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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 de- fault 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 sec- tions, 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 charac- ter. 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 rec- ognizing ``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 de- scribed in more detail in future sections of this document. [options] Contains relations which influence how mke2fs(8) behaves. [defaults] Contains relations which define the default parameters used by mke2fs(8). In general, these defaults may be overridden by a defin- ition 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 us- age type can be specified explicitly using the -t and -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(8) 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(8) 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 default value is the OS for which the mke2fs(8) 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(8) 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 jour- nal 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(8) will not create an undo file. In addition, any tags that can be specified in a per-file system tags sub- section 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 section 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), respectively. The mke2fs(8) 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(8) 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 ex- ample, 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 cumula- tive. 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 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 re- quests 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 features 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 op- tion 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 en- abled 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 block size 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 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 ini- tialization 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 su- perblocks. packed_meta_blocks This boolean relation specifies whether the allocation bitmaps, in- ode 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 ac- cepted 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 op- tion, etc.), the data blocks of the pre-allocated files will be con- tiguous. 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 huge- files_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 rela- tion is not specified, the default is to fill the entire file sys- tem. 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(8)). The default value is false, which will cause hugefile alignment to be relative to the be- ginning 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(8) will issue a warn- ing when creating a file system with 128 byte inodes (and so there- fore 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 de- fault, zero blocks will be written to the huge files to avoid stale data from being made available to potentially untrusted user pro- grams, unless the device supports a discard/trim operation which will take care of zeroing the device blocks. By setting zero_huge- files to false, this step will always be skipped, which can be use- ful 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 case- fold 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 encod- ing-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 de- faults 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 1.47.4 March 2025 mke2fs.conf(5)
NAME | DESCRIPTION | THE [options] STANZA | THE [defaults] STANZA | THE [fs_types] STANZA | THE [devices] STANZA | FILES | SEE ALSO
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