mke2fs - create an ext2/ext3/ext4 filesystem
| -l filename
] [ -b
] [ -d root-directory
] [ -D
] [ -G number-of-groups
] [ -I inode-size
] [ -j
] [ -J journal-options
] [ -N number-of-inodes
] [ -m reserved-blocks-percentage
] [ -o
] [ -O
[,...] ] [ -q
] [ -E extended-options
] [ -F
] [ -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
- 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
- -d root-directory
- Copy the contents of the given directory into the root
directory of the filesystem.
- 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
- 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 allocator.
- 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
- Create the filesystem at an offset from the beginning of
the device or file. This can be useful when creating disk images for
- Reserve enough space so that the block group descriptor
table can grow to support a filesystem that has max-online-resize
- 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
- Set a flag in the filesystem superblock indicating that it
may be mounted using experimental kernel code, such as the ext4dev
- 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 well.
- 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 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 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 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 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
- -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
- 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 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
- Only one of the size or device options can be
given for a filesystem.
- -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
- -L new-volume-label
- Set the volume label for the filesystem to
new-volume-label. The maximum length of the volume label is 16
- -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,
- the manual page ext4(5).
- Quiet execution. Useful if mke2fs is run in a
- -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 filesystems.
- 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
- -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
- Set the universally unique identifier (UUID) of the
filesystem 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 filesystem 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
- If set to non-zero integer value, its value is used to
determine how often sync(2) is called during inode table
- 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
- 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
is part of the e2fsprogs package and is available from