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TUNE2FS(8)                  System Manager's Manual                 TUNE2FS(8)

       tune2fs - adjust tunable filesystem parameters on ext2/ext3 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 ] [ -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 filesystems.

       -c max-mount-counts
              Adjust  the  maximal mounts count between two filesystem checks.
              If max-mount-counts is 0 or -1, the number of times the filesys-
              tem 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.  Can be
              used in conjunction with -c to force an fsck on  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-

       -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

       -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.

                          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.

       -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 overriden 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-
                          try 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.

                          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.

                          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.

              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-

       -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

       -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.CardATlinux.org>.  It is cur-
       rently being maintained by Theodore Ts'o <tytsoATalum.edu>.  tune2fs
       uses the ext2fs library written by Theodore Ts'o <tytsoATmit.edu>.  This
       manual page was  written  by  Christian  Kuhtz  <chkATdata-hh.DE>.
       Time-dependent checking was added by Uwe Ohse <uweATtirka.de>.

       tune2fs  is  part  of  the  e2fsprogs  package  and  is  available from

       dumpe2fs(8), e2fsck(8), mke2fs(8)

E2fsprogs version 1.37            March 2005                        TUNE2FS(8)