TUNE2FS(8)                  System Manager's Manual                 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  num-
              ber  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 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 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
                          feature 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
                          performance.   It  may also be used by block alloca-
                          tor.

                   stripe_width=stripe-width
                          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.

                   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
                          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.

                   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
                          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 jour-
              nal  (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  corrup-
              tion.

       -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  suf-
              fix  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-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) 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  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.

              If this option is used to create a journal on a mounted filesys-
              tem, 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  invisi-
              ble, 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.

                   location=journal-location
                          Specify the location of the journal.   The  argument
                          journal-location  can either be specified as a block
                          number, or if the number has a units  suffix  (e.g.,
                          'M',  'G', etc.) interpret it as the offset from the
                          beginning of the file system.

                   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
                          journal, the Linux kernel and e2fsck(8) do not  cur-
                          rently support shared external journals yet.

                          Instead of specifying a device name directly, exter-
                          nal-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  pro-
              gram.

       -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 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 filesys-
              tem  fragmentation,  and  to  allow system daemons, such as sys-
              logd(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 filesys-
              tem.   Default  mount options can be overridden 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  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 direc-
                          tory 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 interop-
                          erability  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 filesys-
                          tem 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 opera-
                          tions 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  overwrit-
                          ing parts of the inode table or block group descrip-
                          tors.  This comes at the cost  of  increased  memory
                          and  CPU  overhead, so it is enabled only for debug-
                          ging purposes.  (This option is currently only  sup-
                          ported  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-provi-
                          sioned 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  sup-
                          ported  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  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.  For a detailed description of the file  sys-
              tem features, please see the man page ext4(5).

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

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

                   dir_nlink
                          Allow more than 65000 subdirectories per directory.

                   extent Enable the use of extent trees to store the location
                          of data blocks in inodes.

                   extra_isize
                          Enable the extended inode fields used by ext4.

                   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.

                   huge_file
                          Support files larger than 2 terabytes in size.

                   large_file
                          Filesystem  can  contain files that are greater than
                          2GB.

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

                   mmp    Enable or disable multiple  mount  protection  (MMP)
                          feature.

                   quota  Enable internal file system quota inodes.

                   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  lazily, and to 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 origi-
                          nal 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 adminis-
              trator 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) 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  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[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 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>.  It is cur-
       rently 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>.

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), ext4(5)

E2fsprogs version 1.42.13          May 2015                         TUNE2FS(8)