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TUNE2FS(8)		    System Manager's Manual		    TUNE2FS(8)

NAME
       tune2fs	-  adjust  tunable  filesystem	parameters  on second extended
       filesystems

SYNOPSIS
       tune2fs [ -l ] [	-c max-mount-counts ] [	-e errors-behavior ] [ -f ]  [
       -i  interval-between-checks  ]  [  -j ] [ -J journal-options ] [	-m re-
       served-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-direc-
       tory ] [	-O [^]feature[,...]  ] [ -T time-last-checked ]	[  -U  UUID  ]
       device

DESCRIPTION
       tune2fs	adjusts	 tunable  filesystem  parameters on a Linux second ex-
       tended filesystem.

OPTIONS
       -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, ca-
	      bles, 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.	Can be
	      used  in	conjunction 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 er-
	      rors.  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.

       -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 us-
			  ing it.

			  Instead of specifying	a device name directly,	exter-
			  nal-journal can also	be  specified  by  either  LA-
			  BEL=label  or	UUID=UUID to locate the	external jour-
			  nal 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 la-
			  bel 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 overriden  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 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.

		   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 en-
			  abled, 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  en-
			  abled,  all  data is forced directly out to the main
			  file system prior to its metadata being commutted to
			  the journal.

		   journal_data_writeback
			  When	the filesystem is mounted with journalling en-
			  abled, data may be written into the main  filesystem
			  after	 its  metadata has been	commutted to the jour-
			  nal.	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:

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

		   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.

	      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.

	      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>.	 tune2fs  uses
       the ext2fs library written by Theodore Ts'o <tytso@mit.edu>.  This man-
       ual 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 1.32		 November 2002			    TUNE2FS(8)

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | BUGS | AUTHOR | AVAILABILITY | SEE ALSO

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