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TUNE2FS(8)							    TUNE2FS(8)

       tune2fs	-  adjust  tunable  filesystem	parameters  on	ext2/ext3/ext4

       tune2fs [ -l ] [ -c max-mount-counts ] [ -e errors-behavior ] [ -f ]  [
       -i  interval-between-checks  ]  [  -j  ]	 [  -J	journal-options ] [ -m
       reserved-blocks-percentage  ]  [	 -o  [^]mount-options[,...]   ]	 [  -r
       reserved-blocks-count ] [ -s sparse-super-flag ] [ -u user ] [ -g group
       ] [ -C mount-count ] [ -E extended-options ] [ -L volume-name  ]	 [  -M
       last-mounted-directory  ] [ -O [^]feature[,...]	] [ -Q quota-options ]
       [ -T time-last-checked ] [ -U UUID ] device

       tune2fs allows the  system  administrator  to  adjust  various  tunable
       filesystem  parameters  on  Linux ext2, ext3, or ext4 filesystems.  The
       current values of these options can be displayed by using the -l option
       to tune2fs(8) program, or by using the dumpe2fs(8) program.

       The  device  specifier can either be a filename (i.e., /dev/sda1), or a
       LABEL or UUID specifier: "LABEL=volume-name"  or	 "UUID=uuid".	(i.e.,
       LABEL=home or UUID=e40486c6-84d5-4f2f-b99c-032281799c9d).

       -c max-mount-counts
	      Adjust  the  number of mounts after which the filesystem will be
	      checked by e2fsck(8).  If max-mount-counts is 0 or -1, the  num‐
	      ber  of  times  the filesystem is mounted will be disregarded by
	      e2fsck(8) and the kernel.

	      Staggering the mount-counts at which  filesystems	 are  forcibly
	      checked  will  avoid  all	 filesystems being checked at one time
	      when using journaled filesystems.

	      You should  strongly  consider  the  consequences	 of  disabling
	      mount-count-dependent   checking	entirely.   Bad	 disk  drives,
	      cables, memory, and kernel bugs could all corrupt	 a  filesystem
	      without  marking	the  filesystem dirty or in error.  If you are
	      using journaling on your filesystem, your filesystem will	 never
	      be marked dirty, so it will not normally be checked.  A filesys‐
	      tem error detected by the kernel will still force an fsck on the
	      next reboot, but it may already be too late to prevent data loss
	      at that point.

	      See also the -i option for time-dependent checking.

       -C mount-count
	      Set the number of times the filesystem has been mounted.	If set
	      to  a  greater  value than the max-mount-counts parameter set by
	      the -c option, e2fsck(8) will check the filesystem at  the  next

       -e error-behavior
	      Change the behavior of the kernel code when errors are detected.
	      In all cases, a filesystem error will cause e2fsck(8)  to	 check
	      the  filesystem  on the next boot.  error-behavior can be one of
	      the following:

		   continue    Continue normal execution.

		   remount-ro  Remount filesystem read-only.

		   panic       Cause a kernel panic.

       -E extended-options
	      Set extended options for the filesystem.	Extended  options  are
	      comma separated, and may take an argument using the equals ('=')
	      sign.  The following extended options are supported:

			  Reset the MMP block  (if  any)  back	to  the	 clean
			  state.  Use only if absolutely certain the device is
			  not currently mounted	 or  being  fscked,  or	 major
			  filesystem corruption can result.  Needs '-f'.

			  Adjust  the  initial MMP update interval to interval
			  seconds.  Specifying an interval of 0 means  to  use
			  the  default	interval.  The specified interval must
			  be less than 300 seconds.   Requires	that  the  mmp
			  feature be enabled.

			  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 next
			  disk. This mostly affects  placement	of  filesystem
			  metadata  like  bitmaps  at  mke2fs(2) time to avoid
			  placing them on a single disk, which	can  hurt  the
			  performance.	 It  may also be used by block alloca‐

			  Configure the	 filesystem  for  a  RAID  array  with
			  stripe-width	filesystem  blocks per stripe. This is
			  typically be stride-size * N, where N is the	number
			  of  data  disks in the RAID (e.g. RAID 5 N+1, RAID 6
			  N+2).	 This allows the block	allocator  to  prevent
			  read-modify-write  of the parity in a RAID stripe if
			  possible when the data is written.

			  Set the default hash algorithm used for  filesystems
			  with	hashed	b-tree	directories.  Valid algorithms
			  accepted are: legacy, half_md4, and tea.

			  Set a set of default mount  options  which  will  be
			  used	when  the  file system is mounted.  Unlike the
			  bitmask-based default mount  options	which  can  be
			  specified with the -o option, mount_option_string is
			  an arbitrary string with  a  maximum	length	of  63
			  bytes, which is stored in the superblock.

			  The  ext4  file  system  driver will first apply the
			  bitmask-based default options, and  then  parse  the
			  mount_option_string,	 before	  parsing   the	 mount
			  options passed from the mount(8) program.

			  This superblock setting is only honored  in  2.6.35+
			  kernels;  and	 not  at all by the ext2 and ext3 file
			  system drivers.

			  Set a flag in the filesystem	superblock  indicating
			  that	it  may	 be  mounted using experimental kernel
			  code, such as the ext4dev filesystem.

			  Clear the test_fs flag,  indicating  the  filesystem
			  should   only	  be  mounted  using  production-level
			  filesystem code.

       -f     Force the tune2fs operation to complete  even  in	 the  face  of
	      errors.	This  option  is  useful when removing the has_journal
	      filesystem feature from a filesystem which has an external jour‐
	      nal  (or	is  corrupted such that it appears to have an external
	      journal), but that external journal is not available.

	      WARNING: Removing an external journal from  a  filesystem	 which
	      was  not	cleanly unmounted without first replaying the external
	      journal can result in severe data loss  and  filesystem  corrup‐

       -g group
	      Set the group which can use the reserved filesystem blocks.  The
	      group parameter can be a numerical gid or a group	 name.	 If  a
	      group  name  is given, it is converted to a numerical gid before
	      it is stored in the superblock.

       -i  interval-between-checks[d|m|w]
	      Adjust the maximal time between two filesystem checks.  No  suf‐
	      fix  or  d  will interpret the number interval-between-checks as
	      days, m as months, and w as weeks.  A value of zero will disable
	      the time-dependent checking.

	      It  is  strongly	recommended that either -c (mount-count-depen‐
	      dent) or -i (time-dependent) checking be enabled to force	 peri‐
	      odic  full  e2fsck(8) checking of the filesystem.	 Failure to do
	      so may lead to filesystem corruption (due to bad disks,  cables,
	      memory, or kernel bugs) going unnoticed, ultimately resulting in
	      data loss or corruption.

       -j     Add an ext3 journal to the filesystem.  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  filesys‐
	      tem)  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.

	      If this option is used to create a journal on a mounted filesys‐
	      tem, an immutable file, .journal, will be created	 in  the  top-
	      level directory of the filesystem, as it is the only safe way to
	      create the journal inode while the filesystem is mounted.	 While
	      the  ext3	 journal  is  visible, it is not safe to delete it, or
	      modify it while the filesystem is mounted; for this  reason  the
	      file is marked immutable.	 While checking unmounted filesystems,
	      e2fsck(8) will automatically move .journal files to the  invisi‐
	      ble, reserved journal inode.  For all filesystems except for the
	      root filesystem,	this should happen automatically and naturally
	      during  the  next	 reboot	 cycle.	  Since the root filesystem is
	      mounted read-only, e2fsck(8) must be run from a rescue floppy in
	      order to effect this transition.

	      On  some distributions, such as Debian, if an initial ramdisk is
	      used, the initrd scripts will automatically convert an ext2 root
	      filesystem  to  ext3  if	the /etc/fstab file specifies the ext3
	      filesystem for the root filesystem in order to  avoid  requiring
	      the  use	of  a rescue floppy to add an ext3 journal to the root

       -J journal-options
	      Override the default ext3 journal	 parameters.  Journal  options
	      are  comma  separated, and may take an argument using the equals
	      ('=')  sign.  The following journal options are supported:

			  Create a journal stored in 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.
			  There must be enough free space in the filesystem to
			  create a journal of that size.

			  Attach the filesystem to the	journal	 block	device
			  located  on  external-journal.  The external journal
			  must have been already created using the command

			  mke2fs -O journal_dev external-journal

			  Note that external-journal must  be  formatted  with
			  the  same  block  size  as filesystems which will be
			  using it.  In addition, while there is  support  for
			  attaching  multiple filesystems to a single external
			  journal, the Linux kernel and e2fsck(8) do not  cur‐
			  rently support shared external journals yet.

			  Instead of specifying a device name directly, exter‐
			  nal-journal  can  also  be   specified   by	either
			  LABEL=label  or  UUID=UUID  to  locate  the external
			  journal by either the volume label or UUID stored in
			  the  ext2  superblock	 at  the start of the journal.
			  Use dumpe2fs(8) to display a journal device's volume
			  label	  and	UUID.	See  also  the	-L  option  of

	      Only one of the size or  device  options	can  be	 given	for  a

       -l     List  the	 contents  of the filesystem superblock, including the
	      current values of the parameters that can be set via  this  pro‐

       -L volume-label
	      Set  the volume label of the filesystem.	Ext2 filesystem labels
	      can be at most 16 characters long;  if  volume-label  is	longer
	      than  16	characters, tune2fs will truncate it and print a warn‐
	      ing.  The volume label can be used  by  mount(8),	 fsck(8),  and
	      /etc/fstab(5)  (and  possibly  others)  by specifying LABEL=vol‐
	      ume_label instead of a block special device name like /dev/hda5.

       -m reserved-blocks-percentage
	      Set the percentage of the filesystem which may only be allocated
	      by  privileged  processes.   Reserving some number of filesystem
	      blocks for use by privileged processes is done to avoid filesys‐
	      tem  fragmentation,  and	to  allow system daemons, such as sys‐
	      logd(8), to continue to function correctly after	non-privileged
	      processes	 are  prevented	 from writing to the filesystem.  Nor‐
	      mally, the default percentage of reserved blocks is 5%.

       -M last-mounted-directory
	      Set the last-mounted directory for the filesystem.

       -o [^]mount-option[,...]
	      Set or clear the indicated default mount options in the filesys‐
	      tem.   Default  mount options can be overridden by mount options
	      specified either in /etc/fstab(5) or on the command  line	 argu‐
	      ments  to mount(8).  Older kernels may not support this feature;
	      in particular, kernels which predate  2.4.20  will  almost  cer‐
	      tainly ignore the default mount options field in the superblock.

	      More  than  one mount option can be cleared or set by separating
	      features with commas.  Mount options prefixed with a caret char‐
	      acter  ('^')  will  be  cleared  in the filesystem's superblock;
	      mount options without a prefix character or prefixed with a plus
	      character ('+') will be added to the filesystem.

	      The following mount options can be set or cleared using tune2fs:

		   debug  Enable debugging code for this filesystem.

			  Emulate  BSD	behavior when creating new files: they
			  will take the group-id of  the  directory  in	 which
			  they	were  created.	The standard System V behavior
			  is the default, where newly created  files  take  on
			  the  fsgid of the current process, unless the direc‐
			  tory has the setgid bit set, in which case it	 takes
			  the gid from the parent directory, and also gets the
			  setgid bit set if it is a directory itself.

			  Enable user-specified extended attributes.

		   acl	  Enable Posix Access Control Lists.

		   uid16  Disables 32-bit UIDs and GIDs.  This is for interop‐
			  erability  with  older  kernels which only store and
			  expect 16-bit values.

			  When the  filesystem	is  mounted  with  journalling
			  enabled,  all	 data (not just metadata) is committed
			  into the journal prior to  being  written  into  the
			  main filesystem.

			  When	the  filesystem	 is  mounted  with journalling
			  enabled, all data is forced directly out to the main
			  file system prior to its metadata being committed to
			  the journal.

			  When the  filesystem	is  mounted  with  journalling
			  enabled,  data may be written into the main filesys‐
			  tem after its metadata has  been  committed  to  the
			  journal.   This may increase throughput, however, it
			  may allow old data to appear in files after a	 crash
			  and journal recovery.

			  The  file system will be mounted with barrier opera‐
			  tions in the journal disabled.  (This option is cur‐
			  rently only supported by the ext4 file system driver
			  in 2.6.35+ kernels.)

			  The  file  system   will   be	  mounted   with   the
			  block_validity  option  enabled,  which causes extra
			  checks to be performed after reading or writing from
			  the  file  system.  This prevents corrupted metadata
			  blocks from causing file system damage by  overwrit‐
			  ing parts of the inode table or block group descrip‐
			  tors.	 This comes at the cost	 of  increased	memory
			  and  CPU  overhead, so it is enabled only for debug‐
			  ging purposes.  (This option is currently only  sup‐
			  ported  by  the  ext4	 file system driver in 2.6.35+

			  The file system will be  mounted  with  the  discard
			  mount	 option.   This	 will  cause  the  file system
			  driver to attempt to use the trim/discard feature of
			  some	storage devices (such as SSD's and thin-provi‐
			  sioned drives available in some  enterprise  storage
			  arrays)  to  inform  the  storage device that blocks
			  belonging to deleted files can be reused  for	 other
			  purposes.   (This option is currently only supported
			  by the ext4 file system driver in 2.6.35+ kernels.)

			  The file system will be mounted with the  nodelalloc
			  mount option.	 This will disable the delayed alloca‐
			  tion feature.	 (This option is currently  only  sup‐
			  ported  by  the  ext4	 file system driver in 2.6.35+

       -O [^]feature[,...]
	      Set or clear the indicated filesystem features (options) in  the
	      filesystem.   More than one filesystem feature can be cleared or
	      set by separating features  with	commas.	  Filesystem  features
	      prefixed	with  a	 caret	character ('^') will be cleared in the
	      filesystem's superblock; filesystem features  without  a	prefix
	      character	 or prefixed with a plus character ('+') will be added
	      to the filesystem.  For a detailed description of the file  sys‐
	      tem features, please see the man page ext4(5).

	      The  following  filesystem  features can be set or cleared using

			  Use hashed b-trees to speed  up  lookups  for	 large

			  Allow more than 65000 subdirectories per directory.

		   extent Enable the use of extent trees to store the location
			  of data blocks in inodes.

			  Enable the extended inode fields used by ext4.

			  Store file type information in directory entries.

			  Allow bitmaps and inode tables for a block group  to
			  be  placed  anywhere	on the storage media.  Tune2fs
			  will not reorganize the location of the inode tables
			  and allocation bitmaps, as mke2fs(8) will do when it
			  creates a freshly formatted file system with flex_bg

			  Use  a journal to ensure filesystem consistency even
			  across unclean shutdowns.   Setting  the  filesystem
			  feature is equivalent to using the -j option.

			  Support files larger than 2 terabytes in size.

			  Filesystem  can  contain files that are greater than

			  Reserve space so the block  group  descriptor	 table
			  may  grow  in	 the  future.	Tune2fs	 only supports
			  clearing this filesystem feature.

		   mmp	  Enable or disable multiple  mount  protection	 (MMP)

			  Limit the number of backup superblocks to save space
			  on large filesystems.

			  Allow the kernel to  initialize  bitmaps  and	 inode
			  tables  lazily, and to keep a high watermark for the
			  unused inodes in a filesystem, to  reduce  e2fsck(8)
			  time.	  This	first  e2fsck  run after enabling this
			  feature will take  the  full	time,  but  subsequent
			  e2fsck  runs will take only a fraction of the origi‐
			  nal time, depending on how full the file system is.

	      After setting or clearing sparse_super, uninit_bg, filetype,  or
	      resize_inode  filesystem	features, e2fsck(8) must be run on the
	      filesystem to return  the	 filesystem  to	 a  consistent	state.
	      Tune2fs will print a message requesting that the system adminis‐
	      trator run e2fsck(8) if necessary.  After setting the  dir_index
	      feature, e2fsck -D can be run to convert existing directories to
	      the hashed B-tree format.	 Enabling certain filesystem  features
	      may  prevent  the filesystem from being mounted by kernels which
	      do not support those features.  In particular, the uninit_bg and
	      flex_bg features are only supported by the ext4 filesystem.

       -p mmp_check_interval
	      Set  the	desired MMP check interval in seconds. It is 5 seconds
	      by default.

       -r reserved-blocks-count
	      Set the number of reserved filesystem blocks.

       -Q quota-options
	      Sets 'quota' feature on the superblock and works	on  the	 quota
	      files  for  the  given quota type. Quota options could be one or
	      more of the following:

			  Sets/clears user quota inode in the superblock.

			  Sets/clears group quota inode in the superblock.

       -T time-last-checked
	      Set the time the filesystem was last checked using e2fsck.   The
	      time  is	interpreted  using the current (local) timezone.  This
	      can be useful in scripts which use a Logical Volume  Manager  to
	      make  a  consistent snapshot of a filesystem, and then check the
	      filesystem during off hours to make sure	it  hasn't  been  cor‐
	      rupted  due  to  hardware	 problems, etc.	 If the filesystem was
	      clean, then this option can be used to set the last checked time
	      on  the original filesystem.  The format of time-last-checked is
	      the international date format, with an optional time  specifier,
	      i.e.   YYYYMMDD[HH[MM[SS]]].   The keyword now is also accepted,
	      in which case the last checked time will be set to  the  current

       -u user
	      Set  the	user who can use the reserved filesystem blocks.  user
	      can be a numerical uid or a user name.  If a user name is given,
	      it  is  converted	 to a numerical uid before it is stored in the

       -U UUID
	      Set the universally unique identifier (UUID) of  the  filesystem
	      to UUID.	The format of the UUID is a series of hex digits sepa‐
	      rated	     by		 hyphens,	   like		 this:
	      "c1b9d5a2-f162-11cf-9ece-0020afc76f16".	The UUID parameter may
	      also be one of the following:

		   clear  clear the filesystem UUID

		   random generate a new randomly-generated UUID

		   time	  generate a new time-based UUID

	      The UUID may be used by  mount(8),  fsck(8),  and	 /etc/fstab(5)
	      (and possibly others) by specifying UUID=uuid instead of a block
	      special device name like /dev/hda1.

	      See uuidgen(8) for more information.  If	the  system  does  not
	      have  a  good  random  number  generator	such as /dev/random or
	      /dev/urandom, tune2fs will automatically use a  time-based  UUID
	      instead of a randomly-generated UUID.

       We haven't found any bugs yet.  That doesn't mean there aren't any...

       tune2fs	was  written  by  Remy Card <Remy.Card@linux.org>.  It is cur‐
       rently being maintained by Theodore Ts'o <tytso@alum.mit.edu>.  tune2fs
       uses the ext2fs library written by Theodore Ts'o <tytso@mit.edu>.  This
       manual page was	written	 by  Christian	Kuhtz  <chk@data-hh.Hanse.DE>.
       Time-dependent checking was added by Uwe Ohse <uwe@tirka.gun.de>.

       tune2fs	is  part  of  the  e2fsprogs  package  and  is	available from

       debugfs(8), dumpe2fs(8), e2fsck(8), mke2fs(8), ext4(5)

E2fsprogs version 1.42.9	 December 2013			    TUNE2FS(8)

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