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 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 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 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 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 requests 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 feature 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 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 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 initialization
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 superblocks.
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 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 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.
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-allocated files will be contiguous.
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 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 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 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). The default value is false, which 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 number.
warn_y2038_dates
This boolean relation specifies wheather mke2fs will issue
a warning 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 operation which will
take care of zeroing the device blocks. By setting
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.
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 version; since 12.1 is the only
available Unicode version, utf8 and utf8-12.1 have the
same result. encoding_flags This relation defines
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.
