-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.
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-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.
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-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 compatibility. 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.
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-f fragment-size
Specify the size of fragments in bytes.
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-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.
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-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.
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-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.
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-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 expand the
number of inodes on a filesystem after it is created, so be careful deciding the correct value for
this parameter.
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-I inode-size
Specify the size of each inode in bytes. mke2fs creates 256-byte inodes by default. 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. 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. 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. It is not possible to change this
value after the filesystem is created.
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-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.
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-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:
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-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.
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-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.
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-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%.
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-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.
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-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!)
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-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.
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-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.
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-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].
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-q Quiet execution. Useful if mke2fs is run in a script.
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-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.
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-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 salvageable. It is critical to specify the
correct filesystem blocksize when using this option, or there is no chance of recovery.
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-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(5) file. This option controls which filesystem options are used by default,
based on the fstypes configuration stanza in /etc/mke2fs.conf(5).
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.)
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-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(5). 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.
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-U UUID
Create the filesystem with the specified UUID.
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-v Verbose execution.
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-V Print the version number of mke2fs and exit.
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