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TUNE2FS(8)                                                          TUNE2FS(8)

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

       tune2fs [ -l ] [ -c max-mount-counts ] [ -e errors-behavior ] [ -f ] [ -i interval-between-checks ] [ -j ] [ -J
       journal-options ] [ -m reserved-blocks-percentage ] [ -o [^]mount-options[,...]  ] [ -r reserved-blocks-count ]
       [ -s sparse-super-flag ] [ -u user ] [ -g group ] [ -C mount-count ] [ -E extended-options ] [ -L volume-name ]
       [ -M last-mounted-directory ] [ -O [^]feature[,...]  ] [ -T time-last-checked ] [ -U UUID ] device

       tune2fs allows the system administrator to adjust various tunable filesystem 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 filesys-
              tem  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 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:

                          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 allocator.

                          Configure  the  filesystem  for a RAID array with stripe-width filesystem blocks per stripe.
                          This is typically be stride-size * N, where N is the number of data disks in the RAID  (e.g.
                          RAID  5  N+1,  RAID 6 N+2).  This allows the block allocator to prevent read-modify-write of
                          the parity in a RAID stripe if possible when the data is written.

                          Set the default hash algorithm used for filesystems with hashed b-tree  directories.   Valid
                          algorithms accepted are: legacy, half_md4, and tea.

                          Set  a  set  of  default  mount  options which will be used when the file system is mounted.
                          Unlike the bitmask-based default mount options which can be specified with  the  -o  option,
                          mount_option_string  is  an  arbitrary  string  with  a maximum length of 63 bytes, which is
                          stored in the superblock.

                          The ext4 file system driver will first apply the bitmask-based  default  options,  and  then
                          parse  the  mount_option_string,  before  parsing the mount options passed from the mount(8)

                          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 corruption.

       -g group
              Set  the group which can use the reserved filesystem blocks.  The group parameter can be a numerical gid
              or a group name.  If a group name is given, it is converted to a numerical gid before it  is  stored  in
              the superblock.

       -i  interval-between-checks[d|m|w]
              Adjust  the maximal time between two filesystem checks.  No suffix or d will interpret the number inter-
              val-between-checks as days, m as months, and w as weeks.  A value of zero will disable  the  time-depen-
              dent 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  parame-
              ters  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  auto-
              matically  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  automati-
              cally  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 argu-
              ment 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 tune2fs(8).

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

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

       -L volume-label
              Set  the  volume  label of the filesystem.  Ext2 filesystem labels can be at most 16 characters long; if
              volume-label is longer than 16 characters, tune2fs will truncate it and print  a  warning.   The  volume
              label can be used by mount(8), fsck(8), and /etc/fstab(5) (and possibly others) by specifying LABEL=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 filesystem fragmenta-
              tion, and to allow system daemons, such as syslogd(8), to continue to function correctly after non-priv-
              ileged  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  over-
              ridden  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 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 pre-
              fixed 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 through-
                          put, 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  cor-
                          rupted metadata blocks from causing file system damage by overwriting parts of the inode ta-
                          ble or block group descriptors.  This comes at the cost of increased memory  and  CPU  over-
                          head,  so  it  is  enabled only for debugging purposes.  (This option is currently only sup-
                          ported by the ext4 file system driver in 2.6.35+ kernels.)

                          The file system will be mouinted with the discard mount option.  This will  cause  the  file
                          system  driver  to  attempt to use the trim/discard feature of some storage devices (such as
                          SSD's and thin-provisioned drives available in some enterprise storage arrays) to inform the
                          storage  device  that  blocks  belonging  to deleted files can be reused for other purposes.
                          (This option is currently only supported by the ext4 file system driver in 2.6.35+ kernels.)

                          The  file  system  will  be mounted with the nodelalloc mount option.  This will disable the
                          delayed allocation feature.  (This option is currently only supported by the ext4 file  sys-
                          tem 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 pre-
              fix character or prefixed with a plus character ('+') will be added to the filesystem.

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

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

                          Store file type information in directory entries.

                          Allow bitmaps and inode tables for a block group to be placed anywhere on the storage media.
                          Tune2fs  will  not  reorganize  the  location of the inode tables and allocation bitmaps, as
                          mke2fs(8) will do when it creates a freshly formated file system with flex_bg enabled.

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

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

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

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

                          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  interna-
              tional  date  format,  with an optional time specifier, i.e.  YYYYMMDD[HH[MM[SS]]].   The keyword now is
              also accepted, in which case the last checked time will be set to the current time.

       -u user
              Set the user who can use the reserved filesystem blocks.  user can be a numerical uid or  a  user  name.
              If a user name is given, it is converted to a numerical uid before it is stored in the superblock.

       -U UUID
              Set  the  universally  unique  identifier (UUID) of the filesystem to UUID.  The format of the UUID is a
              series of hex digits separated by hyphens, like this: "c1b9d5a2-f162-11cf-9ece-0020afc76f16".  The  UUID
              parameter may also be one of the following:

                   clear  clear the filesystem UUID

                   random generate a new randomly-generated UUID

                   time   generate a new time-based UUID

              The  UUID  may  be  used  by  mount(8),  fsck(8),  and /etc/fstab(5) (and possibly others) by specifying
              UUID=uuid instead of a block special device name like /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-gen-
              erated 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 <chkATdata-hh.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)

E2fsprogs version 1.41.12          May 2010                         TUNE2FS(8)