TUNE2FS(8)                                                          TUNE2FS(8)
NAME
       tune2fs - adjust tunable filesystem parameters on ext2/ext3 filesystems

SYNOPSIS
       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 ] [ -L volume-name ] [ -M last-mounted-directory ] [
       -O [^]feature[,...]  ] [ -T time-last-checked ] [ -U UUID ] device

DESCRIPTION
       tune2fs  allows  the  system  administrator  to  adjust various tunable
       filesystem parameters on Linux ext2/ext3 filesystems.

OPTIONS
       -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
              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.

       -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-
              tion.

       -g group
              Set the group which can use  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 post-
              fix 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-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  to go unnoticed until they cause 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
              filesystem.

       -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:

                   size=journal-size
                          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.

                   device=external-journal
                          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
                          tune2fs(8).

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

       -l     List the contents of the filesystem superblock.

       -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 reserved filesystem blocks.

       -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.

                   bsdgroups
                          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 directory itself.

                   user_xattr
                          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.

                   journal_data
                          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.

                   journal_data_ordered
                          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.

                   journal_data_writeback
                          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
              tune2fs:

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

                   filetype
                          Store file type information in directory entries.

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

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

              After  setting  or clearing sparse_super and filetype 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 neces-
              sary.  After setting the dir_index feature, e2fsck -D can be run
              to convert existing directories to the hashed B-tree format.

              Warning: Linux kernels before 2.0.39 and many 2.1 series kernels
              do  not  support the filesystems that use any of these features.
              Enabling certain filesystem features may prevent the  filesystem
              from  being  mounted  by kernels which do not support those fea-
              tures.

       -r reserved-blocks-count
              Set the number of reserved filesystem blocks.

       -s [0|1]
              Turn the sparse super feature off or on.  Turning  this  feature
              on  saves  space on really big filesystems.  This is the same as
              using the -O sparse_super option.

              Warning: Linux kernels before 2.0.39 do not  support  this  fea-
              ture.   Neither  do all Linux 2.1 kernels; please don't use this
              unless you know what you're doing!  You need to run e2fsck(8) on
              the  filesystem  after  changing this feature in order to have a
              valid filesystem.

       -T time-last-checked
              Set the time the filesystem was last checked using e2fsck.  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[[HHMM]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 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.

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

AUTHOR
       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>.

AVAILABILITY
       tune2fs is  part  of  the  e2fsprogs  package  and  is  available  from
       http://e2fsprogs.sourceforge.net.

SEE ALSO
       dumpe2fs(8), e2fsck(8), mke2fs(8)

E2fsprogs version 1.39             May 2006                         TUNE2FS(8)