-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 systems
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 usage 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 system.
-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 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 compatibility, 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
encoding 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 enabled. 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 invalid 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 interval 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 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 file system for a RAID array
with stripe-width file system 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
machines.
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 initialization noticeably, but it
requires the kernel to finish initializing 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 overwritten
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 controls 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 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 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 system.
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 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
extended option should be a colon separated
list. This option has effect only if the
quota feature is set. The default quota
types to be initialized if this option is not
specified is both user and group quotas. If
the project feature is enabled that project
quotas will be initialized as well.
-F Force mke2fs to create a file system, 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 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 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 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 after 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
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 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 January 19, 2038. Inodes which
are 256 bytes or larger will support extended timestamps,
project id's, and the ability to store some extended
attributes in the inode 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 journal
(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 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 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 beginning
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 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
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 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 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 continue to
function correctly after non-privileged processes are
prevented from writing 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 executable
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 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 file system
and usage types. See the mke2fs.conf(5) manual page for
more details. The file system type-specific configuration
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 commas, 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 successfully. The pseudo-file system
feature "none" will clear all file system 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 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 superblocks 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 guarantee that any data will be
salvageable. Due to the wide variety of possible options
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 tunables 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 enabled after format
time, it is impossible to overwrite all of the superblocks
correctly, 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
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
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 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 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 format 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-device.e2undo in
the directory specified via the E2FSPROGS_UNDO_DIR
environment variable or the undo_dir directive in the
configuration file.
WARNING: The undo file cannot be used to recover from a
power or system crash.
