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1.\" -*- nroff -*-
2.\" Copyright 1993, 1994, 1995 by Theodore Ts'o. All Rights Reserved.
3.\" This file may be copied under the terms of the GNU Public License.
4.\"
5.TH MKE2FS 8 "@E2FSPROGS_MONTH@ @E2FSPROGS_YEAR@" "E2fsprogs version @E2FSPROGS_VERSION@"
6.SH NAME
7mke2fs \- create an ext2/ext3/ext4 filesystem
8.SH SYNOPSIS
9.B mke2fs
10[
11.B \-c
12|
13.B \-l
14.I filename
15]
16[
17.B \-b
18.I block-size
19]
20[
21.B \-C
22.I cluster-size
23]
24[
25.B \-d
26.I root-directory
27]
28[
29.B \-D
30]
31[
32.B \-g
33.I blocks-per-group
34]
35[
36.B \-G
37.I number-of-groups
38]
39[
40.B \-i
41.I bytes-per-inode
42]
43[
44.B \-I
45.I inode-size
46]
47[
48.B \-j
49]
50[
51.B \-J
52.I journal-options
53]
54[
55.B \-N
56.I number-of-inodes
57]
58[
59.B \-n
60]
61[
62.B \-m
63.I reserved-blocks-percentage
64]
65[
66.B \-o
67.I creator-os
68]
69[
70.B \-O
71[^]\fIfeature\fR[,...]
72]
73[
74.B \-q
75]
76[
77.B \-r
78.I fs-revision-level
79]
80[
81.B \-E
82.I extended-options
83]
84[
85.B \-v
86]
87[
88.B \-F
89]
90[
91.B \-L
92.I volume-label
93]
94[
95.B \-M
96.I last-mounted-directory
97]
98[
99.B \-S
100]
101[
102.B \-t
103.I fs-type
104]
105[
106.B \-T
107.I usage-type
108]
109[
110.B \-U
111.I UUID
112]
113[
114.B \-V
115]
116[
117.B \-e
118.I errors-behavior
119]
120[
121.B \-z
122.I undo_file
123]
124.I device
125[
126.I fs-size
127]
128@JDEV@.sp
129@JDEV@.B "mke2fs \-O journal_dev"
130@JDEV@[
131@JDEV@.B \-b
132@JDEV@.I block-size
133@JDEV@]
134.\" No external-journal specific journal options yet (size is ignored)
135.\" @JDEV@[
136.\" @JDEV@.B \-J
137.\" @JDEV@.I journal-options
138.\" @JDEV@]
139@JDEV@[
140@JDEV@.B \-L
141@JDEV@.I volume-label
142@JDEV@]
143@JDEV@[
144@JDEV@.B \-n
145@JDEV@]
146@JDEV@[
147@JDEV@.B \-q
148@JDEV@]
149@JDEV@[
150@JDEV@.B \-v
151@JDEV@]
152@JDEV@.I external-journal
153@JDEV@[
154@JDEV@.I fs-size
155@JDEV@]
156.SH DESCRIPTION
157.B mke2fs
158is used to create an ext2, ext3, or ext4 filesystem, usually in a disk
159partition (or file) named by
160.IR device .
161.PP
162The file system size is specified by
163.IR fs-size .
164If
165.I fs-size
166does not have a suffix, it is interpreted as power-of-two kilobytes,
167unless the
168.B \-b
169.I blocksize
170option is specified, in which case
171.I fs-size
172is interpreted as the number of
173.I blocksize
174blocks. If the fs-size is suffixed by 'k', 'm', 'g', 't'
175(either upper-case or lower-case), then it is interpreted in
176power-of-two kilobytes, megabytes, gigabytes, terabytes, etc.
177If
178.I fs-size
179is omitted,
180.B mke2fs
181will create the file system based on the device size.
182.PP
183If
184.B mke2fs
185is run as
186.B mkfs.XXX
187(i.e.,
188.BR mkfs.ext2 ,
189.BR mkfs.ext3 ,
190or
191.BR mkfs.ext4 )
192the option
193.B \-t
194.I XXX
195is implied; so
196.B mkfs.ext3
197will create a file system for use with ext3,
198.B mkfs.ext4
199will create a file system for use with ext4, and so on.
200.PP
201The defaults of the parameters for the newly created filesystem, if not
202overridden by the options listed below, are controlled by the
203.B /etc/mke2fs.conf
204configuration file. See the
205.BR mke2fs.conf (5)
206manual page for more details.
207.SH OPTIONS
208.TP
209.BI \-b " block-size"
210Specify the size of blocks in bytes. Valid block-size values are 1024,
2112048 and 4096 bytes per block. If omitted,
212block-size is heuristically determined by the filesystem size and
213the expected usage of the filesystem (see the
214.B \-T
215option). If
216.I block-size
217is preceded by a negative sign ('-'), then
218.B mke2fs
219will use heuristics to determine the
220appropriate block size, with the constraint that the block size will be
221at least
222.I block-size
223bytes. This is useful for certain hardware devices which require that
224the blocksize be a multiple of 2k.
225.TP
226.B \-c
227Check the device for bad blocks before creating the file system. If
228this option is specified twice, then a slower read-write
229test is used instead of a fast read-only test.
230.TP
231.B \-C " cluster-size"
232Specify the size of cluster in bytes for filesystems using the bigalloc
233feature. Valid cluster-size values are from 2048 to 256M bytes per
234cluster. This can only be specified if the bigalloc feature is
235enabled. (See the
236.B ext4 (5)
237man page for more details about bigalloc.) The default cluster size if
238bigalloc is enabled is 16 times the block size.
239.TP
240.BI \-d " root-directory"
241Copy the contents of the given directory into the root directory of the
242filesystem.
243.TP
244.B \-D
245Use direct I/O when writing to the disk. This avoids mke2fs dirtying a
246lot of buffer cache memory, which may impact other applications running
247on a busy server. This option will cause mke2fs to run much more
248slowly, however, so there is a tradeoff to using direct I/O.
249.TP
250.BI \-e " error-behavior"
251Change the behavior of the kernel code when errors are detected.
252In all cases, a filesystem error will cause
253.BR e2fsck (8)
254to check the filesystem on the next boot.
255.I error-behavior
256can be one of the following:
257.RS 1.2i
258.TP 1.2i
259.B continue
260Continue normal execution.
261.TP
262.B remount-ro
263Remount filesystem read-only.
264.TP
265.B panic
266Cause a kernel panic.
267.RE
268.TP
269.BI \-E " extended-options"
270Set extended options for the filesystem. Extended options are comma
271separated, and may take an argument using the equals ('=') sign. The
272.B \-E
273option used to be
274.B \-R
275in earlier versions of
276.BR mke2fs .
277The
278.B \-R
279option is still accepted for backwards compatibility, but is deprecated.
280The following extended options are supported:
281.RS 1.2i
282.TP
283.BI encoding= encoding-name
284Enable the
285.I casefold
286feature in the super block and set
287.I encoding-name
288as the encoding to be used. If
289.I encoding-name
290is not specified, the encoding defined in
291.BR mke2fs.conf (5)
292is used.
293.TP
294.BI encoding_flags= encoding-flags
295Define parameters for file name character encoding operations. If a
296flag is not changed using this parameter, its default value is used.
297.I encoding-flags
298should be a comma-separated lists of flags to be enabled. To disable a
299flag, add it to the list with the prefix "no".
300
301The only flag that can be set right now is
302.I strict
303which means that invalid strings should be rejected by the file system.
304In the default configuration, the
305.I strict
306flag is disabled.
307.TP
308.BI mmp_update_interval= interval
309Adjust the initial MMP update interval to
310.I interval
311seconds. Specifying an
312.I interval
313of 0 means to use the default interval. The specified interval must
314be less than 300 seconds. Requires that the
315.B mmp
316feature be enabled.
317.TP
318.BI stride= stride-size
319Configure the filesystem for a RAID array with
320.I stride-size
321filesystem blocks. This is the number of blocks read or written to disk
322before moving to the next disk, which is sometimes referred to as the
323.I chunk size.
324This mostly affects placement of filesystem metadata like bitmaps at
325.B mke2fs
326time to avoid placing them on a single disk, which can hurt performance.
327It may also be used by the block allocator.
328.TP
329.BI stripe_width= stripe-width
330Configure the filesystem for a RAID array with
331.I stripe-width
332filesystem blocks per stripe. This is typically stride-size * N, where
333N is the number of data-bearing disks in the RAID (e.g. for RAID 5 there is one
334parity disk, so N will be the number of disks in the array minus 1).
335This allows the block allocator to prevent read-modify-write of the
336parity in a RAID stripe if possible when the data is written.
337.TP
338.BI offset= offset
339Create the filesystem at an offset from the beginning of the device or
340file. This can be useful when creating disk images for virtual machines.
341.TP
342.BI resize= max-online-resize
343Reserve enough space so that the block group descriptor table can grow
344to support a filesystem that has
345.I max-online-resize
346blocks.
347.TP
348.B lazy_itable_init\fR[\fB= \fI<0 to disable, 1 to enable>\fR]
349If enabled and the uninit_bg feature is enabled, the inode table will
350not be fully initialized by
351.BR mke2fs .
352This speeds up filesystem
353initialization noticeably, but it requires the kernel to finish
354initializing the filesystem in the background when the filesystem is
355first mounted. If the option value is omitted, it defaults to 1 to
356enable lazy inode table zeroing.
357.TP
358.B lazy_journal_init\fR[\fB= \fI<0 to disable, 1 to enable>\fR]
359If enabled, the journal inode will not be fully zeroed out by
360.BR mke2fs .
361This speeds up filesystem initialization noticeably, but carries some
362small risk if the system crashes before the journal has been overwritten
363entirely one time. If the option value is omitted, it defaults to 1 to
364enable lazy journal inode zeroing.
365.TP
366.B no_copy_xattrs
367Normally
368.B mke2fs
369will copy the extended attributes of the files in the directory
370hierarchy specified via the (optional)
371.B \-d
372option. This will disable the copy and leaves the files in the newly
373created file system without any extended attributes.
374.TP
375.BI num_backup_sb= <0|1|2>
376If the
377.B sparse_super2
378file system feature is enabled this option controls whether there will
379be 0, 1, or 2 backup superblocks created in the file system.
380.TP
381.B packed_meta_blocks\fR[\fB= \fI<0 to disable, 1 to enable>\fR]
382Place the allocation bitmaps and the inode table at the beginning of the
383disk. This option requires that the flex_bg file system feature to be
384enabled in order for it to have effect, and will also create the journal
385at the beginning of the file system. This option is useful for flash
386devices that use SLC flash at the beginning of the disk.
387It also maximizes the range of contiguous data blocks, which
388can be useful for certain specialized use cases, such as supported
389Shingled Drives.
390.TP
391.BI root_owner [=uid:gid]
392Specify the numeric user and group ID of the root directory. If no UID:GID
393is specified, use the user and group ID of the user running \fBmke2fs\fR.
394In \fBmke2fs\fR 1.42 and earlier the UID and GID of the root directory were
395set by default to the UID and GID of the user running the mke2fs command.
396The \fBroot_owner=\fR option allows explicitly specifying these values,
397and avoid side-effects for users that do not expect the contents of the
398filesystem to change based on the user running \fBmke2fs\fR.
399.TP
400.B test_fs
401Set a flag in the filesystem superblock indicating that it may be
402mounted using experimental kernel code, such as the ext4dev filesystem.
403.TP
404.B discard
405Attempt to discard blocks at mkfs time (discarding blocks initially is useful
406on solid state devices and sparse / thin-provisioned storage). When the device
407advertises that discard also zeroes data (any subsequent read after the discard
408and before write returns zero), then mark all not-yet-zeroed inode tables as
409zeroed. This significantly speeds up filesystem initialization. This is set
410as default.
411.TP
412.B nodiscard
413Do not attempt to discard blocks at mkfs time.
414.TP
415.B quotatype
416Specify the which quota types (usrquota, grpquota, prjquota) which
417should be enabled in the created file system. The argument of this
418extended option should be a colon separated list. This option has
419effect only if the
420.B quota
421feature is set. The default quota types to be initialized if this
422option is not specified is both user and group quotas. If the project
423feature is enabled that project quotas will be initialized as well.
424.RE
425.TP
426.B \-F
427Force
428.B mke2fs
429to create a filesystem, even if the specified device is not a partition
430on a block special device, or if other parameters do not make sense.
431In order to force
432.B mke2fs
433to create a filesystem even if the filesystem appears to be in use
434or is mounted (a truly dangerous thing to do), this option must be
435specified twice.
436.TP
437.BI \-g " blocks-per-group"
438Specify the number of blocks in a block group. There is generally no
439reason for the user to ever set this parameter, as the default is optimal
440for the filesystem. (For administrators who are creating
441filesystems on RAID arrays, it is preferable to use the
442.I stride
443RAID parameter as part of the
444.B \-E
445option rather than manipulating the number of blocks per group.)
446This option is generally used by developers who
447are developing test cases.
448.IP
449If the bigalloc feature is enabled, the
450.B \-g
451option will specify the number of clusters in a block group.
452.TP
453.BI \-G " number-of-groups"
454Specify the number of block groups that will be packed together to
455create a larger virtual block group (or "flex_bg group") in an
456ext4 filesystem. This improves meta-data locality and performance
457on meta-data heavy workloads. The number of groups must be a power
458of 2 and may only be specified if the
459.B flex_bg
460filesystem feature is enabled.
461.TP
462.BI \-i " bytes-per-inode"
463Specify the bytes/inode ratio.
464.B mke2fs
465creates an inode for every
466.I bytes-per-inode
467bytes of space on the disk. The larger the
468.I bytes-per-inode
469ratio, the fewer inodes will be created. This value generally shouldn't
470be smaller than the blocksize of the filesystem, since in that case more
471inodes would be made than can ever be used. Be warned that it is not
472possible to change this ratio on a filesystem after it is created, so be
473careful deciding the correct value for this parameter. Note that resizing
474a filesystem changes the number of inodes to maintain this ratio.
475.TP
476.BI \-I " inode-size"
477Specify the size of each inode in bytes.
478The
479.I inode-size
480value must be a power of 2 larger or equal to 128. The larger the
481.I inode-size
482the more space the inode table will consume, and this reduces the usable
483space in the filesystem and can also negatively impact performance.
484It is not
485possible to change this value after the filesystem is created.
486.IP
487In kernels after 2.6.10 and some
488earlier vendor kernels it is possible to utilize inodes larger than
489128 bytes to store
490extended attributes for improved performance.
491Extended attributes
492stored in large inodes are not visible with older kernels, and such
493filesystems will not be mountable with 2.4 kernels at all.
494.IP
495The default inode size is controlled by the
496.BR mke2fs.conf (5)
497file. In the
498.B mke2fs.conf
499file shipped with e2fsprogs, the default inode size is 256 bytes for
500most file systems, except for small file systems where the inode size
501will be 128 bytes.
502.TP
503.B \-j
504Create the filesystem with an ext3 journal. If the
505.B \-J
506option is not specified, the default journal parameters will be used to
507create an appropriately sized journal (given the size of the filesystem)
508stored within the filesystem. Note that you must be using a kernel
509which has ext3 support in order to actually make use of the journal.
510.TP
511.BI \-J " journal-options"
512Create the ext3 journal using options specified on the command-line.
513Journal options are comma
514separated, and may take an argument using the equals ('=') sign.
515The following journal options are supported:
516.RS 1.2i
517.TP
518.BI size= journal-size
519Create an internal journal (i.e., stored inside the filesystem) of size
520.I journal-size
521megabytes.
522The size of the journal must be at least 1024 filesystem blocks
523(i.e., 1MB if using 1k blocks, 4MB if using 4k blocks, etc.)
524and may be no more than 10,240,000 filesystem blocks or half the total
525file system size (whichever is smaller)
526.TP
527.BI location =journal-location
528Specify the location of the journal. The argument
529.I journal-location
530can either be specified as a block number, or if the number has a units
531suffix (e.g., 'M', 'G', etc.) interpret it as the offset from the
532beginning of the file system.
533@JDEV@.TP
534@JDEV@.BI device= external-journal
535@JDEV@Attach the filesystem to the journal block device located on
536@JDEV@.IR external-journal .
537@JDEV@The external
538@JDEV@journal must already have been created using the command
539@JDEV@.IP
540@JDEV@.B mke2fs -O journal_dev
541@JDEV@.I external-journal
542@JDEV@.IP
543@JDEV@Note that
544@JDEV@.I external-journal
545@JDEV@must have been created with the
546@JDEV@same block size as the new filesystem.
547@JDEV@In addition, while there is support for attaching
548@JDEV@multiple filesystems to a single external journal,
549@JDEV@the Linux kernel and
550@JDEV@.BR e2fsck (8)
551@JDEV@do not currently support shared external journals yet.
552@JDEV@.IP
553@JDEV@Instead of specifying a device name directly,
554@JDEV@.I external-journal
555@JDEV@can also be specified by either
556@JDEV@.BI LABEL= label
557@JDEV@or
558@JDEV@.BI UUID= UUID
559@JDEV@to locate the external journal by either the volume label or UUID
560@JDEV@stored in the ext2 superblock at the start of the journal. Use
561@JDEV@.BR dumpe2fs (8)
562@JDEV@to display a journal device's volume label and UUID. See also the
563@JDEV@.B -L
564@JDEV@option of
565@JDEV@.BR tune2fs (8).
566.RE
567@JDEV@.IP
568@JDEV@Only one of the
569@JDEV@.BR size " or " device
570@JDEV@options can be given for a filesystem.
571.TP
572.BI \-l " filename"
573Read the bad blocks list from
574.IR filename .
575Note that the block numbers in the bad block list must be generated
576using the same block size as used by
577.BR mke2fs .
578As a result, the
579.B \-c
580option to
581.B mke2fs
582is a much simpler and less error-prone method of checking a disk for bad
583blocks before formatting it, as
584.B mke2fs
585will automatically pass the correct parameters to the
586.B badblocks
587program.
588.TP
589.BI \-L " new-volume-label"
590Set the volume label for the filesystem to
591.IR new-volume-label .
592The maximum length of the
593volume label is 16 bytes.
594.TP
595.BI \-m " reserved-blocks-percentage"
596Specify the percentage of the filesystem blocks reserved for
597the super-user. This avoids fragmentation, and allows root-owned
598daemons, such as
599.BR syslogd (8),
600to continue to function correctly after non-privileged processes are
601prevented from writing to the filesystem. The default percentage
602is 5%.
603.TP
604.BI \-M " last-mounted-directory"
605Set the last mounted directory for the filesystem. This might be useful
606for the sake of utilities that key off of the last mounted directory to
607determine where the filesystem should be mounted.
608.TP
609.B \-n
610Causes
611.B mke2fs
612to not actually create a filesystem, but display what it
613would do if it were to create a filesystem. This can be used to
614determine the location of the backup superblocks for a particular
615filesystem, so long as the
616.B mke2fs
617parameters that were passed when the
618filesystem was originally created are used again. (With the
619.B \-n
620option added, of course!)
621.TP
622.BI \-N " number-of-inodes"
623Overrides the default calculation of the number of inodes that should be
624reserved for the filesystem (which is based on the number of blocks and
625the
626.I bytes-per-inode
627ratio). This allows the user to specify the number
628of desired inodes directly.
629.TP
630.BI \-o " creator-os"
631Overrides the default value of the "creator operating system" field of the
632filesystem. The creator field is set by default to the name of the OS the
633.B mke2fs
634executable was compiled for.
635.TP
636.B "\-O \fR[^]\fIfeature\fR[,...]"
637Create a filesystem with the given features (filesystem options),
638overriding the default filesystem options. The features that are
639enabled by default are specified by the
640.I base_features
641relation, either in the
642.I [defaults]
643section in the
644.B /etc/mke2fs.conf
645configuration file,
646or in the
647.I [fs_types]
648subsections for the usage types as specified by the
649.B \-T
650option, further modified by the
651.I features
652relation found in the
653.I [fs_types]
654subsections for the filesystem and usage types. See the
655.BR mke2fs.conf (5)
656manual page for more details.
657The filesystem type-specific configuration setting found in the
658.I [fs_types]
659section will override the global default found in
660.IR [defaults] .
661.sp
662The filesystem feature set will be further edited
663using either the feature set specified by this option,
664or if this option is not given, by the
665.I default_features
666relation for the filesystem type being created, or in the
667.I [defaults]
668section of the configuration file.
669.sp
670The filesystem feature set is comprised of a list of features, separated
671by commas, that are to be enabled. To disable a feature, simply
672prefix the feature name with a caret ('^') character.
673Features with dependencies will not be removed successfully.
674The pseudo-filesystem feature "none" will clear all filesystem features.
675.TP
676For more information about the features which can be set, please see
677the manual page
678.BR ext4 (5).
679.TP
680.B \-q
681Quiet execution. Useful if
682.B mke2fs
683is run in a script.
684.TP
685.BI \-r " revision"
686Set the filesystem revision for the new filesystem. Note that 1.2
687kernels only support revision 0 filesystems. The default is to
688create revision 1 filesystems.
689.TP
690.B \-S
691Write superblock and group descriptors only. This is an extreme
692measure to be taken only in the very unlikely case that all of
693the superblock and backup superblocks are corrupted, and a last-ditch
694recovery method is desired by experienced users. It causes
695.B mke2fs
696to reinitialize the superblock and group descriptors, while not
697touching the inode table and the block and inode bitmaps. The
698.B e2fsck
699program should be run immediately after this option is used, and there
700is no guarantee that any data will be salvageable. Due to the wide
701variety of possible options to
702.B mke2fs
703that affect the on-disk layout, it is critical to specify exactly
704the same format options, such as blocksize, fs-type, feature flags, and
705other tunables when using this option, or the filesystem will be further
706corrupted. In some cases, such as filesystems that have been resized,
707or have had features enabled after format time, it is impossible to
708overwrite all of the superblocks correctly, and at least some filesystem
709corruption will occur. It is best to run this on a full copy of the
710filesystem so other options can be tried if this doesn't work.
711.\" .TP
712.\" .BI \-t " test"
713.\" Check the device for bad blocks before creating the file system
714.\" using the specified test.
715.TP
716.BI \-t " fs-type"
717Specify the filesystem type (i.e., ext2, ext3, ext4, etc.) that is
718to be created.
719If this option is not specified,
720.B mke2fs
721will pick a default either via how
722the command was run (for example, using a name of the form mkfs.ext2,
723mkfs.ext3, etc.) or via a default as defined by the
724.B /etc/mke2fs.conf
725file. This option controls which filesystem options are used by
726default, based on the
727.B fstypes
728configuration stanza in
729.BR /etc/mke2fs.conf .
730.sp
731If the
732.B \-O
733option is used to explicitly add or remove filesystem options that
734should be set in the newly created filesystem, the
735resulting filesystem may not be supported by the requested
736.IR fs-type .
737(e.g., "\fBmke2fs \-t ext3 \-O extent /dev/sdXX\fR" will create a
738filesystem that is not supported by the ext3 implementation as found in
739the Linux kernel; and "\fBmke2fs \-t ext3 \-O ^has_journal /dev/hdXX\fR"
740will create a filesystem that does not have a journal and hence will not
741be supported by the ext3 filesystem code in the Linux kernel.)
742.TP
743.BI \-T " usage-type[,...]"
744Specify how the filesystem is going to be used, so that
745.B mke2fs
746can choose optimal filesystem parameters for that use. The usage
747types that are supported are defined in the configuration file
748.BR /etc/mke2fs.conf .
749The user may specify one or more usage types
750using a comma separated list.
751.sp
752If this option is is not specified,
753.B mke2fs
754will pick a single default usage type based on the size of the filesystem to
755be created. If the filesystem size is less than 3 megabytes,
756.B mke2fs
757will use the filesystem type
758.IR floppy .
759If the filesystem size is greater than or equal to 3 but less than
760512 megabytes,
761.BR mke2fs (8)
762will use the filesystem type
763.IR small .
764If the filesystem size is greater than or equal to 4 terabytes but less than
76516 terabytes,
766.BR mke2fs (8)
767will use the filesystem type
768.IR big .
769If the filesystem size is greater than or equal to 16 terabytes,
770.BR mke2fs (8)
771will use the filesystem type
772.IR huge .
773Otherwise,
774.BR mke2fs (8)
775will use the default filesystem type
776.IR default .
777.TP
778.BI \-U " UUID"
779Set the universally unique identifier (UUID) of the filesystem to
780.IR UUID .
781The format of the UUID is a series of hex digits separated by hyphens,
782like this:
783"c1b9d5a2-f162-11cf-9ece-0020afc76f16".
784The
785.I UUID
786parameter may also be one of the following:
787.RS 1.2i
788.TP
789.I clear
790clear the filesystem UUID
791.TP
792.I random
793generate a new randomly-generated UUID
794.TP
795.I time
796generate a new time-based UUID
797.RE
798.TP
799.B \-v
800Verbose execution.
801.TP
802.B \-V
803Print the version number of
804.B mke2fs
805and exit.
806.TP
807.BI \-z " undo_file"
808Before overwriting a file system block, write the old contents of the block to
809an undo file. This undo file can be used with e2undo(8) to restore the old
810contents of the file system should something go wrong. If the empty string is
811passed as the undo_file argument, the undo file will be written to a file named
812mke2fs-\fIdevice\fR.e2undo in the directory specified via the
813\fIE2FSPROGS_UNDO_DIR\fR environment variable or the \fIundo_dir\fR directive
814in the configuration file.
815
816WARNING: The undo file cannot be used to recover from a power or system crash.
817.SH ENVIRONMENT
818.TP
819.B MKE2FS_SYNC
820If set to non-zero integer value, its value is used to determine how often
821.BR sync (2)
822is called during inode table initialization.
823.TP
824.B MKE2FS_CONFIG
825Determines the location of the configuration file (see
826.BR mke2fs.conf (5)).
827.TP
828.B MKE2FS_FIRST_META_BG
829If set to non-zero integer value, its value is used to determine first meta
830block group. This is mostly for debugging purposes.
831.TP
832.B MKE2FS_DEVICE_SECTSIZE
833If set to non-zero integer value, its value is used to determine logical
834sector size of the
835.IR device .
836.TP
837.B MKE2FS_DEVICE_PHYS_SECTSIZE
838If set to non-zero integer value, its value is used to determine physical
839sector size of the
840.IR device .
841.TP
842.B MKE2FS_SKIP_CHECK_MSG
843If set, do not show the message of filesystem automatic check caused by
844mount count or check interval.
845.SH AUTHOR
846This version of
847.B mke2fs
848has been written by Theodore Ts'o <tytso@mit.edu>.
849.SH AVAILABILITY
850.B mke2fs
851is part of the e2fsprogs package and is available from
852http://e2fsprogs.sourceforge.net.
853.SH SEE ALSO
854.BR mke2fs.conf (5),
855.BR badblocks (8),
856.BR dumpe2fs (8),
857.BR e2fsck (8),
858.BR tune2fs (8),
859.BR ext4 (5)