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



NAME
       mke2fs - create an ext2/ext3/ext4 filesystem

SYNOPSIS
       mke2fs [ -c | -l filename ] [ -b block-size ] [ -D ] [ -f fragment-size ] [ -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 ] device [ blocks-count ]

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

DESCRIPTION
       mke2fs is used to create an ext2, ext3, or ext4 filesystem, usually in a disk partition.  device is  the  spe‐
       cial  file  corresponding  to the device (e.g /dev/hdXX).  blocks-count is the number of blocks on the device.
       If omitted, mke2fs automagically figures the file system size.  If called as mkfs.ext3 a journal is created as
       if the -j option was specified.

       The  defaults  of  the  parameters  for  the newly created filesystem, 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
       -b block-size
              Specify  the size of blocks in bytes.  Valid block-size values are 1024, 2048 and 4096 bytes per block.
              If omitted, block-size is heuristically determined by the filesystem size and the expected usage of the
              filesystem  (see  the -T option).  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 block‐
              size 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 filesystems using the bigalloc feature.  Valid cluster-size
              values are from 2048 to 256M bytes per cluster.  This 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     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 extended-options
              Set extended options for the filesystem.  Extended options are comma separated, and may take  an  argu‐
              ment  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:

                   mmp_update_interval=interval
                          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.

                          RAID stripe if possible when the data is written.

                   resize=max-online-resize
                          Reserve  enough  space  so  that  the  block  group  descriptor table can grow to support a
                          filesystem 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 initial‐
                          ized  by  mke2fs.  This speeds up filesystem initialization noticeably, but it requires the
                          kernel to finish initializing the filesystem in the background when the filesystem is first
                          mounted.  If the option value is omitted, it defaults to 1 to enable lazy inode table zero‐
                          ing.

                   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
                          filesystem  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.

                   root_owner[=uid:gid]
                          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 filesystem to change
                          based on the user running mke2fs.

                   test_fs
                          Set a flag in the filesystem superblock indicating that it may be mounted using  experimen‐
                          tal kernel code, such as the ext4dev filesystem.

                   discard
                          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  dis‐
                          card  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
                          filesystem initialization. This is set as default.

                   nodiscard
                          Do not attempt to discard blocks at mkfs time.

       -f fragment-size
              Specify the size of fragments in bytes.

       -F     Force mke2fs to create a filesystem, 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 filesystem even
              if  the filesystem appears to be in use or is mounted (a truly dangerous thing to do), this option must
              be specified twice.

       -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 filesystem.  (For administrators who are creating
              filesystems 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
              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 filesystem, 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 filesystem after it
              is created, so be careful deciding the correct value for this parameter.  Note that resizing a filesys‐
              tem changes the numer of inodes to maintain this ratio.

       -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 filesystem and can also negatively impact  performance.   It  is  not  possible  to
              change this value after the filesystem is created.

              In  kernels  after  2.6.10 and some earlier vendor kernels it is possible to utilize inodes larger than
              128 bytes to store extended attributes for improved performance.  Extended attributes stored  in  large
              inodes  are not visible with older kernels, and such filesystems will not be mountable with 2.4 kernels
              at all.

              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 most file systems, except for small file systems
              where the inode size will be 128 bytes.

       -j     Create the filesystem 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 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.

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

                   size=journal-size
                          Create  an  internal  journal  (i.e.,  stored  inside  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 filesys‐
                          tem blocks or half the total file system size (whichever is smaller)

                   device=external-journal
                          Attach the filesystem to the journal block device located on external-journal.  The  exter‐
                          nal 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
                          filesystem.  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 dis‐
                          play a journal device's volume label and UUID.  See also the -L option of tune2fs(8).

              Only one of the size or device options can be given for a filesystem.
              Specify  the  percentage  of the filesystem blocks reserved for the super-user.  This avoids fragmenta‐
              tion, and allows root-owned daemons, such as syslogd(8), to continue to function correctly  after  non-
              privileged processes are prevented from writing to the filesystem.  The default percentage is 5%.

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

       -n     Causes mke2fs to not actually create a filesystem, but display what it would do if it were to create  a
              filesystem.   This  can  be  used  to determine the location of the backup superblocks for a particular
              filesystem, so long as the mke2fs parameters that were passed when the filesystem was  originally  cre‐
              ated 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 filesystem
              (which is based on the number of blocks and the bytes-per-inode ratio).  This allows the user to  spec‐
              ify the number of desired inodes directly.

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

       -O feature[,...]
              Create a filesystem with the given features (filesystem options),  overriding  the  default  filesystem
              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 filesystem and usage types.  See the mke2fs.conf(5) manual page  for
              more  details.  The filesystem type-specific configuration setting found in the [fs_types] section will
              override the global default found in [defaults].

              The filesystem 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 filesystem type being
              created, or in the [defaults] section of the configuration file.

              The filesystem 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 ('^') or a minus ('-')
              character.  Features with dependencies will not be removed successfully.  The pseudo-filesystem feature
              "none" will clear all filesystem features.

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

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

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

       -S     Write superblock and group descriptors only.  This is useful  if  all  of  the  superblock  and  backup
              superblocks are corrupted, and a last-ditch recovery method is desired.  It causes mke2fs to reinitial‐
              ize 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 guar‐
              antee that any data will be salvageable.  It is critical to specify the  correct  filesystem  blocksize
              mentation as found in the Linux kernel; and "mke2fs -t ext3 -O ^has_journal /dev/hdXX"  will  create  a
              filesystem  that does not have a journal and hence will not be supported by the ext3 filesystem code in
              the Linux kernel.)

       -T usage-type[,...]
              Specify how the filesystem is going to be used, so that mke2fs can choose optimal filesystem 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 list.

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

       -U UUID
              Create the filesystem with the specified UUID.

       -v     Verbose execution.

       -V     Print the version number of mke2fs and exit.

ENVIRONMENT
       MKE2FS_SYNC
              If set to non-zero integer value, its value is used to determine how often  sync(2)  is  called  during
              inode table initialization.

       MKE2FS_CONFIG
              Determines the location of the configuration file (see mke2fs.conf(5)).

       MKE2FS_FIRST_META_BG
              If set to non-zero integer value, its value is used to determine first meta block group. This is mostly
              for debugging purposes.

       MKE2FS_DEVICE_SECTSIZE
              If set to non-zero integer value, its value is used to determine physical sector size of the device.

       MKE2FS_SKIP_CHECK_MSG
              If set, do not show the message of filesystem automatic check caused by mount count or check interval.

AUTHOR
       This version of mke2fs has been written by Theodore Ts'o <[email protected]>.

BUGS
       mke2fs accepts the -f option but currently ignores it because the second extended file system does not support
       fragments yet.
       There may be other ones.  Please, report them to the author.

AVAILABILITY
       mke2fs is part of the e2fsprogs package and is available from http://e2fsprogs.sourceforge.net.

SEE ALSO