Manual: mkfs.ext2
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|tarball ] [ -D ] [ -g blocks-
per-group ] [ -G number-of-groups ] [ -i bytes-per-inode ] [ -I inode-size ] [ -j ] [ -J journal-options ] [ -N numā
ber-of-inodes ] [ -n ] [ -m reserved-blocks-percentage ] [ -o creator-os ] [ -O [^]feature[,...] ] [ -q ] [ -E exā
tended-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 blockā
size blocks. If the fs-size is suffixed by 'k', 'm', 'g', 't' (either upper-case or lower-case), then it is interā
preted 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.
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
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 usā
ing 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 zeā
roed.
discard
Attempt to discard blocks at mkfs time (discarding blocks initially is useful on solid state deā
vices 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 reā
jected 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 finā
ish 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 enā
able 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 speciā
fied 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 reā
quires 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 deā
vices 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 creā
ated 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 alā
lows 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 kerā
nel 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 deā
vice, 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 paā
rameter, 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 manipulatā
ing 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 parameā
ters 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 jourā
nal, 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 LAā
BEL=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 offā
set 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 opā
tions. 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] subsecā
tions 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 suā
perblocks 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 inā
ode bitmaps. The e2fsck program should be run immediately after this option is used, and there is no guaranā
tee 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 imā
possible 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 conā
trols 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 creā
ated 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-deā
vice.e2undo in the directory specified via the E2FSPROGS_UNDO_DIR environment variable or the undo_dir direcā
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 taā
ble 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 .
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 1.47.2 January 2025 MKE2FS(8)