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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 param-
       eters  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.

       -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 filesys-
              tem 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

              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.

       -E extended-options
              Set  extended  options for the filesystem.  Extended options are comma sepa-
              rated, 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 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.

                          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

                          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 journal),  but  that  external  journal  is  not
              available.    If  the  filesystem  appears to require journal replay, the -f
              flag must be specified twice to proceed.

              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) check-
              ing of the filesystem.  Failure to do so may lead to  filesystem  corruption
              (due  to  bad  disks, cables, memory, or kernel bugs) going unnoticed, ulti-
              mately 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
              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 filesystem.

       -J journal-options
              Override the default ext3 journal parameters. Journal options are comma sep-
              arated,  and may take an argument using the equals ('=')  sign.  The follow-
              ing 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 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, 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 special device name like /dev/hda5.

       -m reserved-blocks-percentage
              Set  the  percentage of the filesystem which may only be allocated by privi-
              leged 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.  Nor-
              mally, 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

              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.

                          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 meta-
                          data 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.)

                          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 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.)

                          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 fea-
              tures 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:

                          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 creates 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
                          kernels set this feature automatically when a file > 2GB is cre-

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

                          Limit  the  number  of backup superblocks to save space on large

                          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 fea-
              tures.  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 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[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

              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 AT linux.org>.  It is currently being
       maintained by Theodore Ts'o <tytso AT alum.edu>.  tune2fs uses the ext2fs  library
       written  by  Theodore Ts'o <tytso AT mit.edu>.  This manual page was written by Chris-
       tian Kuhtz <chk AT data-hh.DE>.  Time-dependent checking was added by  Uwe  Ohse
       <uwe AT tirka.de>.

       tune2fs    is   part   of   the   e2fsprogs   package   and   is   available   from

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

E2fsprogs version 1.41.12          May 2010                         TUNE2FS(8)

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