Provided by: e2fsprogs_1.41.9-1ubuntu3_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[,...]   ]  [ -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.


       -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:

                          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  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.

              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
              postfix or d result in days, m in months, and  w  in  weeks.   A
              value of zero will disable the time-dependent checking.

              It   is   strongly  recommended  that  either  -c  (mount-count-
              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.

                          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 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.

       -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

                          Filesystem  can  contain files that are greater than
                          2GB.  (Modern kernels set this feature automatically
                          when a file > 2GB is created.)

                          Use  hashed  b-trees  to  speed  up lookups in large

                          Store file type information in directory entries.

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

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

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

                          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.

       -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

       -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)