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[,...]  ] [ -Q quota-options ] [ -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 specifier can either be a filename (i.e., /dev/sda1), or a  LABEL  or  UUID  specifier:  "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 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 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 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 param‐
	      eter 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:

		   clear_mmp
			  Reset the MMP block (if any) back to the clean state.  Use only if absolutely certain the device is  not
			  currently mounted or being fscked, or major filesystem corruption can result.  Needs '-f'.

		   mmp_update_interval=interval
			  Adjust  the  initial	MMP update interval to interval seconds.  Specifying an interval of 0 means to use
			  the default interval.  The specified interval must be less than 300 seconds.	Requires that the mmp fea‐
			  ture be enabled.

		   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 per‐
			  formance.  It may also be used by block allocator.

		   stripe_width=stripe-width
			  Configure the filesystem for a RAID array with stripe-width filesystem blocks per stripe. This is  typi‐
			  cally 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.

		   mount_opts=mount_option_string
			  Set a set of default mount options which will be used when the file system is mounted.  Unlike the  bit‐
			  mask-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.

		   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 filesys‐
			  tem 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 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 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 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-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 journal.

	      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 filesys‐
	      tem  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 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 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 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 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	truncate  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  spe‐
	      cial 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 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 feature; 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 commas.  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.

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

		   user_xattr
			  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.

		   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 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.

		   nobarrier
			  The  file  system will be mounted with barrier operations in the journal disabled.  (This option is cur‐
			  rently only supported by the ext4 file system driver in 2.6.35+ kernels.)

		   block_validity
			  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+ kernels.)

		   discard
			  The file system will be mounted 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 storage 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.)

		   nodelalloc
			  The file system will be mounted with the nodelalloc mount option.  This will disable the delayed alloca‐
			  tion	feature.   (This option is currently only supported by the ext4 file system driver in 2.6.35+ ker‐
			  nels.)

       -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.

		   dir_nlink
			  Allow more than 65000 subdirectories per directory.

		   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 formatted 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 clear‐
			  ing this filesystem feature.

		   mmp	  Enable or disable multiple mount protection (MMP) feature.  MMP helps to  protect  the  filesystem  from
			  being multiply mounted and is useful in shared storage environments.

		   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 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.

       -p mmp_check_interval
	      Set the desired MMP check interval in seconds. It is 5 seconds by default.

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

       -Q quota-options
	      Sets 'quota' feature on the superblock and works on the quota files for the given quota type. Quota options could be
	      one or more of the following:

		   [^]usrquota
			  Sets/clears user quota inode in the superblock.

		   [^]grpquota
			  Sets/clears group quota inode in the superblock.

       -T time-last-checked
	      Set the time the filesystem was last checked using e2fsck.  The time is interpreted using the current (local)  time‐
	      zone.   This can be useful in scripts which use a Logical Volume Manager to make a consistent snapshot of a filesys‐
	      tem, 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[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 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  .   It  is  currently  being  maintained	by  Theodore  Ts'o
       .  tune2fs uses the ext2fs library written by Theodore Ts'o	.   This  manual  page  was
       written by Christian Kuhtz .  Time-dependent checking was added by Uwe Ohse .

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 1.42.5				     July 2012							TUNE2FS(8)




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