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NAME | DESCRIPTION | THE [options] STANZA | THE [defaults] STANZA | THE [fs_types] STANZA | THE [devices] STANZA | FILES | SEE ALSO | COLOPHON |
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mke2fs.conf(5) File Formats Manual mke2fs.conf(5)
mke2fs.conf - Configuration file for mke2fs
mke2fs.conf is the configuration file for mke2fs(8). It controls
the default parameters used by mke2fs(8) when it is creating ext2,
ext3, or ext4 file systems.
The mke2fs.conf file uses an INI-style format. Stanzas, or top-
level sections, are delimited by square braces: [ ]. Within each
section, each line defines a relation, which assigns tags to
values, or to a subsection, which contains further relations or
subsections. An example of the INI-style format used by this
configuration file follows below:
[section1]
tag1 = value_a
tag1 = value_b
tag2 = value_c
[section 2]
tag3 = {
subtag1 = subtag_value_a
subtag1 = subtag_value_b
subtag2 = subtag_value_c
}
tag1 = value_d
tag2 = value_e
}
Comments are delimited by a semicolon (';') or a hash ('#')
character at the beginning of the comment, and are terminated by
the end of line character.
Tags and values must be quoted using double quotes if they contain
spaces. Within a quoted string, the standard backslash
interpretations apply: "\n" (for the newline character), "\t" (for
the tab character), "\b" (for the backspace character), and "\\"
(for the backslash character).
Some relations expect a boolean value. The parser is quite
liberal on recognizing ``yes'', '`y'', ``true'', ``t'', ``1'',
``on'', etc. as a boolean true value, and ``no'', ``n'',
``false'', ``nil'', ``0'', ``off'' as a boolean false value.
The following stanzas are used in the mke2fs.conf file. They will
be described in more detail in future sections of this document.
[options]
Contains relations which influence how mke2fs behaves.
[defaults]
Contains relations which define the default parameters used
by mke2fs(8). In general, these defaults may be overridden
by a definition in the fs_types stanza, or by a command-
line option provided by the user.
[fs_types]
Contains relations which define defaults that should be
used for specific file system and usage types. The file
system type and usage type can be specified explicitly
using the -tand-T options to mke2fs(8), respectively.
[devices]
Contains relations which define defaults for specific
devices.
The following relations are defined in the [options] stanza.
proceed_delay
If this relation is set to a positive integer, then mke2fs
will wait proceed_delay seconds after asking the user for
permission to proceed and then continue, even if the user
has not answered the question. Defaults to 0, which means
to wait until the user answers the question one way or
another.
sync_kludge
If this relation is set to a positive integer, then while
writing the inode table, mke2fs will request the operating
system flush out pending writes to initialize the inode
table every sync_kludge block groups. This is needed to
work around buggy kernels that don't handle writeback
throttling correctly.
The following relations are defined in the [defaults] stanza.
creator_os
This relation specifies the "creator operating system" for
the file system unless it is overridden on the command
line. The default value is the OS for which the mke2fs
executable was compiled.
fs_type
This relation specifies the default file system type if the
user does not specify it via the -t option, or if mke2fs is
not started using a program name of the form mkfs.fs-type.
If both the user and the mke2fs.conf file do not specify a
default file system type, mke2fs will use a default file
system type of ext3 if a journal was requested via a
command-line option, or ext2 if not.
undo_dir
This relation specifies the directory where the undo file
should be stored. It can be overridden via the
E2FSPROGS_UNDO_DIR environment variable. If the directory
location is set to the value none, mke2fs will not create
an undo file.
In addition, any tags that can be specified in a per-file system
tags subsection as defined below (e.g., blocksize, hash_alg,
inode_ratio, inode_size, reserved_ratio, etc.) can also be
specified in the defaults stanza to specify the default value to
be used if the user does not specify one on the command line, and
the file system-type specific section of the configuration file
does not specify a default value.
Each tag in the [fs_types] stanza names a file system type or
usage type which can be specified via the -t or -T options to
mke2fs(8), respectively.
The mke2fs program constructs a list of fs_types by concatenating
the file system type (i.e., ext2, ext3, etc.) with the usage type
list. For most configuration options, mke2fs will look for a
subsection in the [fs_types] stanza corresponding with each entry
in the constructed list, with later entries overriding earlier
file system or usage types. For example, consider the following
mke2fs.conf fragment:
[defaults]
base_features = sparse_super,filetype,resize_inode,dir_index
blocksize = 4096
inode_size = 256
inode_ratio = 16384
[fs_types]
ext3 = {
features = has_journal
}
ext4 = {
features = extents,flex_bg
inode_size = 256
}
small = {
blocksize = 1024
inode_ratio = 4096
}
floppy = {
features = ^resize_inode
blocksize = 1024
inode_size = 128
}
If mke2fs started with a program name of mke2fs.ext4, then the
file system type of ext4 will be used. If the file system is
smaller than 3 megabytes, and no usage type is specified, then
mke2fs will use a default usage type of floppy. This results in
an fs_types list of "ext4, floppy". Both the ext4 subsection and
the floppy subsection define an inode_size relation, but since the
later entries in the fs_types list supersede earlier ones, the
configuration parameter for fs_types.floppy.inode_size will be
used, so the file system will have an inode size of 128.
The exception to this resolution is the features tag, which
specifies a set of changes to the features used by the file
system, and which is cumulative. So in the above example, first
the configuration relation defaults.base_features would enable an
initial feature set with the sparse_super, filetype, resize_inode,
and dir_index features enabled. Then configuration relation
fs_types.ext4.features would enable the extents and flex_bg
features, and finally the configuration relation
fs_types.floppy.features would remove the resize_inode feature,
resulting in a file system feature set consisting of the
sparse_super, filetype, dir_index, extents_and flex_bg features.
For each file system type, the following tags may be used in that
fs_type's subsection. These tags may also be used in the default
section:
base_features
This relation specifies the features which are initially
enabled for this file system type. Only one base_features
will be used, so if there are multiple entries in the
fs_types list whose subsections define the base_features
relation, only the last will be used by mke2fs(8).
enable_periodic_fsck
This boolean relation specifies whether periodic file
system checks should be enforced at boot time. If set to
true, checks will be forced every 180 days, or after a
random number of mounts. These values may be changed later
via the -i and -c command-line options to tune2fs(8).
errors 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.
errors can be one of the following:
continue
Continue normal execution.
remount-ro
Remount file system read-only.
panic Cause a kernel panic.
features
This relation specifies a comma-separated list of features
edit requests which modify the feature set used by the
newly constructed file system. The syntax is the same as
the -O command-line option to mke2fs(8); that is, a feature
can be prefixed by a caret ('^') symbol to disable a named
feature. Each feature relation specified in the fs_types
list will be applied in the order found in the fs_types
list.
force_undo
This boolean relation, if set to a value of true, forces
mke2fs to always try to create an undo file, even if the
undo file might be huge and it might extend the time to
create the file system image because the inode table isn't
being initialized lazily.
default_features
This relation specifies set of features which should be
enabled or disabled after applying the features listed in
the base_features and features relations. It may be
overridden by the -O command-line option to mke2fs(8).
auto_64-bit_support
This relation is a boolean which specifies whether
mke2fs(8) should automatically add the 64bit feature if the
number of blocks for the file system requires this feature
to be enabled. The resize_inode feature is also
automatically disabled since it doesn't support 64-bit
block numbers.
default_mntopts
This relation specifies the set of mount options which
should be enabled by default. These may be changed at a
later time with the -o command-line option to tune2fs(8).
blocksize
This relation specifies the default blocksize if the user
does not specify a blocksize on the command line.
lazy_itable_init
This boolean relation specifies whether the inode table
should be lazily initialized. It only has meaning if the
uninit_bg feature is enabled. If lazy_itable_init is true
and the uninit_bg feature is enabled, the inode table will
not be fully initialized by mke2fs(8). 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.
lazy_journal_init
This boolean relation specifies whether the journal inode
should be lazily initialized. It only has meaning if the
has_journal feature is enabled. If lazy_journal_init is
true, 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.
journal_location
This relation specifies the location of the journal.
num_backup_sb
This relation indicates whether file systems with the
sparse_super2 feature enabled should be created with 0, 1,
or 2 backup superblocks.
packed_meta_blocks
This boolean relation specifies whether the allocation
bitmaps, inode table, and journal should be located at the
beginning of the file system.
inode_ratio
This relation specifies the default inode ratio if the user
does not specify one on the command line.
inode_size
This relation specifies the default inode size if the user
does not specify one on the command line.
reserved_ratio
This relation specifies the default percentage of file
system blocks reserved for the super-user, if the user does
not specify one on the command line.
hash_alg
This relation specifies the default hash algorithm used for
the new file systems with hashed b-tree directories. Valid
algorithms accepted are: legacy, half_md4, and tea.
flex_bg_size
This relation specifies the number of block groups that
will be packed together to create one large virtual block
group on 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.
options
This relation specifies additional extended options which
should be treated by mke2fs(8) as if they were prepended to
the argument of the -E option. This can be used to
configure the default extended options used by mke2fs(8) on
a per-file system type basis.
discard
This boolean relation specifies whether the mke2fs(8)
should attempt to discard device prior to file system
creation.
set_raid_stride
This relation specifies whether the file sytem's RAID
stride size is set from the block device if available.
Valid values are: always, disk, never. The default value
is always.
set_raid_stripe
This relation specifies whether the file sytem's RAID
stripe size is set from the block device if available.
Valid values are: always, disk, never. The default value
is disk.
cluster_size
This relation specifies the default cluster size if the
bigalloc file system feature is enabled. It can be
overridden via the -C command line option to mke2fs(8)
make_hugefiles
This boolean relation enables the creation of pre-allocated
files as part of formatting the file system. The extent
tree blocks for these pre-allocated files will be placed
near the beginning of the file system, so that if all of
the other metadata blocks are also configured to be placed
near the beginning of the file system (by disabling the
backup superblocks, using the packed_meta_blocks option,
etc.), the data blocks of the pre-allocated files will be
contiguous.
hugefiles_dir
This relation specifies the directory where huge files are
created, relative to the file system root.
hugefiles_uid
This relation controls the user ownership for all of the
files and directories created by the make_hugefiles
feature.
hugefiles_gid
This relation controls the group ownership for all of the
files and directories created by the make_hugefiles
feature.
hugefiles_umask
This relation specifies the umask used when creating the
files and directories by the make_hugefiles feature.
num_hugefiles
This relation specifies the number of huge files to be
created. If this relation is not specified, or is set to
zero, and the hugefiles_size relation is non-zero, then
make_hugefiles will create as many huge files as can fit to
fill the entire file system.
hugefiles_slack
This relation specifies how much space should be reserved
for other files.
hugefiles_size
This relation specifies the size of the huge files. If
this relation is not specified, the default is to fill the
entire file system.
hugefiles_align
This relation specifies the alignment for the start block
of the huge files. It also forces the size of huge files
to be a multiple of the requested alignment. If this
relation is not specified, no alignment requirement will be
imposed on the huge files.
hugefiles_align_disk
This relations specifies whether the alignment should be
relative to the beginning of the hard drive (assuming that
the starting offset of the partition is available to
mke2fs). The default value is false, which will cause
hugefile alignment to be relative to the beginning of the
file system.
hugefiles_name
This relation specifies the base file name for the huge
files.
hugefiles_digits
This relation specifies the (zero-padded) width of the
field for the huge file number.
warn_y2038_dates
This boolean relation specifies whether mke2fs will issue a
warning when creating a file system with 128 byte inodes
(and so therefore will not support dates after January
19th, 2038). The default value is true, except for file
systems created for the GNU Hurd since it only supports
128-byte inodes.
zero_hugefiles
This boolean relation specifies whether or not zero blocks
will be written to the hugefiles while mke2fs(8) is
creating them. By default, zero blocks will be written to
the huge files to avoid stale data from being made
available to potentially untrusted user programs, unless
the device supports a discard/trim operation which will
take care of zeroing the device blocks. By setting
zero_hugefiles to false, this step will always be skipped,
which can be useful if it is known that the disk has been
previously erased, or if the user programs that will have
access to the huge files are trusted to not reveal stale
data.
encoding
This relation defines the file name encoding to be used if
the casefold feature is enabled. Currently the only valid
encoding is utf8-12.1 or utf8, which requests the most
recent Unicode version; since 12.1 is the only available
Unicode version, utf8 and utf8-12.1 have the same result.
encoding_flags This relation defines encoding-specific
flags. For utf8 encodings, the only available flag is
strict, which will cause attempts to create file names
containing invalid Unicode characters to be rejected by the
kernel. Strict mode is not enabled by default.
Each tag in the [devices] stanza names device name so that per-
device defaults can be specified.
fs_type
This relation specifies the default parameter for the -t
option, if this option isn't specified on the command line.
usage_types
This relation specifies the default parameter for the -T
option, if this option isn't specified on the command line.
/etc/mke2fs.conf
The configuration file for mke2fs(8).
mke2fs(8)
This page is part of the e2fsprogs (utilities for ext2/3/4
filesystems) project. Information about the project can be found
at ⟨http://e2fsprogs.sourceforge.net/⟩. It is not known how to
report bugs for this man page; if you know, please send a mail to
man-pages@man7.org. This page was obtained from the project's
upstream Git repository
⟨git://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git⟩ on
2025-08-11. (At that time, the date of the most recent commit
that was found in the repository was 2025-07-31.) If you discover
any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page,
or you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a
mail to man-pages@man7.org
E2fsprogs version 1.47.3 July 2025 mke2fs.conf(5)
Pages that refer to this page: ext4(5), mke2fs(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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