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mke2fs.conf(5) 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 or ext3 filesystems.

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 fur-
ther 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 back-
slash interpretations apply: "\n" (for the newline character), "\t" (for the tab character), "\b" (for the backspace
character), and "\\" (for the backslash character).

The following stanzas are used in the mke2fs.conf file. They will be described in more detail in future sections of this
document.

[defaults]
Contains relations which define the default parameters used by mke2fs(8). In general, these defaults may be over-
ridden 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 filesystem types. The filesystem type
can be specified explicitly using the -T option to mke2fs(8).

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 over-
ridden 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_fea-
tures 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).

force_undo
This relation, if set to a boolean 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 blocksize on the command line, and
the filesystem-type specific section of the configuration 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.

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 cre-
ate an undo file.

THE [fs_types] STANZA
Each tag in the [fs_types] stanza names a filesystem 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 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 correspond-
ing with each entry in the constructed list, with later entries overriding earlier filesystem or usage types. For exam-
ple, 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 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 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 features, and finally the configura-
tion relation fs_types.floppy.features would remove the resize_inode feature, resulting in a filesystem feature set con-
sisting 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 filesystem 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 modify 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 fea-
ture 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.

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).

blocksize
This relation specifies the default blocksize if the user does not specify a blocksize on the command line.

lazy_itable_init
This relation is a boolean which 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 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.

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.

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 goups 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 goups 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-filesystem type basis.

FILES
/etc/mke2fs.conf
The configuration file for mke2fs(8).