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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 jour-
nal-options ] [ -N number-of-inodes ] [ -n ] [ -m reserved-blocks-percentage ] [ -o cre-
ator-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 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 speci-
fied.
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 buf-
fer 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 bit-
maps 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.
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 initial-
ization 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 overwrit-
ten 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 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.
-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 parti-
tion 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 clus-
ters 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 neg-
atively 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 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 con-
tinue to function correctly after non-privileged processes are prevented from writ-
ing 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 filesys-
tem. The creator field is set by default to the name of the OS the mke2fs exe-
cutable 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 configu-
ration 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 ('^') or a minus ('-') character. Features with dependencies will not be
removed successfully. The pseudo-filesystem feature "none" will clear all filesys-
tem 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 guar-
antee 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 com-
mand 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 sup-
ported 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 ter-
abytes, 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 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.source-
forge.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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