If this option is not
              specified, mke2fs will pick a default either via how the
              command was run (for example, using a name of the form
              mkfs.ext2, mkfs.ext3, etc.) or via a default as defined by
              the /etc/mke2fs.conf file.   This option controls which
              file system options are used by default, based on the
              fstypes configuration stanza in /etc/mke2fs.conf.

              If the -O option is used to explicitly add or remove file
              system options that should be set in the newly created
              file system, the resulting file system may not be
              supported by the requested fs-type.  (e.g., "mke2fs -t
              ext3 -O extent /dev/sdXX" will create a file system that
              is not supported by the ext3 implementation as found in
              the Linux kernel; and "mke2fs -t ext3 -O ^has_journal
              /dev/hdXX" will create a file system that does not have a
              journal and hence will not be supported by the ext3 file
              system code in the Linux kernel.)

       -T usage-type[,...]
              Specify how the file system is going to be used, so that
              mke2fs can choose optimal file system parameters for that
              use.  The usage types that are supported are defined in
              the configuration file /etc/mke2fs.conf.  The user may
              specify one or more usage types using a comma separated

              If this option is is not specified, mke2fs will pick a
              single default usage type based on the size of the file
              system to be created.  If the file system size is less
              than 3 megabytes, mke2fs will use the file system type
              floppy.  If the file system size is greater than or equal
              to 3 but less than 512 megabytes, mke2fs(8) will use the
              file system type small.  If the file system size is
              greater than or equal to 4 terabytes but less than 16
              terabytes, mke2fs(8) will use the file system type big.
              If the file system size is greater than or equal to 16
              terabytes, mke2fs(8) will use the file system type huge.
              Otherwise, mke2fs(8) will use the default file system type

       -U UUID
              Set the universally unique identifier (UUID) of the file
              system 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 file system UUID

                   random generate a new randomly-generated UUID

                   time   generate a new time-based UUID

       -v     Verbose execution.

       -V     Print the version number of mke2fs and exit.

       -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 mke2fs-device.e2undo in
              the directory specified via the E2FSPROGS_UNDO_DIR
              environment variable or the undo_dir directive in the
              configuration file.

              WARNING: The undo file cannot be used to recover from a
              power or system crash.

ENVIRONMENT         top

              If set to non-zero integer value, its value is used to
              determine how often sync(2) is called during inode table

              Determines the location of the configuration file (see

              If set to non-zero integer value, its value is used to
              determine first meta block group. This is mostly for
              debugging purposes.

              If set to non-zero integer value, its value is used to
              determine logical sector size of the device.

              If set to non-zero integer value, its value is used to
              determine physical sector size of the device.

              If set, do not show the message of file system automatic
              check caused by mount count or check interval.

AUTHOR         top

       This version of mke2fs has been written by Theodore Ts'o

AVAILABILITY         top

       mke2fs is part of the e2fsprogs package and is available from

SEE ALSO         top

       mke2fs.conf(5), badblocks(8), dumpe2fs(8), e2fsck(8), tune2fs(8),

COLOPHON         top

       This page is part of the e2fsprogs (utilities for ext2/3/4
       filesystems) project.  Information about the project can be found
       at ⟨⟩.  It is not known how to
       report bugs for this man page; if you know, please send a mail to  This page was obtained from the project's
       upstream Git repository
       ⟨git://⟩ on
       2024-06-14.  (At that time, the date of the most recent commit
       that was found in the repository was 2024-05-20.)  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

E2fsprogs version 1.47.1        May 2024                       MKE2FS(8)

Pages that refer to this page: crypttab(5)ext4(5)mke2fs.conf(5)badblocks(8)debugfs(8)dumpe2fs(8)e2fsck(8)e2label(8)e2undo(8)e4crypt(8)e4defrag(8)mke2fs(8)mkfs(8)mklost+found(8)mount(8)resize2fs(8)tune2fs(8)