TUNE2FS linux command manual

TUNE2FS(8)                                                         TUNE2FS(8)

       tune2fs  -  adjust tunable filesystem parameters on ext2/ext3 filesys-

       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-direc-
       tory  ]  [ -O [^]feature[,...]  ] [ -T time-last-checked ] [ -U UUID ]

       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 then 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
              filesystem error detected by the kernel  will  still  force  an
              fsck on the next reboot, but it may already be too late to pre-
              vent 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 filesys-
              tem 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
              journal (or is corrupted such that it appears to have an exter-
              nal 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
              postfix 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 cre-
              ate 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.

       -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,
                          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  vol-
                          ume  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

       -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
              filesystem.  Default mount options can be  overriden  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 certainly ignore the default mount options field in  the

              More  than one mount option can be cleared or set by separating
              features with commas.  Mount  options  prefixed  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

                   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 inter-
                          operability 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  com-
                          mutted 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 commutted 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  nec-

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

       -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  corrupted due to hardware problems, etc.  If the filesys-
              tem 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 sep-
              arated         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 .   It  is  cur-
       rently   being   maintained  by  Theodore  Ts'o  .
       tune2fs  uses  the   ext2fs   library   written   by   Theodore   Ts'o
       .   This  manual  page  was  written by Christian Kuhtz
       .  Time-dependent checking was added by Uwe Ohse

       tune2fs  is  part  of  the  e2fsprogs  package  and  is available from

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

E2fsprogs version 1.35          February 2004                      TUNE2FS(8)