MKE2FS(8) - john meister © 2015

MKE2FS(8) MKE2FS(8)

NAME
mke2fs - create an ext2/ext3/ext4 filesystem

SYNOPSIS
mke2fs [ -c | -l filename ] [ -b block-size ] [ -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 ] device [
blocks-count ]

mke2fs -O journal_dev [ -b block-size ] [ -L volume-label ] [ -n ] [ -q ] [ -v ] external-journal [ blocks-count ]

DESCRIPTION
mke2fs is used to create an ext2, ext3, or ext4 filesystem, usually in a disk partition. device is the special file corre‐
sponding to the device (e.g /dev/hdXX). blocks-count is the number of blocks on the device. If omitted, mke2fs automagi‐
cally figures the file system size. If called as mkfs.ext3 a journal is created as if the -j option was specified.

The defaults of the parameters for the newly created filesystem, if not overridden by the options listed below, are con‐
trolled 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.

-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 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. 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 fea‐
ture 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 typi‐
cally 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.

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 ini‐
tializing 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 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.

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 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 filesystem initialization. This is set as default.

nodiscard
Do not attempt to discard blocks at mkfs time.

quotatype
Specify which quota type ('usr' or 'grp') is to be initialized. This option has any effect only if quota
feature is set. Without this extended option, the default behavior is to initialize both user and group
quotas.

-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 parame‐
ter, 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.

-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 expand the number of inodes on a filesystem after it is created, so be careful deciding the
correct value for this parameter.

-I inode-size
Specify the size of each inode in bytes. mke2fs creates 256-byte inodes by default. 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. 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 nega‐
tively impact 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. It is not possible to change this value after the
filesystem is created.

-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)

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 parame‐
ters 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 pre‐
vented 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 set‐
ting 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 dis‐
able a feature, simply prefix the feature name with a caret ('^') character. The pseudo-filesystem feature "none"
will clear all filesystem features.

dir_index
Use hashed b-trees to speed up lookups in large directories.

extent Instead of using the indirect block scheme for storing the location of data blocks in an inode, use
extents instead. This is a much more efficient encoding which speeds up filesystem access, especially
for large files.

filetype
Store file type information in directory entries.

flex_bg
Allow the per-block group metadata (allocation bitmaps and inode tables) to be placed anywhere on the
storage media. In addition, mke2fs will place the per-block group metadata together starting at the
first block group of each "flex_bg group". The size of the flex_bg group can be specified using the -G
option.

has_journal
Create an ext3 journal (as if using the -j option).

journal_dev
Create an external ext3 journal on the given device instead of a regular ext2 filesystem. Note that
external-journal must be created with the same block size as the filesystems that will be using it.

large_file
Filesystem can contain files that are greater than 2GB. (Modern kernels set this feature automatically
when a file > 2GB is created.)

quota Create quota inodes (inode# 3 for userquota and inode# 4 for group quota) and set them in the
superblock. With this feature, the quotas will be enabled automatically when the filesystem is mounted.

resize_inode
Reserve space so the block group descriptor table may grow in the future. Useful for online resizing
using resize2fs. By default mke2fs will attempt to reserve enough space so that the filesystem may grow
to 1024 times its initial size. This can be changed using the resize extended option.

sparse_super
Create a filesystem with fewer superblock backup copies (saves space on large filesystems).

uninit_bg
Create a filesystem without initializing all of the block groups. This feature also enables checksums
and highest-inode-used statistics in each blockgroup. This feature can speed up filesystem creation
time noticeably (if lazy_itable_init is enabled), and can also reduce e2fsck time dramatically. It is
only supported by the ext4 filesystem in recent Linux kernels.

-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 useful if all of the superblock and backup superblocks are
corrupted, and a last-ditch recovery method is desired. 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. It is critical
to specify the correct filesystem blocksize when using this option, or there is no chance of recovery.

-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(5) file. This option controls which filesys‐
tem options are used by default, based on the fstypes configuration stanza in /etc/mke2fs.conf(5).

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(5). 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 or equal to 3 megabytes, mke2fs will use the filesystem type
floppy. If the filesystem size is greater than 3 but less than or equal to 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.

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 ini‐
tialization.

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 debug‐
ging 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 .

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)

E2fsprogs version 1.42.5 July 2012 MKE2FS(8)

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