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Linux 2.6 - man page for tune2fs (linux section 8)

TUNE2FS(8)									       TUNE2FS(8)

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

       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

       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  dis-
       played 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

       -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 number 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 cor-
	      rupt 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 filesystem 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:

			  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  meta-
			  data	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

			  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 journal (or is corrupted such that it appears to have an external jour-
	      nal), 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 corruption.

       -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 suffix or d will  inter-
	      pret  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-dependent)  or  -i  (time-
	      dependent)  checking  be	enabled  to force periodic 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 filesystem) stored within the  filesystem.   Note	that  you
	      must  be using a kernel which has ext3 support in order to actually make use of the

	      If this option is used to create a journal on a mounted  filesystem,  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 invisible, 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

			  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 jour-
			  nal, the Linux kernel and e2fsck(8) do  not  currently  support  shared
			  external journals yet.

			  Instead of specifying a device name directly, external-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 filesystem.

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

       -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  trun-
	      cate  it	and  print a warning.  The volume label can be used by mount(8), fsck(8),
	      and /etc/fstab(5) (and possibly others) by specifying LABEL=volume_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 pro-
	      cesses.	Reserving some number of filesystem blocks for	use  by  privileged  pro-
	      cesses is done to avoid filesystem fragmentation, and to allow system daemons, such
	      as syslogd(8), to continue to function correctly after non-privileged processes are
	      prevented  from  writing	to  the  filesystem.  Normally, 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 filesystem.  Default  mount
	      options  can be overridden by mount options specified either in /etc/fstab(5) or on
	      the command line arguments to mount(8).  Older kernels may not  support  this  fea-
	      ture;  in particular, kernels which predate 2.4.20 will almost certainly ignore the
	      default mount options field in the superblock.

	      More than one mount option can be cleared or set by separating features  with  com-
	      mas.   Mount  options  prefixed with a caret character ('^') 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	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 directory 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 interoperability 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 filesystem 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 operations in the  journal
			  disabled.   (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 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  overwriting parts of the inode table or block
			  group descriptors.  This comes at the cost of increased memory and  CPU
			  overhead,  so  it is enabled only for debugging purposes.  (This option
			  is currently only supported by the ext4 file system driver  in  2.6.35+

			  The  file  system will be mouinted 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-provisioned
			  drives available in some enterprise storage arrays) to inform the stor-
			  age  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 allocation feature.	(This option is currently
			  only supported by the ext4 file system driver in 2.6.35+ kernels.)

       -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  com-
	      mas.   Filesystem features prefixed with a caret character ('^') will be cleared in
	      the filesystem's superblock; filesystem features without a prefix character or pre-
	      fixed with a plus character ('+') will be added to the filesystem.

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

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

			  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 cre-
			  ates a freshly formated file system with flex_bg enabled.

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

			  Filesystem can contain files that are greater than 2GB.   (Modern  ker-
			  nels set this feature automatically when a file > 2GB is created.)

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

			  Limit the number of backup superblocks to save space on large  filesys-

			  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 filesys-
	      tem to a consistent state.  Tune2fs will print a message requesting that the system
	      administrator 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 Log-
	      ical 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 corrupted due to hard-
	      ware 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  separated	by  hyphens,  like  this:
	      "c1b9d5a2-f162-11cf-9ece-0020afc76f16".  The UUID parameter may also be one of  the

		   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 currently 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 http://e2fsprogs.source-

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

E2fsprogs version 1.41.14		  December 2010 			       TUNE2FS(8)

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