Copyright 2006 by Theodore Ts'o. All Rights Reserved.
This file may be copied under the terms of the GNU Public License.
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.
Tags can be assigned multiple values
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: "\en" (for the newline character), "\et" (for the tab character), "\eb" (for the backspace character), and "\e\e" (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 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 filesystem types. The filesystem type can be specified explicitly using the -T option to mke2fs (8).
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).
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 create an undo file.
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 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 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 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 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.
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.
/etc/mke2fs.conf The configuration file for mke2fs (8).
