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TUNE2FS(8)							    TUNE2FS(8)



NAME
       tune2fs - adjust tunable filesystem parameters on ext2/ext3 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 ] [ -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 filesystems.

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.

       -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  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 post-
	      fix or d result in days, m in months, and w in 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	 to go unnoticed until they cause 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.

       -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 reserved filesystem blocks.

       -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 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.

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

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

	      After  setting  or clearing sparse_super and filetype 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 administrator run e2fsck(8) if neces-
	      sary.  After setting the dir_index feature, e2fsck -D can be run
	      to convert existing directories to the hashed B-tree format.

	      Warning: Linux kernels before 2.0.39 and many 2.1 series kernels
	      do  not  support the filesystems that use any of these features.
	      Enabling certain filesystem features may prevent the  filesystem
	      from  being  mounted  by kernels which do not support those fea-
	      tures.

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

       -s [0|1]
	      Turn the sparse super feature off or on.	Turning	 this  feature
	      on  saves	 space on really big filesystems.  This is the same as
	      using the -O sparse_super option.

	      Warning: Linux kernels before 2.0.39 do not  support  this  fea-
	      ture.   Neither  do all Linux 2.1 kernels; please don't use this
	      unless you know what you're doing!  You need to run e2fsck(8) on
	      the  filesystem  after  changing this feature in order to have a
	      valid filesystem.

       -T time-last-checked
	      Set the time the filesystem was last checked using e2fsck.  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[[HHMM]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
       dumpe2fs(8), e2fsck(8), mke2fs(8)



E2fsprogs version 1.39		   May 2006			    TUNE2FS(8)
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