Copyright 1993, 1994, 1995 by Theodore Ts'o. All Rights Reserved.
This file may be copied under the terms of the GNU Public License.
@JDEV@[
@JDEV@.B -J
@JDEV@.I journal-options
@JDEV@]
@JDEV@[ @JDEV@.B -L @JDEV@.I volume-label @JDEV@] @JDEV@[ @JDEV@.B -n @JDEV@] @JDEV@[ @JDEV@.B -q @JDEV@] @JDEV@[ @JDEV@.B -v @JDEV@] @JDEV@.I external-journal @JDEV@[ @JDEV@.I blocks-count @JDEV@]
The defaults of the parameters for the newly created filesystem, if not overridden by the options listed below, are controlled by the /etc/mke2fs.conf configuration file. See the mke2fs.conf (5) manual page for more details.
-b " block-size" Specify the size of blocks in bytes. Valid block-size values are 1024, 2048 and 4096 bytes per block. If omitted, block-size is heuristically determined by the filesystem size and the expected usage of the filesystem (see the -T option). If block-size is preceded by a negative sign ('-'), then mke2fs will use heuristics to determine the appropriate block size, with the constraint that the block size will be at least block-size bytes. This is useful for certain hardware devices which require that the blocksize be a multiple of 2k.
-c Check the device for bad blocks before creating the file system. If this option is specified twice, then a slower read-write test is used instead of a fast read-only test.
-E " extended-options" Set extended options for the filesystem. Extended options are comma separated, and may take an argument using the equals ('=') sign. The -E option used to be -R in earlier versions of mke2fs . The -R option is still accepted for backwards compatibility. The following extended options are supported:
stride= stride-size Configure the filesystem for a RAID array with stride-size filesystem blocks. This is the number of blocks read or written to disk before moving to the next disk, which is sometimes referred to as the chunk size. This mostly affects placement of filesystem metadata like bitmaps at mke2fs time to avoid placing them on a single disk, which can hurt performance. It may also be used by the block allocator.
stripe-width= stripe-width Configure the filesystem for a RAID array with stripe-width filesystem blocks per stripe. This is typically stride-size * N, where N is the number of data-bearing disks in the RAID (e.g. for RAID 5 there is one parity disk, so N will be the number of disks in the array minus 1). This allows the block allocator to prevent read-modify-write of the parity in a RAID stripe if possible when the data is written.
resize= max-online-resize Reserve enough space so that the block group descriptor table can grow to support a filesystem that has max-online-resize blocks.
lazy_itable_init[= <0 to disable, 1 to enable>] If enabled and the uninit_bg feature is enabled, the inode table will not be fully initialized by mke2fs . 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. If the option value is omitted, it defaults to 1 to enable lazy inode table initialization.
test_fs Set a flag in the filesystem superblock indicating that it may be mounted using experimental kernel code, such as the ext4dev filesystem.
discard Attempt to discard blocks at mkfs time (discarding blocks initially is useful on solid state devices and sparse / thin-provisioned storage). When the device advertises that discard also zeroes data (any subsequent read after the discard and before write returns zero), then mark all not-yet-zeroed inode tables as zeroed. This significantly speeds up filesystem initialization. This is set as default.
nodiscard Do not attempt to discard blocks at mkfs time. This is the default.
-f " fragment-size" Specify the size of fragments in bytes.
-F Force mke2fs to create a filesystem, even if the specified device is not a partition on a block special device, or if other parameters do not make sense. In order to force mke2fs to create a filesystem even if the filesystem appears to be in use or is mounted (a truly dangerous thing to do), this option must be specified twice.
-g " blocks-per-group" Specify the number of blocks in a block group. There is generally no reason for the user to ever set this parameter, as the default is optimal for the filesystem. (For administrators who are creating filesystems on RAID arrays, it is preferable to use the stride RAID parameter as part of the -E option rather than manipulating the number of blocks per group.) This option is generally used by developers who are developing test cases.
-G " number-of-groups" Specify the number of block groups that will be packed together to create a larger virtual block group (or "flex_bg group") in 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.
-i " bytes-per-inode" Specify the bytes/inode ratio. mke2fs creates an inode for every bytes-per-inode bytes of space on the disk. The larger the bytes-per-inode ratio, the fewer inodes will be created. This value generally shouldn't be smaller than the blocksize of the filesystem, since in that case more inodes would be made than can ever be used. Be warned that it is not possible to expand the number of inodes on a filesystem after it is created, so be careful deciding the correct value for this parameter.
-I " inode-size" Specify the size of each inode in bytes. mke2fs creates 256-byte inodes by default. In kernels after 2.6.10 and some earlier vendor kernels it is possible to utilize inodes larger than 128 bytes to store extended attributes for improved performance. The inode-size value must be a power of 2 larger or equal to 128. The larger the inode-size the more space the inode table will consume, and this reduces the usable space in the filesystem and can also negatively impact performance. Extended attributes stored in large inodes are not visible with older kernels, and such filesystems will not be mountable with 2.4 kernels at all. It is not possible to change this value after the filesystem is created.
-j Create the filesystem with an ext3 journal. If the -J option is not specified, the default journal parameters will be used to create an appropriately sized journal (given the size of the filesystem) stored within the filesystem. Note that you must be using a kernel which has ext3 support in order to actually make use of the journal.
-J " journal-options" Create the ext3 journal using options specified on the command-line. Journal options are comma separated, and may take an argument using the equals ('=') sign. The following journal options are supported:
size= journal-size Create an internal journal (i.e., stored inside the filesystem) of size journal-size megabytes. The size of the journal must be at least 1024 filesystem blocks (i.e., 1MB if using 1k blocks, 4MB if using 4k blocks, etc.) and may be no more than 102,400 filesystem blocks. @JDEV@.TP @JDEV@.BI device= external-journal @JDEV@Attach the filesystem to the journal block device located on @JDEV@.IR external-journal . @JDEV@The external @JDEV@journal must already have been created using the command @JDEV@.IP @JDEV@.B mke2fs -O journal_dev @JDEV@.I external-journal @JDEV@.IP @JDEV@Note that @JDEV@.I external-journal @JDEV@must have been created with the @JDEV@same block size as the new filesystem. @JDEV@In addition, while there is support for attaching @JDEV@multiple filesystems to a single external journal, @JDEV@the Linux kernel and @JDEV@.BR e2fsck (8) @JDEV@do not currently support shared external journals yet. @JDEV@.IP @JDEV@Instead of specifying a device name directly, @JDEV@.I external-journal @JDEV@can also be specified by either @JDEV@.BI LABEL= label @JDEV@or @JDEV@.BI UUID= UUID @JDEV@to locate the external journal by either the volume label or UUID @JDEV@stored in the ext2 superblock at the start of the journal. Use @JDEV@.BR dumpe2fs (8) @JDEV@to display a journal device's volume label and UUID. See also the @JDEV@.B -L @JDEV@option of @JDEV@.BR tune2fs (8). @JDEV@.IP @JDEV@Only one of the @JDEV@.BR size " or " device @JDEV@options can be given for a filesystem.
-l " filename" Read the bad blocks list from filename . Note that the block numbers in the bad block list must be generated using the same block size as used by mke2fs . As a result, the -c option to mke2fs is a much simpler and less error-prone method of checking a disk for bad blocks before formatting it, as mke2fs will automatically pass the correct parameters to the badblocks program.
-L " new-volume-label" Set the volume label for the filesystem to new-volume-label . The maximum length of the volume label is 16 bytes.
-m " reserved-blocks-percentage" Specify the percentage of the filesystem blocks reserved for the super-user. This avoids fragmentation, and allows root-owned daemons, such as syslogd (8), to continue to function correctly after non-privileged processes are prevented from writing to the filesystem. The default percentage is 5%.
-M " last-mounted-directory" Set the last mounted directory for the filesystem. This might be useful for the sake of utilities that key off of the last mounted directory to determine where the filesystem should be mounted.
-n Causes mke2fs to not actually create a filesystem, but display what it would do if it were to create a filesystem. This can be used to determine the location of the backup superblocks for a particular filesystem, so long as the mke2fs parameters that were passed when the filesystem was originally created are used again. (With the -n option added, of course!)
-N " number-of-inodes" Overrides the default calculation of the number of inodes that should be reserved for the filesystem (which is based on the number of blocks and the bytes-per-inode ratio). This allows the user to specify the number of desired inodes directly.
-o " creator-os" Overrides the default value of the "creator operating system" field of the filesystem. The creator field is set by default to the name of the OS the mke2fs executable was compiled for.
"-O feature[,...]" Create a filesystem with the given features (filesystem options), overriding the default filesystem options. The features that are enabled by default are specified by the base_features relation, either in the [defaults] section in the /etc/mke2fs.conf configuration file, or in the [fs_types] subsections for the usage types as specified by the -T option, further modified by the features relation found in the [fs_types] subsections for the filesystem and usage types. See the mke2fs.conf (5) manual page for more details. The filesystem type-specific configuration setting found in the [fs_types] section will override the global default found in [defaults] . The filesystem feature set will be further edited using either the feature set specified by this option, or if this option is not given, by the default_features relation for the filesystem type being created, or in the [defaults] section of the configuration file. The filesystem feature set is comprised of a list of features, separated by commas, that are to be enabled. To disable a feature, simply prefix the feature name with a caret ('^') character. The pseudo-filesystem feature "none" will clear all filesystem features.
dir_index Use hashed b-trees to speed up lookups in large directories.
extent Instead of using the indirect block scheme for storing the location of data blocks in an inode, use extents instead. This is a much more efficient encoding which speeds up filesystem access, especially for large files.
filetype Store file type information in directory entries.
flex_bg Allow the per-block group metadata (allocation bitmaps and inode tables) to be placed anywhere on the storage media. In addition, mke2fs will place the per-block group metadata together starting at the first block group of each "flex_bg group". The size of the flex_bg group can be specified using the -G option.
has_journal Create an ext3 journal (as if using the -j option). @JDEV@.TP @JDEV@.B journal_dev @JDEV@Create an external ext3 journal on the given device @JDEV@instead of a regular ext2 filesystem. @JDEV@Note that @JDEV@.I external-journal @JDEV@must be created with the same @JDEV@block size as the filesystems that will be using it.
large_file Filesystem can contain files that are greater than 2GB. (Modern kernels set this feature automatically when a file > 2GB is created.)
resize_inode Reserve space so the block group descriptor table may grow in the future. Useful for online resizing using resize2fs . By default mke2fs will attempt to reserve enough space so that the filesystem may grow to 1024 times its initial size. This can be changed using the resize extended option.
sparse_super Create a filesystem with fewer superblock backup copies (saves space on large filesystems).
uninit_bg Create a filesystem without initializing all of the block groups. This feature also enables checksums and highest-inode-used statistics in each blockgroup. This feature can speed up filesystem creation time noticeably (if lazy_itable_init is enabled), and can also reduce e2fsck time dramatically. It is only supported by the ext4 filesystem in recent Linux kernels.
-q Quiet execution. Useful if mke2fs is run in a script.
-r " revision" Set the filesystem revision for the new filesystem. Note that 1.2 kernels only support revision 0 filesystems. The default is to create revision 1 filesystems.
-S Write superblock and group descriptors only. This is useful if all of
the superblock and backup superblocks are corrupted, and a last-ditch
recovery method is desired. It causes
mke2fs to reinitialize the
superblock and group descriptors, while not touching the inode table
and the block and inode bitmaps. The
e2fsck program should be run immediately after this option is used, and there
is no guarantee that any data will be salvageable. It is critical to
specify the correct filesystem blocksize when using this option,
or there is no chance of recovery.
.TP
.BI -t " test"
Check the device for bad blocks before creating the file system
using the specified test.
-t " fs-type" Specify the filesystem type (i.e., ext2, ext3, ext4, etc.) that is to be created. If this option is not specified, mke2fs will pick a default either via how the command was run (for example, using a name of the form mkfs.ext2, mkfs.ext3, etc.) or via a default as defined by the /etc/mke2fs.conf (5) file. This option controls which filesystem options are used by default, based on the fstypes configuration stanza in /etc/mke2fs.conf (5). If the -O option is used to explicitly add or remove filesystem options that should be set in the newly created filesystem, the resulting filesystem may not be supported by the requested fs-type . (e.g., "mke2fs -t ext3 -O extents /dev/sdXX" will create a filesystem that is not supported by the ext3 implementation as found in the Linux kernel; and "mke2fs -t ext3 -O ^has_journal /dev/hdXX" will create a filesystem that does not have a journal and hence will not be supported by the ext3 filesystem code in the Linux kernel.)
-T " usage-type[,...]" Specify how the filesystem is going to be used, so that mke2fs can choose optimal filesystem parameters for that use. The usage types that are supported are defined in the configuration file /etc/mke2fs.conf (5). The user may specify one or more usage types using a comma separated list. If this option is is not specified, mke2fs will pick a single default usage type based on the size of the filesystem to be created. If the filesystem size is less than or equal to 3 megabytes, mke2fs will use the filesystem type floppy . If the filesystem size is greater than 3 but less than or equal to 512 megabytes, mke2fs (8) will use the filesystem small . Otherwise, mke2fs (8) will use the default filesystem type default .
-U " UUID" Create the filesystem with the specified UUID.
-v Verbose execution.
-V Print the version number of mke2fs and exit.
