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 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 spe‐
cial 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 block‐
size 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 argu‐
ment 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.
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 initial‐
ized 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 zero‐
ing.
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 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 experimen‐
tal 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 dis‐
card 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 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
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 filesys‐
tem 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 sepa‐
rated, and may take an argument using the equals ('=') sign. The following journal options are sup‐
ported:
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 filesys‐
tem 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 exter‐
nal 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 dis‐
play 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.
Specify the percentage of the filesystem blocks reserved for the super-user. This avoids fragmenta‐
tion, 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 cre‐
ated 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 spec‐
ify 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 ('^') 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 reinitial‐
ize 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
mentation 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 <[email protected]>.
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
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