mke2fs - create an ext2/ext3/ext4 file system
mke2fs [ -c | -l filename ] [
-b block-size ] [ -C cluster-size ] [ -d
root-directory ] [ -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 ]
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.
- -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.
- 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 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
- 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.
- 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
- 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
- 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
- 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
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 disabled.
- 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 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.
<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.
<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.
<0 to disable, 1 to enable>]
- 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.
<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.
- 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 ideal.
- 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
- 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 twice.
- 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
- If the bigalloc feature is enabled, the -g option will specify the
number of clusters in a block group.
- 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.
- 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 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 file system and can also negatively impact performance. It is
not possible to change this value after the file system is created.
- 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 most file systems, except for small file systems where
the inode size will be 128 bytes.
- 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.
- 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 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 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
- 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.
- Set the volume label for the file system to new-volume-label. The
maximum length of the volume label is 16 bytes.
- 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%.
- 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.
- 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!)
- 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.
- 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
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
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
- 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 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 systems.
- 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.)
- 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 list.
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 default.
- -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 the file system UUID
- generate a new randomly-generated UUID
- generate a new time-based 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 crash.
- 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 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.
This version of mke2fs has been written by Theodore Ts'o
mke2fs is part of the e2fsprogs package and is available
mke2fs.conf(5), badblocks(8), dumpe2fs(8),
e2fsck(8), tune2fs(8), ext4(5)