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

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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 maximal mounts count between two  filesystem  checks.
              If max-mount-counts is 0 then 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(1,2,n)
              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(1,8) 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(8,n) 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(1,8)  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(8,n) 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(1,8) 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(1,8) 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(1,8) the superblock.

       -i  interval-between-checks[d|m|w]
              Adjust the maximal time(1,2,n) between two filesystem checks.  No post-
              fix or d result in(1,8) days, m in(1,8) months, and w in(1,8) 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(1,8) 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:

                   size=journal-size
                          Create  a  journal  stored in(1,8) the filesystem of size
                          journal-size megabytes.   The size  of  the  journal
                          must  be  at least 1024 filesystem blocks (i.e., 1MB
                          if(3,n) using 1k blocks, 4MB if(3,n) using  4k  blocks,  etc.)
                          and  may  be no more than 102,400 filesystem blocks.
                          There must be enough free space in(1,8) 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.

                          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(1,8)
                          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(3,n)  volume-label  is  longer
              than  16  characters, tune2fs will truncate(2,7) it and print a warn-
              ing.  The volume label can be used  by  mount(2,8)(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(1,3x,3x clrtobot) the indicated default mount(2,8) options in(1,8) the filesys-
              tem.  Default mount(2,8) options can be overriden  by  mount(2,8)  options
              specified  either  in(1,8) /etc/fstab(5) or on the command line argu-
              ments to mount(2,8)(8).  Older kernels may not support this  feature;
              in(1,8)  particular,  kernels  which  predate 2.4.20 will almost cer-
              tainly ignore the default mount(2,8) options field in(1,8) the superblock.

              More  than  one mount(2,8) option can be cleared or set(7,n,1 builtins) by separating
              features with commas.  Mount options prefixed with a caret char-
              acter  ('^')  will  be  cleared  in(1,8) the filesystem's superblock;
              mount(2,8) options without a prefix character or prefixed with a plus
              character ('+') will be added to the filesystem.

              The following mount(2,8) options can be set(7,n,1 builtins) 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(1,8) 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(7,n,1 builtins), in(1,8) which case it takes
                          the gid from the parent directory, and also gets(3,n) the
                          setgid bit set(7,n,1 builtins) if(3,n) 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(1,n) system prior to its metadata being commutted 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 commutted to the
                          journal.  This may increase throughput, however,  it
                          may  allow old data to appear in(1,8) files after a crash
                          and journal recovery.

       -O [^]feature[,...]
              Set or clear(1,3x,3x clrtobot) the indicated filesystem features (options) in(1,8)  the
              filesystem.   More than one filesystem feature can be cleared or
              set(7,n,1 builtins) by separating features  with  commas.   Filesystem  features
              prefixed  with  a  caret  character ('^') will be cleared in(1,8) 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(7,n,1 builtins)  or  cleared  using
              tune2fs:

                   dir_index
                          Use  hashed  b-trees  to  speed  up lookups in(1,8) large
                          directories.

                   filetype
                          Store file(1,n) type information in(1,8) 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(3,n) neces-
              sary.

              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(1,8) order  to  have  a
              valid filesystem.

       -T time-last-checked
              Set the time(1,2,n) the filesystem was last checked using e2fsck.  This
              can be useful in(1,8) 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(7,n,1 builtins) the last checked time(1,2,n)
              on  the original filesystem.  The format of time-last-checked is
              the international date format, with an optional time(1,2,n)  specifier,
              i.e.  YYYYMMDD[[HHMM]SS].   The keyword now is also accepted, in(1,8)
              which case the last checked time(1,2,n) will  be  set(7,n,1 builtins)  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(1,8) 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(1,3x,3x clrtobot)  clear(1,3x,3x clrtobot) the filesystem UUID

                   random(3,4,6) generate a new randomly-generated UUID

                   time(1,2,n)   generate a new time-based UUID

              The UUID may be used by  mount(2,8)(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(3,4,6)  number  generator  such as /dev/random(3,4,6) 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(1,3,5) 1.35           February 2004                      TUNE2FS(8)

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