Provided by: e2fsprogs_1.42.13-1ubuntu1_i386 bug


       tune2fs  -  adjust  tunable  filesystem  parameters  on  ext2/ext3/ext4


       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


       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).


       -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 parameter set by
              the -c option, e2fsck(8) will check the filesystem at  the  next

       -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:

                          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'.

                          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.

                          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

                          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 filesystem.

                          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

       -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 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

       -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.

                          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.

                          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
                          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

              Only one of the size or  device  options  can  be  given  for  a

       -l     List  the  contents  of the filesystem superblock, including the
              current values of the  parameters  that  can  be  set  via  this

       -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

       -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

              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 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.

                          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  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+

                          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+

                          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+

       -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
              system features, please see the man page ext4(5).

              The  following  filesystem  features can be set or cleared using

                          Use hashed b-trees to speed  up  lookups  for  large

                          Allow more than 65000 subdirectories per directory.

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

                          Enable the extended inode fields used by ext4.

                          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 formatted file system with flex_bg

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

                          Support files larger than 2 terabytes in size.

                          Filesystem  can  contain files that are greater than

                          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)

                   quota  Enable internal file system quota inodes.

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

                          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
                          original time, depending on how full the file system

              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:

                          Sets/clears user quota inode in the superblock.

                          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
              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

       -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

       -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.


       We haven't found any bugs yet.  That doesn't mean there aren't any...


       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
       <chk@data-hh.Hanse.DE>.   Time-dependent checking was added by Uwe Ohse


       tune2fs is  part  of  the  e2fsprogs  package  and  is  available  from


       debugfs(8), dumpe2fs(8), e2fsck(8), mke2fs(8), ext4(5)