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       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  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.

              Mount-count-dependent checking is disabled by default  to  avoid
              unanticipated long reboots while e2fsck does its work.  However,
              you may wish to 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
              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 alloca-

                          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.

       -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-

       -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.

              There  are pros and cons to disabling these periodic checks; see
              the discussion under the -c (mount-count-dependent check) option
              for details.

       -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
                          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, 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

              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 pro-

       -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%.

              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  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.

                          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.

                          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  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.

                          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.)

                          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.)

                          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+

       -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

                          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

                          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)

                          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  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:

                          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
              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 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.


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


       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>.


       tune2fs is  part  of  the  e2fsprogs  package  and  is  available  from


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

E2fsprogs version 1.42.9 December 2013 TUNE2FS(8)

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