TUNE2FS(8)                  System Manager's Manual                 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 ] [ -I new_inode_size ] [ -j ] [ -J journal-
       options ] [ -m reserved-blocks-percentage ] [ -o [^]mount-options[,...]
       ]  [  -r  reserved-blocks-count  ] [ -u user ] [ -g group ] [ -C mount-
       count ] [ -E extended-options ] [ -L volume-label ] [ -M  last-mounted-
       directory  ]  [  -O [^]feature[,...]  ] [ -Q quota-options ] [ -T time-
       last-checked ] [ -U UUID ] [ -z undo_file ] 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.

       The  device  specifier can either be a filename (i.e., /dev/sda1), or a
       LABEL or UUID specifier: "LABEL=volume-label" or  "UUID=uuid".   (i.e.,
       LABEL=home or UUID=e40486c6-84d5-4f2f-b99c-032281799c9d).

       -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.

              Mount-count-dependent checking is disabled by default  to  avoid
              unanticipated long reboots while e2fsck does its work.  However,
              you may wish to 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 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:

                          Reset the MMP block  (if  any)  back  to  the  clean
                          state.  Use only if absolutely certain the device is
                          not currently mounted  or  being  fscked,  or  major
                          filesystem corruption can result.  Needs '-f'.

                          Adjust  the  initial MMP update interval to interval
                          seconds.  Specifying an interval of 0 means  to  use
                          the  default  interval.  The specified interval must
                          be less than 300 seconds.   Requires  that  the  mmp
                          feature be enabled.

                          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 set of default mount  options  which  will  be
                          used  when  the  file system is mounted.  Unlike the
                          bitmask-based default mount  options  which  can  be
                          specified with the -o option, mount_option_string is
                          an arbitrary string with  a  maximum  length  of  63
                          bytes, which is stored in the superblock.

                          The  ext4  file  system  driver will first apply the
                          bitmask-based default options, and  then  parse  the
                          mount_option_string,  before  parsing  the mount op-
                          tions passed from the mount(8) program.

                          This superblock setting is only honored  in  2.6.35+
                          kernels;  and  not  at all by the ext2 and ext3 file
                          system drivers.

                          Set a flag in the filesystem  superblock  indicating
                          that  errors  have been found.  This will force fsck
                          to run at the next mount.

                          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  er-
              rors.   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.    If  the
              filesystem  appears  to require journal replay, the -f flag must
              be specified twice to proceed.

              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.

              There  are pros and cons to disabling these periodic checks; see
              the discussion under the -c (mount-count-dependent check) option
              for details.

       -I     Change  the  inode size used by the file system.   This requires
              rewriting the inode table, so it requires that the  file  system
              is  checked  for consistency first using e2fsck(8).  This opera-
              tion can also take a while and the file system can be  corrupted
              and  data  lost if it is interrupted while in the middle of con-
              verting the file system.

       -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  10,240,000  filesystem
                          blocks.   There  must  be  enough  free space in the
                          filesystem to create a journal of that size.

                          Specify the location of the journal.   The  argument
                          journal-location  can either be specified as a block
                          number, or if the number has a units  suffix  (e.g.,
                          'M',  'G', etc.) interpret it as the offset from the
                          beginning of the file system.

                          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 us-
                          ing it.  In addition, while there is support for at-
                          taching  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  LA-
                          BEL=label  or UUID=UUID to locate the external jour-
                          nal 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 la-
                          bel and UUID.  See also the -L option of tune2fs(8).

              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=volume-
              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 behavior when creating new  files:  they
                          will  take  the  group-id  of the directory in which
                          they were created.  The standard System  V  behavior
                          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 en-
                          abled, 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  en-
                          abled,  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 en-
                          abled, data may be written into the main  filesystem
                          after  its  metadata has been committed to the jour-
                          nal.  This may increase throughput, however, it  may
                          allow  old data to appear in files after a crash and
                          journal recovery.

                          The file system will be mounted with barrier  opera-
                          tions in the journal disabled.  (This option is cur-
                          rently only supported by the ext4 file system driver
                          in 2.6.35+ kernels.)

                          The  file  system will be mounted with the block_va-
                          lidity option enabled, which causes extra checks  to
                          be  performed after reading or writing from the file
                          system.  This  prevents  corrupted  metadata  blocks
                          from causing file system damage by overwriting parts
                          of the inode table or block group descriptors.  This
                          comes  at the cost of increased memory and CPU over-
                          head, so it is enabled only for debugging  purposes.
                          (This option is currently only supported by the ext4
                          file system driver in 2.6.35+ kernels.)

                          The file system will be  mounted  with  the  discard
                          mount  option.   This  will  cause  the  file system
                          driver to attempt to use the trim/discard feature of
                          some  storage devices (such as SSD's and thin-provi-
                          sioned drives available in some  enterprise  storage
                          arrays) to inform the storage device that blocks be-
                          longing to deleted files can  be  reused  for  other
                          purposes.   (This option is currently only supported
                          by the ext4 file system driver in 2.6.35+ kernels.)

                          The file system will be mounted with the  nodelalloc
                          mount option.  This will disable the delayed alloca-
                          tion feature.  (This option is currently  only  sup-
                          ported  by  the  ext4  file system driver in 2.6.35+

       -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.  For a detailed description of the file  sys-
              tem features, please see the man page ext4(5).

              The  following  filesystem  features can be set or cleared using

                   64bit  Enable the  file  system  to  be  larger  than  2^32

                          Use hashed b-trees to speed up lookups for large di-

                          Allow more than 65000 subdirectories per directory.

                          Allow the value of each  extended  attribute  to  be
                          placed  in  the  data  blocks of a separate inode if
                          necessary, increasing the limit on the size and num-
                          ber  of  extended attributes per file.  Tune2fs cur-
                          rently only supports setting  this  filesystem  fea-

                          Enable  support  for  file  system level encryption.
                          Tune2fs  currently  only   supports   setting   this
                          filesystem feature.

                   extent Enable the use of extent trees to store the location
                          of data blocks in inodes.   Tune2fs  currently  only
                          supports setting this filesystem feature.

                          Enable the extended inode fields used by ext4.

                          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 formatted 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.

                          Increase the limit on the number of files per direc-
                          tory.   Tune2fs currently only supports setting this
                          filesystem feature.

                          Support files larger than 2 terabytes in size.

                          Filesystem can contain files that are  greater  than

                          Store  a  checksum  to  protect the contents in each
                          metadata block.

                          Allow the filesystem to store the metadata  checksum
                          seed  in  the superblock, enabling the administrator
                          to change the UUID of a filesystem using  the  meta-
                          data_csum feature while it is mounted.

                   mmp    Enable  or  disable  multiple mount protection (MMP)

                          Enable  project  ID  tracking.   This  is  used  for
                          project quota tracking.

                   quota  Enable internal file system quota inodes.

                          Force the kernel to mount the file system read-only.

                          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.  Tune2fs currently  only  sup-
                          ports setting this filesystem feature.

                          Allow the kernel to initialize bitmaps and inode ta-
                          bles lazily, and to keep a high  watermark  for  the
                          unused  inodes  in a filesystem, to reduce e2fsck(8)
                          time.  The first e2fsck run after enabling this fea-
                          ture  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.

                   verity Enable  support for verity protected files.  Tune2fs
                          currently only supports setting this filesystem fea-

              After  setting or clearing sparse_super, uninit_bg, filetype, or
              resize_inode filesystem features, the file  system  may  require
              being checked using e2fsck(8) to return the filesystem to a con-
              sistent state.  Tune2fs will print a message requesting that the
              system  administrator 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 par-
              ticular, 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.

       -Q quota-options
              Sets  'quota'  feature  on the superblock and works on the quota
              files for the given quota type. Quota options could  be  one  or
              more of the following:

                          Sets/clears user quota inode in the superblock.

                          Sets/clears group quota inode in the superblock.

                          Sets/clears project quota inode in the superblock.

       -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.

       -z undo_file
              Before overwriting a file system block, write the  old  contents
              of  the  block to an undo file.  This undo file can be used with
              e2undo(8) to restore the old contents of the file system  should
              something  go  wrong.   If  the  empty  string  is passed as the
              undo_file argument, the undo file will  be  written  to  a  file
              named  tune2fs-device.e2undo  in the directory specified via the
              E2FSPROGS_UNDO_DIR environment variable.

              WARNING: The undo file cannot be used to recover from a power or
              system crash.

       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), ext4(5)

E2fsprogs version 1.45.5         January 2020                       TUNE2FS(8)
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