MKE2FS(8) System Manager's Manual 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 fea-
ture[,...] ] [ -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 corresponding to the
device (e.g /dev/hdXX). blocks-count is the number of blocks on the
device. If omitted, mke2fs automagically 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 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 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 compati-
bility, 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 allo-
cator.
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 writ-
ten.
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.
root_owner[=uid:gid]
Specify the numeric user and group ID of the root
directory. If no UID:GID is specified, use the user
and group ID of the user running mke2fs. In mke2fs
1.42 and earlier the UID and GID of the root direc-
tory were set by default to the UID and GID of the
user running the mke2fs command. The root_owner=
option allows explicitly specifying these values,
and avoid side-effects for users that do not expect
the contents of the 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.
-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 cre-
ate 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 gener-
ally 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 per-
formance on meta-data heavy workloads. The number of groups
must be a power of 2 and may only be specified if the flex_bg
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 main-
tain 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 nega-
tively 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)
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 mul-
tiple 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, exter-
nal-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 auto-
matically 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 fea-
tures that are enabled by default are specified by the base_fea-
tures relation, either in the [defaults] section in the
/etc/mke2fs.conf configuration file, or in the [fs_types] sub-
sections for the usage types as specified by the -T option, fur-
ther modified by the features relation found in the [fs_types]
subsections for the 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] sec-
tion 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 configu-
ration file.
The filesystem 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 ('^') or a
minus ('-') 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 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 salvage-
able. It is critical to specify the correct filesystem block-
size 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 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 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 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 AT mit.edu>.
BUGS
mke2fs accepts the -f option but currently ignores it because the sec-
ond 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)
E2fsprogs version 1.42.9 December 2013 MKE2FS(8)
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