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TUNE2FS(8)							    TUNE2FS(8)

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

SYNOPSIS
       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[,...]   ]  [ -T time-last-
       checked ] [ -U UUID ] device

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

OPTIONS
       -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
	      reboot.

       -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:

		   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 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‐
			  tor.

		   stripe_width=stripe-width
			  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.

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

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

		   ^test_fs
			  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‐
	      tion.

       -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
	      filesystem.

       -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:

		   size=journal-size
			  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.

		   device=external-journal
			  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
			  tune2fs(8).

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

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

       -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.

		   bsdgroups
			  Emulate BSD behaviour when creating new files:  they
			  will	take  the  group-id  of the directory in which
			  they were created.  The standard System V  behaviour
			  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.

		   user_xattr
			  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.

		   journal_data
			  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.

		   journal_data_ordered
			  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.

		   journal_data_writeback
			  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.

       -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.

	      The following filesystem features can be set  or	cleared	 using
	      tune2fs:

		   dir_index
			  Use  hashed  b-trees	to  speed  up lookups in large
			  directories.

		   filetype
			  Store file type information in directory entries.

		   flex_bg
			  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 formated file system with  flex_bg
			  enabled.

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

		   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.   Tune2fs	only  supports
			  clearing this filesystem feature.

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

		   uninit_bg
			  Allow the kernel to  initialize  bitmaps  and	 inode
			  tables  and  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 original 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.

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

       -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
	      time.

       -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
	      superblock.

       -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.

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

AUTHOR
       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>.

AVAILABILITY
       tune2fs is  part	 of  the  e2fsprogs  package  and  is  available  from
       http://e2fsprogs.sourceforge.net.

SEE ALSO
       debugfs(8), dumpe2fs(8), e2fsck(8), mke2fs(8)

E2fsprogs version 1.41.12	   May 2010			    TUNE2FS(8)
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