mkfs.ext4(8)
NAME
mke2fs - create an ext2/ext3/ext4 filesystem
SYNOPSIS
mke2fs [ -c | -l filename ] [ -b block-size ] [ -d root-directory ] [ -D ] [ -f fragment-size ] [ -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 filesystem, 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 filesystem, if not overridden by the options listed below, are controlled by the /etc/mke2fs.conf configuration file. See the mke2fs.conf(5) manual page for more details.
OPTIONS
-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 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 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 block size.
-d root-directory
Copy the contents of the given directory into the root directory
of the filesystem.
-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 filesystem error will cause e2fsck(8) to check
the filesystem on the next boot. error-behavior can be one of
the following:
continue Continue normal execution.
remount-ro Remount filesystem read-only.
panic 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 supported:
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 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.
stripe_width=stripe-width
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 is
written.
offset=offset
Create the filesystem at an offset from the
beginning 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
descriptor table can grow to support a filesystem
that has max-online-resize blocks.
lazy_itable_init[= <0 to disable, 1 to enable>]
If enabled and the uninit_bg feature is enabled, the
inode table will not be fully initialized by mke2fs.
This speeds up filesystem initialization noticeably,
but it requires the kernel to finish initializing
the filesystem in the background when the filesystem
is first mounted. If the option value is omitted,
it defaults to 1 to enable lazy inode table 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 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.
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
maximizes 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
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 running mke2fs.
test_fs
Set a flag in the filesystem superblock indicating
that it may be mounted using experimental kernel
code, such as the ext4dev filesystem.
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
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.
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
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.
-f fragment-size
Specify the size of fragments in bytes.
-F Force mke2fs to create a filesystem, even if the specified
device is not a partition on a block special device, or if other
parameters do not make sense. In order to force mke2fs to
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.
-j Create the filesystem with an ext3 journal. If the -J option is
not specified, the default journal parameters will be used to
create an appropriately sized journal (given the size of the
filesystem) stored within the filesystem. Note that you must be
using a kernel which has ext3 support in order to actually make
use of the journal.
-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:
size=journal-size
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)
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 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
tune2fs(8).
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
program.
-L new-volume-label
Set the volume label for the filesystem to new-volume-label.
The maximum length of the volume label is 16 bytes.
-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.
-n Causes mke2fs to not actually create a filesystem, but display
what it would do if it were to create a filesystem. This can be
used to determine the location of the backup superblocks for a
particular filesystem, so long as the mke2fs parameters that
were passed when the filesystem was originally created are used
again. (With the -n option added, of course!)
-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 [defaults].
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, please see
the manual page ext4(5).
-q Quiet execution. Useful if mke2fs is run in a script.
-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.
-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
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 work.
-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 kernel.)
-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 type default.
-U UUID
Create the filesystem with the specified 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
physical sector size of the device.
MKE2FS_SKIP_CHECK_MSG
If set, do not show the message of filesystem automatic check
caused by mount count or check interval.
AUTHOR
This version of mke2fs has been written by Theodore Ts'o <tytso@mit.edu>.
BUGS
mke2fs accepts the -f option but currently ignores it because the second extended file system does not support fragments yet. There may be other ones. Please, report them to the author.
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)
Opportunity
Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.
Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.
Free Software
Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.
Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.
Free Books
The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.
Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.
Education
Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.
Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.
