MKE2FS(8) System Manager's Manual MKE2FS(8)
NAME
mke2fs - create an ext2/ext3/ext4 file system
SYNOPSIS
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 ]
DESCRIPTION
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 de-
vice 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.
OPTIONS
-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 are from 2048 to
256M bytes per cluster. This can only be specified if the bi-
galloc 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
Copy the contents of the given directory into the root directory
of the file system.
-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 compati-
bility, but is deprecated. The following extended options are
supported:
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 pa-
rameter, its default value is used. encoding-flags
should be a comma-separated lists of flags to be en-
abled. 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.
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.
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 per-
formance. It may also be used by the block alloca-
tor.
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 writ-
ten.
offset=offset
Create the file system at an offset from the begin-
ning of the device or file. This can be useful when
creating disk images for virtual machines.
resize=max-online-resize
Reserve enough space so that the block group de-
scriptor table can grow to support a file system
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 file system initialization notice-
ably, but it requires the kernel to finish initial-
izing 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 ze-
roed out by mke2fs. This speeds up file system ini-
tialization 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.
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.
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.
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 maxi-
mizes the range of contiguous data blocks, which can
be useful for certain specialized use cases, such as
supported Shingled Drives.
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 direc-
tory 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.
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.
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.
discard
Attempt to discard blocks at mkfs time (discarding
blocks initially is useful on solid state devices
and sparse / thin-provisioned storage). When the de-
vice 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.
nodiscard
Do not attempt to discard blocks at mkfs time.
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 de-
fault 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.
-F Force mke2fs to create a file system, even if the specified de-
vice 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 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 gener-
ally 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 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
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 in-
ode-size the more space the inode table will consume, and this
reduces the usable space in the file system and can also nega-
tively 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 in-
ode size is 256 bytes for most file systems, except for small
file systems where the inode size will be 128 bytes.
-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 ar-
gument using the equals ('=') sign. The following journal op-
tions are supported:
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 sys-
tem blocks (i.e., 1MB if using 1k blocks, 4MB if us-
ing 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)
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.
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 mul-
tiple 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, exter-
nal-journal can also be specified by either LA-
BEL=label or UUID=UUID to locate the external jour-
nal 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 la-
bel and UUID. See also the -L option of tune2fs(8).
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 auto-
matically 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 cor-
rectly 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 op-
tions), overriding the default file system 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 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] sec-
tion 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 configu-
ration file.
The file system 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. Features with dependencies will not be removed success-
fully. 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.
-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.
-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 descrip-
tors, 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 op-
tions 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 op-
tion, 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 over-
write 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 jour-
nal 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 us-
age 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 sys-
tem 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 sepa-
rated 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 direc-
tive in the configuration file.
WARNING: The undo file cannot be used to recover from a power or
system crash.
ENVIRONMENT
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.
AUTHOR
This version of mke2fs has been written by Theodore Ts'o
<tytso@mit.edu>.
AVAILABILITY
mke2fs is part of the e2fsprogs package and is available from
http://e2fsprogs.sourceforge.net.
SEE ALSO
mke2fs.conf(5), badblocks(8), dumpe2fs(8), e2fsck(8), tune2fs(8),
ext4(5)
E2fsprogs version 1.47.0 February 2023 MKE2FS(8)
Generated by dwww version 1.16 on Tue Dec 16 11:11:49 CET 2025.