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 number-of-inodes ] [ -n ] [ -m reserved-blocks-percentage
] [ -o creator-os ] [ -O [^]feature[,...] ] [ -q ] [ -E extended-op-
tions ] [ -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 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 con-
straint 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 bi-
galloc.) 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 ap-
plications 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 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 in-
ode tables, and annotates the block group flags to
signal that the inode table has been zeroed.
discard
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 subse-
quent 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 ini-
tialization. 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 en-
coding-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.
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 finish 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 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.
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 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.
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.
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 requires that
the flex_bg file system feature to be enabled in or-
der 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.
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 default quota
types to be initialized if this option is not speci-
fied is both user and group quotas. If the project
feature is enabled that project quotas will be ini-
tialized as well.
resize=max-online-resize
Reserve enough space so that the block group descrip-
tor 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 di-
rectory. 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= op-
tion 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 for-
mat. 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 perfor-
mance. 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 allows the block alloca-
tor 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 kernel
code, such as the ext4dev file system.
-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 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 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 perfor-
mance 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 resiz-
ing 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 time-
stamps 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 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 us-
ing 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 argu-
ment 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 multi-
ple 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 LABEL=la-
bel 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 la-
bel 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 to-
tal 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.
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 num-
bers 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 op-
tions), overriding the default file system 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] subsec-
tions for the usage types as specified by the -T option, further
modified by the features relation found in the [fs_types] subsec-
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] 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. -S Write
superblock and group descriptors only. This is an extreme mea-
sure 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, fea-
ture 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 impossible to overwrite all of the su-
perblocks 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 de-
fault as defined by the /etc/mke2fs.conf file. This option con-
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 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 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 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 de-
fault usage type based on the size of the file system to be cre-
ated. 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 de-
fault 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 directive
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 1.47.2 January 2025 MKE2FS(8)
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