misc/mke2fs.8.in

   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
   7 mke2fs \- 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
 158 is used to create an ext2, ext3, or ext4 filesystem, usually in a disk
 159 partition (or file) named by
 160 .IR device .
 161 .PP
 162 The file system size is specified by
 163 .IR fs-size .
 164 If
 165 .I fs-size
 166 does not have a suffix, it is interpreted as power-of-two kilobytes,
 167 unless the
 168 .B \-b
 169 .I blocksize
 170 option is specified, in which case
 171 .I fs-size
 172 is interpreted as the number of
 173 .I blocksize
 174 blocks.   If the fs-size is suffixed by 'k', 'm', 'g', 't'
 175 (either upper-case or lower-case), then it is interpreted in
 176 power-of-two kilobytes, megabytes, gigabytes, terabytes, etc.
 177 If
 178 .I fs-size
 179 is omitted,
 180 .B mke2fs
 181 will create the file system based on the device size.
 182 .PP
 183 If
 184 .B mke2fs
 185 is run as
 186 .B mkfs.XXX
 187 (i.e.,
 188 .BR mkfs.ext2 ,
 189 .BR mkfs.ext3 ,
 190 or
 191 .BR mkfs.ext4 )
 192 the option
 193 .B \-t
 194 .I XXX
 195 is implied; so
 196 .B mkfs.ext3
 197 will create a file system for use with ext3,
 198 .B mkfs.ext4
 199 will create a file system for use with ext4, and so on.
 200 .PP
 201 The defaults of the parameters for the newly created filesystem, if not
 202 overridden by the options listed below, are controlled by the
 203 .B /etc/mke2fs.conf
 204 configuration file.  See the
 205 .BR mke2fs.conf (5)
 206 manual page for more details.
 207 .SH OPTIONS
 208 .TP
 209 .BI \-b " block-size"
 210 Specify the size of blocks in bytes.  Valid block-size values are 1024,
 211 2048 and 4096 bytes per block.  If omitted,
 212 block-size is heuristically determined by the filesystem size and
 213 the expected usage of the filesystem (see the
 214 .B \-T
 215 option).  If
 216 .I block-size
 217 is preceded by a negative sign ('-'), then
 218 .B mke2fs
 219 will use heuristics to determine the
 220 appropriate block size, with the constraint that the block size will be
 221 at least
 222 .I block-size
 223 bytes.  This is useful for certain hardware devices which require that
 224 the blocksize be a multiple of 2k.
 225 .TP
 226 .B \-c
 227 Check the device for bad blocks before creating the file system.  If
 228 this option is specified twice, then a slower read-write
 229 test is used instead of a fast read-only test.
 230 .TP
 231 .B \-C " cluster-size"
 232 Specify the size of cluster in bytes for filesystems using the bigalloc
 233 feature.  Valid cluster-size values are from 2048 to 256M bytes per
 234 cluster.  This can only be specified if the bigalloc feature is
 235 enabled.  (See the
 236 .B ext4 (5)
 237 man page for more details about bigalloc.)   The default cluster size if
 238 bigalloc is enabled is 16 times the block size.
 239 .TP
 240 .BI \-d " root-directory"
 241 Copy the contents of the given directory into the root directory of the
 242 filesystem.
 243 .TP
 244 .B \-D
 245 Use direct I/O when writing to the disk.  This avoids mke2fs dirtying a
 246 lot of buffer cache memory, which may impact other applications running
 247 on a busy server.  This option will cause mke2fs to run much more
 248 slowly, however, so there is a tradeoff to using direct I/O.
 249 .TP
 250 .BI \-e " error-behavior"
 251 Change the behavior of the kernel code when errors are detected.
 252 In all cases, a filesystem error will cause
 253 .BR e2fsck (8)
 254 to check the filesystem on the next boot.
 255 .I error-behavior
 256 can be one of the following:
 257 .RS 1.2i
 258 .TP 1.2i
 259 .B continue
 260 Continue normal execution.
 261 .TP
 262 .B remount-ro
 263 Remount filesystem read-only.
 264 .TP
 265 .B panic
 266 Cause a kernel panic.
 267 .RE
 268 .TP
 269 .BI \-E " extended-options"
 270 Set extended options for the filesystem.  Extended options are comma
 271 separated, and may take an argument using the equals ('=') sign.  The
 272 .B \-E
 273 option used to be
 274 .B \-R
 275 in earlier versions of
 276 .BR mke2fs .
 277 The
 278 .B \-R
 279 option is still accepted for backwards compatibility, but is deprecated.
 280 The following extended options are supported:
 281 .RS 1.2i
 282 .TP
 283 .BI mmp_update_interval= interval
 284 Adjust the initial MMP update interval to
 285 .I interval
 286 seconds.  Specifying an
 287 .I interval
 288 of 0 means to use the default interval.  The specified interval must
 289 be less than 300 seconds.  Requires that the
 290 .B mmp
 291 feature be enabled.
 292 .TP
 293 .BI stride= stride-size
 294 Configure the filesystem for a RAID array with
 295 .I stride-size
 296 filesystem blocks. This is the number of blocks read or written to disk
 297 before moving to the next disk, which is sometimes referred to as the
 298 .I chunk size.
 299 This mostly affects placement of filesystem metadata like bitmaps at
 300 .B mke2fs
 301 time to avoid placing them on a single disk, which can hurt performance.
 302 It may also be used by the block allocator.
 303 .TP
 304 .BI stripe_width= stripe-width
 305 Configure the filesystem for a RAID array with
 306 .I stripe-width
 307 filesystem blocks per stripe. This is typically stride-size * N, where
 308 N is the number of data-bearing disks in the RAID (e.g. for RAID 5 there is one
 309 parity disk, so N will be the number of disks in the array minus 1).
 310 This allows the block allocator to prevent read-modify-write of the
 311 parity in a RAID stripe if possible when the data is written.
 312 .TP
 313 .BI offset= offset
 314 Create the filesystem at an offset from the beginning of the device or
 315 file.  This can be useful when creating disk images for virtual machines.
 316 .TP
 317 .BI resize= max-online-resize
 318 Reserve enough space so that the block group descriptor table can grow
 319 to support a filesystem that has
 320 .I max-online-resize
 321 blocks.
 322 .TP
 323 .B lazy_itable_init\fR[\fB= \fI<0 to disable, 1 to enable>\fR]
 324 If enabled and the uninit_bg feature is enabled, the inode table will
 325 not be fully initialized by
 326 .BR mke2fs .
 327 This speeds up filesystem
 328 initialization noticeably, but it requires the kernel to finish
 329 initializing the filesystem in the background when the filesystem is
 330 first mounted.  If the option value is omitted, it defaults to 1 to
 331 enable lazy inode table zeroing.
 332 .TP
 333 .B lazy_journal_init\fR[\fB= \fI<0 to disable, 1 to enable>\fR]
 334 If enabled, the journal inode will not be fully zeroed out by
 335 .BR mke2fs .
 336 This speeds up filesystem initialization noticeably, but carries some
 337 small risk if the system crashes before the journal has been overwritten
 338 entirely one time.  If the option value is omitted, it defaults to 1 to
 339 enable lazy journal inode zeroing.
 340 .TP
 341 .B no_copy_xattrs
 342 Normally
 343 .B mke2fs
 344 will copy the extended attributes of the files in the directory
 345 hierarchy specified via the (optional)
 346 .B \-d
 347 option.  This will disable the copy and leaves the files in the newly
 348 created file system without any extended attributes.
 349 .TP
 350 .BI num_backup_sb= <0|1|2>
 351 If the
 352 .B sparse_super2
 353 file system feature is enabled this option controls whether there will
 354 be 0, 1, or 2 backup superblocks created in the file system.
 355 .TP
 356 .B packed_meta_blocks\fR[\fB= \fI<0 to disable, 1 to enable>\fR]
 357 Place the allocation bitmaps and the inode table at the beginning of the
 358 disk.  This option requires that the flex_bg file system feature to be
 359 enabled in order for it to have effect, and will also create the journal
 360 at the beginning of the file system.  This option is useful for flash
 361 devices that use SLC flash at the beginning of the disk.
 362 It also maximizes the range of contiguous data blocks, which
 363 can be useful for certain specialized use cases, such as supported
 364 Shingled Drives.
 365 .TP
 366 .BI root_owner [=uid:gid]
 367 Specify the numeric user and group ID of the root directory.  If no UID:GID
 368 is specified, use the user and group ID of the user running \fBmke2fs\fR.
 369 In \fBmke2fs\fR 1.42 and earlier the UID and GID of the root directory were
 370 set by default to the UID and GID of the user running the mke2fs command.
 371 The \fBroot_owner=\fR option allows explicitly specifying these values,
 372 and avoid side-effects for users that do not expect the contents of the
 373 filesystem to change based on the user running \fBmke2fs\fR.
 374 .TP
 375 .B test_fs
 376 Set a flag in the filesystem superblock indicating that it may be
 377 mounted using experimental kernel code, such as the ext4dev filesystem.
 378 .TP
 379 .B discard
 380 Attempt to discard blocks at mkfs time (discarding blocks initially is useful
 381 on solid state devices and sparse / thin-provisioned storage). When the device
 382 advertises that discard also zeroes data (any subsequent read after the discard
 383 and before write returns zero), then mark all not-yet-zeroed inode tables as
 384 zeroed. This significantly speeds up filesystem initialization. This is set
 385 as default.
 386 .TP
 387 .B nodiscard
 388 Do not attempt to discard blocks at mkfs time.
 389 .TP
 390 .B quotatype
 391 Specify the which  quota types (usrquota, grpquota, prjquota) which
 392 should be enabled in the created file system.  The argument of this
 393 extended option should be a colon separated list.  This option has
 394 effect only if the
 395 .B quota
 396 feature is set.   The default quota types to be initialized if this
 397 option is not specified is both user and group quotas.  If the project
 398 feature is enabled that project quotas will be initialized as well.
 399 .RE
 400 .TP
 401 .B \-F
 402 Force
 403 .B mke2fs
 404 to create a filesystem, even if the specified device is not a partition
 405 on a block special device, or if other parameters do not make sense.
 406 In order to force
 407 .B mke2fs
 408 to create a filesystem even if the filesystem appears to be in use
 409 or is mounted (a truly dangerous thing to do), this option must be
 410 specified twice.
 411 .TP
 412 .BI \-g " blocks-per-group"
 413 Specify the number of blocks in a block group.  There is generally no
 414 reason for the user to ever set this parameter, as the default is optimal
 415 for the filesystem.  (For administrators who are creating
 416 filesystems on RAID arrays, it is preferable to use the
 417 .I stride
 418 RAID parameter as part of the
 419 .B \-E
 420 option rather than manipulating the number of blocks per group.)
 421 This option is generally used by developers who
 422 are developing test cases.
 423 .IP
 424 If the bigalloc feature is enabled, the
 425 .B \-g
 426 option will specify the number of clusters in a block group.
 427 .TP
 428 .BI \-G " number-of-groups"
 429 Specify the number of block groups that will be packed together to
 430 create a larger virtual block group (or "flex_bg group") in an
 431 ext4 filesystem.  This improves meta-data locality and performance
 432 on meta-data heavy workloads.  The number of groups must be a power
 433 of 2 and may only be specified if the
 434 .B flex_bg
 435 filesystem feature is enabled.
 436 .TP
 437 .BI \-i " bytes-per-inode"
 438 Specify the bytes/inode ratio.
 439 .B mke2fs
 440 creates an inode for every
 441 .I bytes-per-inode
 442 bytes of space on the disk.  The larger the
 443 .I bytes-per-inode
 444 ratio, the fewer inodes will be created.  This value generally shouldn't
 445 be smaller than the blocksize of the filesystem, since in that case more
 446 inodes would be made than can ever be used.  Be warned that it is not
 447 possible to change this ratio on a filesystem after it is created, so be
 448 careful deciding the correct value for this parameter.  Note that resizing
 449 a filesystem changes the number of inodes to maintain this ratio.
 450 .TP
 451 .BI \-I " inode-size"
 452 Specify the size of each inode in bytes.
 453 The
 454 .I inode-size
 455 value must be a power of 2 larger or equal to 128.  The larger the
 456 .I inode-size
 457 the more space the inode table will consume, and this reduces the usable
 458 space in the filesystem and can also negatively impact performance.
 459 It is not
 460 possible to change this value after the filesystem is created.
 461 .IP
 462 In kernels after 2.6.10 and some
 463 earlier vendor kernels it is possible to utilize inodes larger than
 464 128 bytes to store
 465 extended attributes for improved performance.
 466 Extended attributes
 467 stored in large inodes are not visible with older kernels, and such
 468 filesystems will not be mountable with 2.4 kernels at all.
 469 .IP
 470 The default inode size is controlled by the
 471 .BR mke2fs.conf (5)
 472 file.  In the
 473 .B mke2fs.conf
 474 file shipped with e2fsprogs, the default inode size is 256 bytes for
 475 most file systems, except for small file systems where the inode size
 476 will be 128 bytes.
 477 .TP
 478 .B \-j
 479 Create the filesystem with an ext3 journal.  If the
 480 .B \-J
 481 option is not specified, the default journal parameters will be used to
 482 create an appropriately sized journal (given the size of the filesystem)
 483 stored within the filesystem.  Note that you must be using a kernel
 484 which has ext3 support in order to actually make use of the journal.
 485 .TP
 486 .BI \-J " journal-options"
 487 Create the ext3 journal using options specified on the command-line.
 488 Journal options are comma
 489 separated, and may take an argument using the equals ('=')  sign.
 490 The following journal options are supported:
 491 .RS 1.2i
 492 .TP
 493 .BI size= journal-size
 494 Create an internal journal (i.e., stored inside the filesystem) of size
 495 .I journal-size
 496 megabytes.
 497 The size of the journal must be at least 1024 filesystem blocks
 498 (i.e., 1MB if using 1k blocks, 4MB if using 4k blocks, etc.)
 499 and may be no more than 10,240,000 filesystem blocks or half the total
 500 file system size (whichever is smaller)
 501 .TP
 502 .BI location =journal-location
 503 Specify the location of the journal.  The argument
 504 .I journal-location
 505 can either be specified as a block number, or if the number has a units
 506 suffix (e.g., 'M', 'G', etc.) interpret it as the offset from the
 507 beginning of the file system.
 508 @JDEV@.TP
 509 @JDEV@.BI device= external-journal
 510 @JDEV@Attach the filesystem to the journal block device located on
 511 @JDEV@.IR external-journal .
 512 @JDEV@The external
 513 @JDEV@journal must already have been created using the command
 514 @JDEV@.IP
 515 @JDEV@.B mke2fs -O journal_dev
 516 @JDEV@.I external-journal
 517 @JDEV@.IP
 518 @JDEV@Note that
 519 @JDEV@.I external-journal
 520 @JDEV@must have been created with the
 521 @JDEV@same block size as the new filesystem.
 522 @JDEV@In addition, while there is support for attaching
 523 @JDEV@multiple filesystems to a single external journal,
 524 @JDEV@the Linux kernel and
 525 @JDEV@.BR e2fsck (8)
 526 @JDEV@do not currently support shared external journals yet.
 527 @JDEV@.IP
 528 @JDEV@Instead of specifying a device name directly,
 529 @JDEV@.I external-journal
 530 @JDEV@can also be specified by either
 531 @JDEV@.BI LABEL= label
 532 @JDEV@or
 533 @JDEV@.BI UUID= UUID
 534 @JDEV@to locate the external journal by either the volume label or UUID
 535 @JDEV@stored in the ext2 superblock at the start of the journal.  Use
 536 @JDEV@.BR dumpe2fs (8)
 537 @JDEV@to display a journal device's volume label and UUID.  See also the
 538 @JDEV@.B -L
 539 @JDEV@option of
 540 @JDEV@.BR tune2fs (8).
 541 .RE
 542 @JDEV@.IP
 543 @JDEV@Only one of the
 544 @JDEV@.BR size " or " device
 545 @JDEV@options can be given for a filesystem.
 546 .TP
 547 .BI \-l " filename"
 548 Read the bad blocks list from
 549 .IR filename .
 550 Note that the block numbers in the bad block list must be generated
 551 using the same block size as used by
 552 .BR mke2fs .
 553 As a result, the
 554 .B \-c
 555 option to
 556 .B mke2fs
 557 is a much simpler and less error-prone method of checking a disk for bad
 558 blocks before formatting it, as
 559 .B mke2fs
 560 will automatically pass the correct parameters to the
 561 .B badblocks
 562 program.
 563 .TP
 564 .BI \-L " new-volume-label"
 565 Set the volume label for the filesystem to
 566 .IR new-volume-label .
 567 The maximum length of the
 568 volume label is 16 bytes.
 569 .TP
 570 .BI \-m " reserved-blocks-percentage"
 571 Specify the percentage of the filesystem blocks reserved for
 572 the super-user.  This avoids fragmentation, and allows root-owned
 573 daemons, such as
 574 .BR syslogd (8),
 575 to continue to function correctly after non-privileged processes are
 576 prevented from writing to the filesystem.  The default percentage
 577 is 5%.
 578 .TP
 579 .BI \-M " last-mounted-directory"
 580 Set the last mounted directory for the filesystem.  This might be useful
 581 for the sake of utilities that key off of the last mounted directory to
 582 determine where the filesystem should be mounted.
 583 .TP
 584 .B \-n
 585 Causes
 586 .B mke2fs
 587 to not actually create a filesystem, but display what it
 588 would do if it were to create a filesystem.  This can be used to
 589 determine the location of the backup superblocks for a particular
 590 filesystem, so long as the
 591 .B mke2fs
 592 parameters that were passed when the
 593 filesystem was originally created are used again.  (With the
 594 .B \-n
 595 option added, of course!)
 596 .TP
 597 .BI \-N " number-of-inodes"
 598 Overrides the default calculation of the number of inodes that should be
 599 reserved for the filesystem (which is based on the number of blocks and
 600 the
 601 .I bytes-per-inode
 602 ratio).  This allows the user to specify the number
 603 of desired inodes directly.
 604 .TP
 605 .BI \-o " creator-os"
 606 Overrides the default value of the "creator operating system" field of the
 607 filesystem.  The creator field is set by default to the name of the OS the
 608 .B mke2fs
 609 executable was compiled for.
 610 .TP
 611 .B "\-O \fR[^]\fIfeature\fR[,...]"
 612 Create a filesystem with the given features (filesystem options),
 613 overriding the default filesystem options.  The features that are
 614 enabled by default are specified by the
 615 .I base_features
 616 relation, either in the
 617 .I [defaults]
 618 section in the
 619 .B /etc/mke2fs.conf
 620 configuration file,
 621 or in the
 622 .I [fs_types]
 623 subsections for the usage types as specified by the
 624 .B \-T
 625 option, further modified by the
 626 .I features
 627 relation found in the
 628 .I [fs_types]
 629 subsections for the filesystem and usage types.  See the
 630 .BR mke2fs.conf (5)
 631 manual page for more details.
 632 The filesystem type-specific configuration setting found in the
 633 .I [fs_types]
 634 section will override the global default found in
 635 .IR [defaults] .
 636 .sp
 637 The filesystem feature set will be further edited
 638 using either the feature set specified by this option,
 639 or if this option is not given, by the
 640 .I default_features
 641 relation for the filesystem type being created, or in the
 642 .I [defaults]
 643 section of the configuration file.
 644 .sp
 645 The filesystem feature set is comprised of a list of features, separated
 646 by commas, that are to be enabled.  To disable a feature, simply
 647 prefix the feature name with a caret ('^') character.
 648 Features with dependencies will not be removed successfully.
 649 The pseudo-filesystem feature "none" will clear all filesystem features.
 650 .TP
 651 For more information about the features which can be set, please see
 652 the manual page
 653 .BR ext4 (5).
 654 .TP
 655 .B \-q
 656 Quiet execution.  Useful if
 657 .B mke2fs
 658 is run in a script.
 659 .TP
 660 .BI \-r " revision"
 661 Set the filesystem revision for the new filesystem.  Note that 1.2
 662 kernels only support revision 0 filesystems.  The default is to
 663 create revision 1 filesystems.
 664 .TP
 665 .B \-S
 666 Write superblock and group descriptors only.  This is an extreme
 667 measure to be taken only in the very unlikely case that all of
 668 the superblock and backup superblocks are corrupted, and a last-ditch
 669 recovery method is desired by experienced users.  It causes
 670 .B mke2fs
 671 to reinitialize the superblock and group descriptors, while not
 672 touching the inode table and the block and inode bitmaps.  The
 673 .B e2fsck
 674 program should be run immediately after this option is used, and there
 675 is no guarantee that any data will be salvageable.  Due to the wide
 676 variety of possible options to
 677 .B mke2fs
 678 that affect the on-disk layout, it is critical to specify exactly
 679 the same format options, such as blocksize, fs-type, feature flags, and
 680 other tunables when using this option, or the filesystem will be further
 681 corrupted.  In some cases, such as filesystems that have been resized,
 682 or have had features enabled after format time, it is impossible to
 683 overwrite all of the superblocks correctly, and at least some filesystem
 684 corruption will occur.  It is best to run this on a full copy of the
 685 filesystem so other options can be tried if this doesn't work.
 686 .\" .TP
 687 .\" .BI \-t " test"
 688 .\" Check the device for bad blocks before creating the file system
 689 .\" using the specified test.
 690 .TP
 691 .BI \-t " fs-type"
 692 Specify the filesystem type (i.e., ext2, ext3, ext4, etc.) that is
 693 to be created.
 694 If this option is not specified,
 695 .B mke2fs
 696 will pick a default either via how
 697 the command was run (for example, using a name of the form mkfs.ext2,
 698 mkfs.ext3, etc.) or via a default as defined by the
 699 .B /etc/mke2fs.conf
 700 file.   This option controls which filesystem options are used by
 701 default, based on the
 702 .B fstypes
 703 configuration stanza in
 704 .BR /etc/mke2fs.conf .
 705 .sp
 706 If the
 707 .B \-O
 708 option is used to explicitly add or remove filesystem options that
 709 should be set in the newly created filesystem, the
 710 resulting filesystem may not be supported by the requested
 711 .IR fs-type .
 712 (e.g., "\fBmke2fs \-t ext3 \-O extent /dev/sdXX\fR" will create a
 713 filesystem that is not supported by the ext3 implementation as found in
 714 the Linux kernel; and "\fBmke2fs \-t ext3 \-O ^has_journal /dev/hdXX\fR"
 715 will create a filesystem that does not have a journal and hence will not
 716 be supported by the ext3 filesystem code in the Linux kernel.)
 717 .TP
 718 .BI \-T " usage-type[,...]"
 719 Specify how the filesystem is going to be used, so that
 720 .B mke2fs
 721 can choose optimal filesystem parameters for that use.  The usage
 722 types that are supported are defined in the configuration file
 723 .BR /etc/mke2fs.conf .
 724 The user may specify one or more usage types
 725 using a comma separated list.
 726 .sp
 727 If this option is is not specified,
 728 .B mke2fs
 729 will pick a single default usage type based on the size of the filesystem to
 730 be created.  If the filesystem size is less than 3 megabytes,
 731 .B mke2fs
 732 will use the filesystem type
 733 .IR floppy .
 734 If the filesystem size is greater than or equal to 3 but less than
 735 512 megabytes,
 736 .BR mke2fs (8)
 737 will use the filesystem type
 738 .IR small .
 739 If the filesystem size is greater than or equal to 4 terabytes but less than
 740 16 terabytes,
 741 .BR mke2fs (8)
 742 will use the filesystem type
 743 .IR big .
 744 If the filesystem size is greater than or equal to 16 terabytes,
 745 .BR mke2fs (8)
 746 will use the filesystem type
 747 .IR huge .
 748 Otherwise,
 749 .BR mke2fs (8)
 750 will use the default filesystem type
 751 .IR default .
 752 .TP
 753 .BI \-U " UUID"
 754 Set the universally unique identifier (UUID) of the filesystem to
 755 .IR UUID .
 756 The format of the UUID is a series of hex digits separated by hyphens,
 757 like this:
 758 "c1b9d5a2-f162-11cf-9ece-0020afc76f16".
 759 The
 760 .I UUID
 761 parameter may also be one of the following:
 762 .RS 1.2i
 763 .TP
 764 .I clear
 765 clear the filesystem UUID
 766 .TP
 767 .I random
 768 generate a new randomly-generated UUID
 769 .TP
 770 .I time
 771 generate a new time-based UUID
 772 .RE
 773 .TP
 774 .B \-v
 775 Verbose execution.
 776 .TP
 777 .B \-V
 778 Print the version number of
 779 .B mke2fs
 780 and exit.
 781 .TP
 782 .BI \-z " undo_file"
 783 Before overwriting a file system block, write the old contents of the block to
 784 an undo file.  This undo file can be used with e2undo(8) to restore the old
 785 contents of the file system should something go wrong.  If the empty string is
 786 passed as the undo_file argument, the undo file will be written to a file named
 787 mke2fs-\fIdevice\fR.e2undo in the directory specified via the
 788 \fIE2FSPROGS_UNDO_DIR\fR environment variable or the \fIundo_dir\fR directive
 789 in the configuration file.
 790
 791 WARNING: The undo file cannot be used to recover from a power or system crash.
 792 .SH ENVIRONMENT
 793 .TP
 794 .B MKE2FS_SYNC
 795 If set to non-zero integer value, its value is used to determine how often
 796 .BR sync (2)
 797 is called during inode table initialization.
 798 .TP
 799 .B MKE2FS_CONFIG
 800 Determines the location of the configuration file (see
 801 .BR mke2fs.conf (5)).
 802 .TP
 803 .B MKE2FS_FIRST_META_BG
 804 If set to non-zero integer value, its value is used to determine first meta
 805 block group. This is mostly for debugging purposes.
 806 .TP
 807 .B MKE2FS_DEVICE_SECTSIZE
 808 If set to non-zero integer value, its value is used to determine logical
 809 sector size of the
 810 .IR device .
 811 .TP
 812 .B MKE2FS_DEVICE_PHYS_SECTSIZE
 813 If set to non-zero integer value, its value is used to determine physical
 814 sector size of the
 815 .IR device .
 816 .TP
 817 .B MKE2FS_SKIP_CHECK_MSG
 818 If set, do not show the message of filesystem automatic check caused by
 819 mount count or check interval.
 820 .SH AUTHOR
 821 This version of
 822 .B mke2fs
 823 has been written by Theodore Ts'o <tytso@mit.edu>.
 824 .SH AVAILABILITY
 825 .B mke2fs
 826 is part of the e2fsprogs package and is available from
 827 http://e2fsprogs.sourceforge.net.
 828 .SH SEE ALSO
 829 .BR mke2fs.conf (5),
 830 .BR badblocks (8),
 831 .BR dumpe2fs (8),
 832 .BR e2fsck (8),
 833 .BR tune2fs (8),
 834 .BR ext4 (5)