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 ] [ -K ] [ -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 negative, 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 cer-
tain hardware devices which require that the blocksize be a mul-
tiple 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:
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
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 initial-
Set a flag in the filesystem superblock indicating
that it may be mounted using experimental kernel
code, such as the ext4dev filesystem.
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 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.
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.
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 102,400
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
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
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!)
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.
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
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).
Create an external ext3 journal on the given device
instead of a regular ext2 filesystem. Note that
external-journal must be created with the same block
size as the filesystems that will be using it.
Filesystem can contain files that are greater than
2GB. (Modern kernels set this feature automatically
when a file > 2GB is created.)
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
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
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 extents /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 kernel.)
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 small. 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.
This version of mke2fs has been written by Theodore Ts'o
E2fsprogs version 1.41.11 March 2010 MKE2FS(8)
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