mke2fs.conf(5) File Formats Manual mke2fs.conf(5)
NAME
mke2fs.conf - Configuration file for mke2fs
DESCRIPTION
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 sub-
section, 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 charac-
ter).
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 de-
finition in the fs_types stanza, or by a command-line option pro-
vided 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 [options] STANZA
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 [defaults] STANZA
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 de-
fault value is the OS for which the mke2fs executable was com-
piled.
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 envi-
ronment 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, in-
ode_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 sec-
tion of the configuration file does not specify a default value.
THE [fs_types] STANZA
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), respec-
tively.
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 sys-
tem 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 de-
fault 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 cu-
mulative. So in the above example, first the configuration relation de-
faults.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 ex-
tents and flex_bg features, and finally the configuration relation
fs_types.floppy.features would remove the resize_inode feature, result-
ing in a file system feature set consisting of the sparse_super, file-
type, 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 sec-
tion:
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 sub-
sections 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 com-
mand-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 fol-
lowing:
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 con-
structed 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 re-
lation specified in the fs_types list will be applied in the or-
der 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_fea-
tures 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 fea-
ture is enabled, the inode table will not be fully initialized
by mke2fs(8). This speeds up file system initialization notice-
ably, 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 in-
ode 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 en-
tirely one time.
journal_location
This relation specifies the location of the journal.
num_backup_sb
This relation indicates whether file systems with the sparse_su-
per2 feature enabled should be created with 0, 1, or 2 backup su-
perblocks.
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 algo-
rithms 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 perfor-
mance 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 ex-
tended options used by mke2fs(8) on a per-file system type basis.
discard
This boolean relation specifies whether the mke2fs(8) should at-
tempt to discard device prior to file system creation.
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-al-
located files will be contiguous.
hugefiles_dir
This relation specifies the directory where huge files are cre-
ated, 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 sys-
tem.
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 re-
lation 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 multi-
ple of the requested alignment. If this relation is not speci-
fied, 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 rela-
tive 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 warn-
ing 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 opera-
tion which will take care of zeroing the device blocks. By set-
ting zero_hugefiles to false, this step will always be skipped,
which can be useful if it is known that the disk has been previ-
ously 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 ver-
sion; since 12.1 is the only available Unicode version, utf8 and
utf8-12.1 have the same result. encoding_flags This relation de-
fines 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.
THE [devices] STANZA
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.
FILES
/etc/mke2fs.conf
The configuration file for mke2fs(8).
SEE ALSO
mke2fs(8)
E2fsprogs version 1.47.2 January 2025 mke2fs.conf(5)
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