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MKE2FS(8) System Manager's Manual MKE2FS(8)
NAME
mke2fs - create an ext2/ext3/ext4 file system
SYNOPSIS
mke2fs [ -c | -l filename ] [ -b block-size ] [ -C cluster-size ] [ -d root-directory ] [
-D ] [ -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 file system, 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 cre-
ate a file system for use with ext4, and so on.
The defaults of the parameters for the newly created file system, 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 powers of two
from 1024 up to 65536 (however note that the kernel is able to mount only file sys-
tems with block-size smaller or equal to the system page size - 4k on x86 systems,
up to 64k on ppc64 or aarch64 depending on kernel configuration). If omitted,
block-size is heuristically determined by the file system size and the expected us-
age of the file system (see the -T option). In most common cases, the default
block size is 4k. 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 file systems 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 file sys-
tem.
-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 error-behavior
Change the behavior of the kernel code when errors are detected. In all cases, a
file system error will cause e2fsck(8) to check the file system on the next boot.
error-behavior can be one of the following:
continue Continue normal execution.
remount-ro Remount file system read-only.
panic Cause a kernel panic.
-E extended-options
Set extended options for the file system. 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 com-
patibility, but is deprecated. The following extended options are supported:
encoding=encoding-name
Enable the casefold feature in the super block and set encoding-name as
the encoding to be used. If encoding-name is not specified, the encod-
ing defined in mke2fs.conf(5) is used.
encoding_flags=encoding-flags
Define parameters for file name character encoding operations. If a
flag is not changed using this parameter, its default value is used.
encoding-flags should be a comma-separated lists of flags to be en-
abled. To disable a flag, add it to the list with the prefix "no".
The only flag that can be set right now is strict which means that in-
valid strings should be rejected by the file system. In the default
configuration, the strict flag is disabled.
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 in-
terval must be less than 300 seconds. Requires that the mmp feature be
enabled.
stride=stride-size
Configure the file system for a RAID array with stride-size file system
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 file system 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 file system for a RAID array with stripe-width file sys-
tem 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 file system at an offset from the beginning of the device or
file. This can be useful when creating disk images for virtual ma-
chines.
resize=max-online-resize
Reserve enough space so that the block group descriptor table can grow
to support a file system 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 file system ini-
tialization noticeably, but it requires the kernel to finish initializ-
ing the file system in the background when the file system 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 file system 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.
no_copy_xattrs
Normally mke2fs will copy the extended attributes of the files in the
directory hierarchy specified via the (optional) -d option. This will
disable the copy and leaves the files in the newly created file system
without any extended attributes.
num_backup_sb=<0|1|2>
If the sparse_super2 file system feature is enabled this option con-
trols 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 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 file system to change based on the user running mke2fs.
test_fs
Set a flag in the file system superblock indicating that it may be
mounted using experimental kernel code, such as the ext4dev file sys-
tem.
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
file system 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 ex-
tended option should be a colon separated list. This option has effect
only if the quota feature is set. The default quota types to be ini-
tialized if this option is not specified is both user and group quotas.
If the project feature is enabled that project quotas will be initial-
ized as well.
-F Force mke2fs to create a file system, 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 file system even if the file system 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 file system.
(For administrators who are creating file systems 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 file system. 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 file system
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 file system, 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 file system af-
ter it is created, so be careful deciding the correct value for this parameter.
Note that resizing a file system changes the number of inodes to maintain this ra-
tio.
-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 file system and can also
negatively impact performance. It is not possible to change this value after the
file system is created.
File systems with an inode size of 128 bytes do not support timestamps beyond Janu-
ary 19, 2038. Inodes which are 256 bytes or larger will support extended time-
stamps, project id's, and the ability to store some extended attributes in the in-
ode table for improved performance.
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 file system with an ext3 journal. If the -J option is not specified,
the default journal parameters will be used to create an appropriately sized jour-
nal (given the size of the file system) stored within the file system. 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 op-
tions 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 file system) of
size journal-size megabytes. The size of the journal must be at least
1024 file system blocks (i.e., 1MB if using 1k blocks, 4MB if using 4k
blocks, etc.) and may be no more than 10,240,000 file system blocks or
half the total file system size (whichever is smaller)
fast_commit_size=fast-commit-size
Create an additional fast commit journal area of size fast-commit-size
kilobytes. This option is only valid if fast_commit feature is enabled
on the file system. If this option is not specified and if fast_commit
feature is turned on, fast commit area size defaults to journal-size /
64 megabytes. The total size of the journal with fast_commit feature
set is journal-size + ( fast-commit-size * 1024) megabytes. The total
journal size may be no more than 10,240,000 file system 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 be-
ginning of the file system.
device=external-journal
Attach the file system 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 file system. In addition, while there is support for
attaching multiple file systems 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 su-
perblock 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 file system.
-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 re-
sult, 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 file system to new-volume-label. The maximum length
of the volume label is 16 bytes.
-m reserved-blocks-percentage
Specify the percentage of the file system 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 file system. The default percentage is 5%.
-M last-mounted-directory
Set the last mounted directory for the file system. This might be useful for the
sake of utilities that key off of the last mounted directory to determine where the
file system should be mounted.
-n Causes mke2fs to not actually create a file system, but display what it would do if
it were to create a file system. This can be used to determine the location of the
backup superblocks for a particular file system, so long as the mke2fs parameters
that were passed when the file system 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 file system (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 file
system. The creator field is set by default to the name of the OS the mke2fs exe-
cutable was compiled for.
-O [^]feature[,...]
Create a file system with the given features (file system options), overriding the
default file system options. The features that are enabled by default are speci-
fied 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 file system and usage types. See the
mke2fs.conf(5) manual page for more details. The file system type-specific config-
uration setting found in the [fs_types] section will override the global default
found in [defaults].
The file system 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 file system type being created, or in the [defaults] section of
the configuration file.
The file system feature set is comprised of a list of features, separated by com-
mas, 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 suc-
cessfully. The pseudo-file system feature "none" will clear all file system fea-
tures.
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 file system revision for the new file system. Note that 1.2 kernels only
support revision 0 file systems. The default is to create revision 1 file systems.
-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 su-
perblocks 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 guar-
antee that any data will be salvageable. Due to the wide variety of possible op-
tions 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 tun-
ables when using this option, or the file system will be further corrupted. In
some cases, such as file systems that have been resized, or have had features en-
abled after format time, it is impossible to overwrite all of the superblocks cor-
rectly, and at least some file system corruption will occur. It is best to run
this on a full copy of the file system so other options can be tried if this
doesn't work.
-t fs-type
Specify the file system 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
file system 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 file system options that
should be set in the newly created file system, the resulting file system may not
be supported by the requested fs-type. (e.g., "mke2fs -t ext3 -O extent /dev/sdXX"
will create a file system 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
file system that does not have a journal and hence will not be supported by the
ext3 file system code in the Linux kernel.)
-T usage-type[,...]
Specify how the file system is going to be used, so that mke2fs can choose optimal
file system parameters for that use. The usage types that are supported are de-
fined 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 file system to be created. If the file system size is
less than 3 megabytes, mke2fs will use the file system type floppy. If the file
system size is greater than or equal to 3 but less than 512 megabytes, mke2fs(8)
will use the file system type small. If the file system size is greater than or
equal to 4 terabytes but less than 16 terabytes, mke2fs(8) will use the file system
type big. If the file system size is greater than or equal to 16 terabytes,
mke2fs(8) will use the file system type huge. Otherwise, mke2fs(8) will use the
default file system type default.
-U UUID
Set the universally unique identifier (UUID) of the file system to UUID. The for-
mat of the UUID is a series of hex digits separated by hyphens, like this:
"c1b9d5a2-f162-11cf-9ece-0020afc76f16". The UUID parameter may also be one of the
following:
clear clear the file system UUID
random generate a new randomly-generated UUID
time generate a new time-based 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-de-
vice.e2undo in the directory specified via the E2FSPROGS_UNDO_DIR environment vari-
able 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 logical sector
size of the device.
MKE2FS_DEVICE_PHYS_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 file system 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>.
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 1.46.5 December 2021 MKE2FS(8)
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