mke2fs - create an ext2/ext3/ext4 filesystem
| -l filename
] [ -b
] [ -d root-directory
] [ -D
] [ -g blocks-per-group
] [ -i bytes-per-inode
] [ -j
] [ -J journal-options
] [ -N number-of-inodes
] [ -n
] [ -m
] [ -o creator-os
[,...] ] [ -q
] [ -r
] [ -E extended-options
] [ -v
] [ -L volume-label
] [ -M
] [ -S
] [ -t fs-type
] [ -U UUID
] [ -V
] [ -z undo_file
mke2fs -O journal_dev
[ -b block-size
] [ -L
] [ -n
] [ -q
] [ -v
is used to create an ext2, ext3, or ext4 filesystem, usually in a
disk partition (or file) named by device
The file system size is specified by fs-size
. If fs-size
have a suffix, it is interpreted as power-of-two kilobytes, unless the
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.
is omitted, mke2fs
will create the file system based
on the device size.
is run as mkfs.XXX
, or mkfs.ext4
) the option -t XXX
implied; so mkfs.ext3
will create a file system for use with ext3,
will create a file system for use with ext4, and so on.
The defaults of the parameters for the newly created filesystem, if not
overridden by the options listed below, are controlled by the
configuration file. See the mke2fs.conf(5)
manual page for more details.
- -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 blocksize be a multiple of 2k.
- 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
- -d root-directory
- Copy the contents of the given directory into the root directory of the
- 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 filesystem error will cause e2fsck(8) to check the
filesystem on the next boot. error-behavior can be one of the
- Continue normal execution.
- Remount filesystem read-only.
- 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
-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
- 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 the next disk, which is sometimes referred to as the
chunk size. This mostly affects placement of filesystem 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 filesystem for a RAID array with stripe-width
filesystem 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 filesystem 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 filesystem that has max-online-resize blocks.
- lazy_itable_init[= <0 to disable, 1 to
- If enabled and the uninit_bg feature is enabled, the inode table will not
be fully initialized 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 zeroing.
- lazy_journal_init[= <0 to disable, 1 to
- 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.
- 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
- 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 filesystem to change based on the user running mke2fs.
- Set a flag in the filesystem superblock indicating that it may be mounted
using experimental kernel code, such as the ext4dev filesystem.
- 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
filesystem 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
- -f fragment-size
- Specify the size of fragments in bytes.
- 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 who are developing
- 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
filesystem. 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 filesystem 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 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 filesystem changes the numer 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 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.
- 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 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 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 or half
the total file system size (whichever is smaller)
- 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 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
- 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 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 filesystem to new-volume-label. The
maximum length of the volume label is 16 bytes.
- -m reserved-blocks-percentage
- Specify the percentage of the filesystem 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 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.
- 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 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 filesystem (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 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
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 ('^') 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).
- 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
- 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 filesystem will
be further corrupted. In some cases, such as filesystems 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
filesystem corruption will occur. It is best to run this on a full copy of
the filesystem so other options can be tried if this doesn't work.
- -t fs-type
- Specify the filesystem 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 filesystem
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 filesystem
options that should be set in the newly created filesystem, the resulting
filesystem may not be supported by the requested fs-type. (e.g.,
" mke2fs -t ext3 -O extent /dev/sdXX" will create a
filesystem 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 filesystem that does not have a journal
and hence will not be supported by the ext3 filesystem code in the Linux
- -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 3 megabytes, mke2fs will use the
filesystem type floppy. If the filesystem size is greater than or
equal to 3 but less than 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
- -U UUID
- Create the filesystem with the specified UUID.
- Verbose execution.
- 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
- If set to non-zero integer value, its value is used to determine how often
sync(2) is called during inode table initialization.
- 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 physical
sector size of the device.
- If set, do not show the message of filesystem automatic check caused by
mount count or check interval.
This version of mke2fs
has been written by Theodore Ts'o
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.
is part of the e2fsprogs package and is available from