mke2fs [ -c | -l filename ] [ -b block-size ] [ -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 fea-
ture[,...] ] [ -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 ]
mke2fs is used to create an ext2, ext3, or ext4 filesystem, usually in
a disk partition. device is the special 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
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.
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.
-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.
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 compati-
bility. The following extended options are supported:
Adjust the initial MMP update interval to interval
seconds. Specifying an interval of 0 means to use
the default interval. The specified interval must
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 writ-
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 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 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.
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.
parameters do not make sense. In order to force mke2fs to cre-
ate a filesystem even if the filesystem appears to be in use or
is mounted (a truly dangerous thing to do), this option must be
Specify the number of blocks in a block group. There is gener-
ally 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 test cases.
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 per-
formance 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.
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
expand the number of inodes on a filesystem after it is created,
so be careful deciding the correct value for this parameter.
Specify the size of each inode in bytes. mke2fs creates
256-byte inodes by default. 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 perfor-
mance. 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.
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. It is not possible to change this value
after the filesystem is created.
-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.
(whichever is smaller)
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 mul-
tiple 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, exter-
nal-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
Only one of the size or device options can be given for a
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 auto-
matically pass the correct parameters to the badblocks program.
Set the volume label for the filesystem to new-volume-label.
The maximum length of the volume label is 16 bytes.
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%.
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
-n Causes mke2fs to not actually create a filesystem, but display
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.
Create a filesystem with the given features (filesystem
options), overriding the default filesystem options. The fea-
tures that are enabled by default are specified by the base_fea-
tures relation, either in the [defaults] section in the
/etc/mke2fs.conf configuration file, or in the [fs_types] sub-
sections for the usage types as specified by the -T option, fur-
ther 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] sec-
tion 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 configu-
The filesystem feature set is comprised of a list of features,
separated by commas, that are to be enabled. To disable a fea-
ture, simply prefix the feature name with a caret ('^') charac-
ter. The pseudo-filesystem feature "none" will clear all
Use hashed b-trees to speed up lookups in large
extent Instead of using the indirect block scheme for stor-
ing the location of data blocks in an inode, use
extents instead. This is a much more efficient
encoding which speeds up filesystem access, espe-
cially for large files.
Store file type information in directory entries.
Allow the per-block group metadata (allocation bit-
maps and inode tables) to be placed anywhere on the
storage media. In addition, mke2fs will place the
per-block group metadata together starting at the
first block group of each "flex_bg group". The
size of the flex_bg group can be specified using the
Create an ext3 journal (as if using the -j option).
quota Create quota inodes (inode# 3 for userquota and
inode# 4 for group quota) and set them in the
superblock. With this feature, the quotas will be
enabled automatically when the filesystem is
Reserve space so the block group descriptor table
may grow in the future. Useful for online resizing
using resize2fs. By default mke2fs will attempt to
reserve enough space so that the filesystem may grow
to 1024 times its initial size. This can be changed
using the resize extended option.
Create a filesystem with fewer superblock backup
copies (saves space on large filesystems).
Create a filesystem without initializing all of the
block groups. This feature also enables checksums
and highest-inode-used statistics in each block-
group. This feature can speed up filesystem cre-
ation time noticeably (if lazy_itable_init is
enabled), and can also reduce e2fsck time dramati-
cally. It is only supported by the ext4 filesystem
in recent Linux kernels.
-q Quiet execution. Useful if mke2fs is run in a script.
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
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 salvage-
able. It is critical to specify the correct filesystem block-
size when using this option, or there is no chance of recovery.
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(5) file. This
option controls which filesystem options are used by default,
based on the fstypes configuration stanza in
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(5). 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.
Create the filesystem with the specified UUID.
-v Verbose execution.
-V Print the version number of mke2fs and exit.
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
mke2fs accepts the -f option but currently ignores it because the sec-
ond extended file system does not support fragments yet.
There may be other ones. Please, report them to the author.
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