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TUNE2FS(8)									       TUNE2FS(8)

       tune2fs - adjust tunable filesystem parameters on second extended 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 ] [ -L volume-name ] [ -M last-mounted-directory ] [ -O  [^]feature[,...]	 ]  [  -T
       time-last-checked ] [ -U UUID ] device

       tune2fs adjusts tunable filesystem parameters on a Linux second extended filesystem.

       -c max-mount-counts
	      Adjust the maximal mounts count between two filesystem checks.  If max-mount-counts
	      is 0 then 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.	Can be used  in  conjunc-
	      tion with -c to force an fsck on 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 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 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 postfix or d  result  in
	      days, m in months, and w in weeks.  A value of zero will disable the time-dependent

	      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 to go unnoticed until they cause data loss or cor-

       -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

       -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.

			  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.

       -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 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 filesystem.  Default  mount
	      options  can  be overriden 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 crrent process, unless the directry 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.

			  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
			  commutted to the journal.

			  When	the  filesystem  is mounted with journalling enabled, data may be
			  written into the main filesystem after its metadata has been	commutted
			  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 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:

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

			  Store file type information in directory entries.

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

	      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 necessary.

	      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

       -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 feature.  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 corrupted 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  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>.	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-

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

E2fsprogs version 1.32			  November 2002 			       TUNE2FS(8)
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