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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | ENVIRONMENT | AUTHOR | AVAILABILITY | SEE ALSO | COLOPHON |
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MKE2FS(8) System Manager's Manual MKE2FS(8)
mke2fs - create an ext2/ext3/ext4 file system
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 ] [ -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.
-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
Continue normal execution.
remount-ro
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:
assume_storage_prezeroed[= <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.
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
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.
encoding=encoding-name
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.
encoding_flags=encoding-flags
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 disabled.
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.
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. nodiscard Do not attempt to discard
blocks at mkfs time.
no_copy_xattrs
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.
num_backup_sb=<0|1|2>
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.
offset=offset
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
machines.
orphan_file_size=size
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.
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.
quotatype
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.
resize=max-online-resize
Reserve enough space so that the block group
descriptor table can grow to support a file
system that has max-online-resize blocks.
revision=fs-revision
Specify the file system revision number.
Revision 0 file systems provide compatibility
with pre-1.2 Linux kernels (dating from before
1995). This is only needed for testing or
people who want to use very early, historical
Linux systems. The current default (supported
by all modern Linux systems) is revision 1.
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 file system to change based on
the user running mke2fs.
root_perms[=permissions]
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 umask.
stride=stride-size
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 allocator.
stripe_width=stripe-width
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.
test_fs
Set a flag in the file system superblock
indicating that it may be mounted using
experimental kernel code, such as the ext4dev
file system.
-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 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 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 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 all file systems,
except for the GNU Hurd since it only supports 128-byte
inodes.
-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:
device=external-journal
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).
fast_commit_size=fast-commit-size
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).
location=journal-location
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.
size=journal-size
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)
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 bytes.
-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 see the manual page ext4(5).
-q Quiet execution. Useful if mke2fs is run in a script. -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 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 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.
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 logical sector size of the device.
MKE2FS_DEVICE_PHYS_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 file system automatic
check caused by mount count or check interval.
This version of mke2fs has been written by Theodore Ts'o
<[email protected]>.
mke2fs is part of the e2fsprogs package and is available from
http://e2fsprogs.sourceforge.net.
mke2fs.conf(5), badblocks(8), dumpe2fs(8), e2fsck(8), tune2fs(8),
ext4(5)
This page is part of the e2fsprogs (utilities for ext2/3/4
filesystems) project. Information about the project can be found
at ⟨http://e2fsprogs.sourceforge.net/⟩. It is not known how to
report bugs for this man page; if you know, please send a mail to
[email protected]. This page was obtained from the project's
upstream Git repository
⟨git://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git⟩ on
2025-08-11. (At that time, the date of the most recent commit
that was found in the repository was 2025-07-31.) 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 [email protected]
E2fsprogs version 1.47.3 July 2025 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)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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