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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 filesystems.

The mke2fs.conf file uses an INI-style format. Stanzas, or top-level sections, are delim‐
ited 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 subsec‐
tions. 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 charac‐
ter), "\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 gen‐
eral, these defaults may be overridden by a definition in the fs_types stanza, or
by an command-line option provided by the user.

[fs_types]
Contains relations which define defaults that should be used for specific filesys‐
tem types. The filesystem type can be specified explicitly using the -T option to
mke2fs(8).

THE [options] STANZA
The following relations are defined in the [options] stanza.

proceed_delay
If this relation is set to a positive integer, then if mke2fs will proceed after
waiting proceed_delay seconds, after asking the user for permission to proceed,
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.

THE [defaults] STANZA
The following relations are defined in the [defaults] stanza.

base_features
This relation specifies the filesystems features which are enabled in newly created
filesystems. It may be overridden by the base_features relation found in the
filesystem or usage type subsection of the [fs_types] stanza.

default_features
This relation specifies a set of features that should be added or removed to the
features listed in the base_features relation. It may be overridden by the
filesystem-specific default_features in the filesystem or usage type subsection of
[fs_types], and by the -O command-line option to mke2fs(8).

enable_periodic_fsck
This boolean relation specifies whether periodic filesystem 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).

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 filesystem image because the inode table isn't being initialized
lazily.

fs_type
This relation specifies the default filesystem 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 does not specify a default
filesystem type, mke2fs will use a default filesystem type of ext3 if a journal was
requested via a command-line option, or ext2 if not.

blocksize
This relation specifies the default blocksize if the user does not specify a block‐
size on the command line, and the filesystem-type specific section of the configu‐
ration file does not specify a blocksize.

hash_alg
This relation specifies the default hash algorithm used for the new filesystems
with hashed b-tree directories. Valid algorithms accepted are: legacy, half_md4,
and tea.

inode_ratio
This relation specifies the default inode ratio if the user does not specify one on
the command line, and the filesystem-type specific section of the configuration
file does not specify a default inode ratio.

inode_size
This relation specifies the default inode size if the user does not specify one on
the command line, and the filesystem-type specific section of the configuration
file does not specify a default inode size.

reserved_ratio
This relation specifies the default percentage of filesystem blocks reserved for
the super-user, if the user does not specify one on the command line, and the
filesystem-type specific section of the configuration file does not specify a
default reserved ratio. This value can be a floating point number.

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.

THE [fs_types] STANZA
Each tag in the [fs_types] stanza names a filesystem type or usage type which can be spec‐
ified via the -t or -T options to mke2fs(8), respectively.

The mke2fs program constructs a list of fs_types by concatenating the filesystem 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 filesystem 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 filesystem type of ext4
will be used. If the filesystem is smaller than 3 megabytes, and no usage type is speci‐
fied, 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
filesystem will have an inode size of 128.

The exception to this resolution is the features tag, which is specifies a set of changes
to the features used by the filesystem, 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 fea‐
tures, and finally the configuration relation fs_types.floppy.features would remove the
resize_inode feature, resulting in a filesystem feature set consisting of the
sparse_super, filetype, resize_inode, dir_index, extents_and flex_bg features.

For each filesystem type, the following tags may be used in that fs_type's subsection:

base_features
This relation specifies the features which are initially enabled for this filesys‐
tem 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).

features
This relation specifies a comma-separated list of features edit requests which mod‐
ify the feature set used by the newly constructed filesystem. 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 speci‐
fied in the fs_types list will be applied in the order found in the fs_types list.

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 block‐
size on the command line.

lazy_itable_init
This boolean relation specifies whether the inode table should be lazily initial‐
ized. 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 fully initialized by mke2fs(8). This speeds up filesystem initialization
noticeably, but it requires the kernel to finish initializing the filesystem in the
background when the filesystem is first mounted.

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 specifes 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 filesystem 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 filesystems
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 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.

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-filesys‐
tem type basis.

discard
This boolean relation specifies whether the mke2fs(8) should attempt to discard
device prior to filesystem creation.

cluster_size
This relation specifies the default cluster size if the bigalloc file system fea‐
ture 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 for‐
matting the file system.

hugefiles_uid
This relation controls the user ownership for all of the files and directories cre‐
ated 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 speci‐
fied, 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
Thie 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 if 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 num‐
ber.

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 writ‐
ten 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 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.

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).