*BASH User Commands Ubuntu 10.04.4 LTS Server coreutils
TUNE2FS(8)                                                          TUNE2FS(8)

       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  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

       -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  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  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 jour-
              nal (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 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.

              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

       -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 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%.

       -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.

                          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  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.

       -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

                          Use  hashed  b-trees  to  speed  up lookups in large

                          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

                          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  supports
                          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 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.

       -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 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

       -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 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)

E2fsprogs version 1.41.11         March 2010                        TUNE2FS(8)