Provided by: e2fsprogs_1.46.3-1ubuntu3_amd64 bug


       tune2fs - adjust tunable filesystem parameters on ext2/ext3/ext4 filesystems


       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)

       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


       -c max-mount-counts
              Adjust  the  number  of  mounts  after  which  the  filesystem  will  be checked by
              e2fsck(8).  If max-mount-counts is the string "random", tune2fs will use  a  random
              value  between  20 and 40.  If max-mount-counts is 0 or -1, 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 when using journaled filesystems.

              Mount-count-dependent  checking  is disabled by default to avoid unanticipated long
              reboots while e2fsck does its  work.   If  you  are  concerned  about  file  system
              corruptions caused by potential hardware problems of kernel bugs, a better solution
              than mount-count-dependent checking is to use the e2scrub(8)  program.   This  does
              require placing the file system on an LVM volume, however.

       -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.

       -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 allocator.

                          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.

                          Enable the casefold feature in the super block and set encoding-name as
                          the  encoding  to  be used.  If encoding-name is not specified, utf8 is
                          used. The  encoding  cannot  be  altered  if  casefold  was  previously

                          Define  parameters  for  file name character encoding operations.  If a
                          flag is not changed using this parameter, its default  value  is  used.
                          encoding-flags  should  be  a  comma-separated  lists  of  flags  to be
                          enabled.  The flags  cannot  be  altered  if  casefold  was  previously

                          The  only  flag  that  can  be set right now is strict which means that
                          invalid strings should be rejected by the file system.  In the  default
                          configuration, the strict flag is disabled.

                          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 options 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 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 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 corruption.

       -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 suffix 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 operation can also take  a  while  and  the  file  system  can  be
              corrupted  and data lost if it is interrupted while in the middle of converting the
              file system.  Backing up the file system before changing inode size is recommended.

              File systems with an inode size of 128  bytes  do  not  support  timestamps  beyond
              January  19,  2038.   Inodes  which  are  256 bytes or larger will support extended
              timestamps, project id's, and the ability to store some extended attributes in  the
              inode table for improved performance.

       -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 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

              If  this  option  is used to create a journal on a mounted filesystem, 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  invisible,  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.

                          Create an additional fast commit journal area of size  fast-commit-size
                          kilobytes.  This option is only valid if fast_commit feature is enabled
                          on the file system. If this option is not specified and if  fast_commit
                          feature  is turned on, fast commit area size defaults to journal-size /
                          64 megabytes. The total size of the journal  with  fast_commit  feature
                          set  is  journal-size + ( fast-commit-size * 1024) megabytes. The total
                          journal size may be no more than 10,240,000 filesystem blocks  or  half
                          the total file system size (whichever is smaller).

                          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

                          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 currently support shared
                          external journals yet.

                          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 volume label and UUID.  See  also  the  -L  option  of

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

       -l     List the contents of the filesystem superblock, including the current values of the
              parameters that can be set via this program.

       -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 warning.   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 filesystem fragmentation, and to allow  system  daemons,
              such  as  syslogd(8),  to  continue  to  function  correctly  after  non-privileged
              processes are prevented from writing to  the  filesystem.   Normally,  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 filesystem.  Default mount
              options can be overridden 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 superblock.

              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 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 directory 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 interoperability 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 filesystem 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.

                          The  file system will be mounted with barrier operations in the journal
                          disabled.  (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 block_validity 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
                          overhead, so it is enabled only for debugging purposes.   (This  option
                          is  currently  only supported by the ext4 file system driver in 2.6.35+

                          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-provisioned
                          drives  available  in  some  enterprise  storage  arrays) to inform the
                          storage device that blocks belonging 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 allocation feature.  (This option is currently
                          only supported by the ext4 file system driver in 2.6.35+ kernels.)

       -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 system features, please see the man page ext4(5).

              The following filesystem features can be set or cleared using tune2fs:

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

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

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

                          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 number of extended attributes  per  file.   Tune2fs  currently
                          only supports setting this filesystem feature.

                          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

                          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 enabled.

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

                          Enable fast commit journaling feature to improve fsync latency.

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

                          Support files larger than 2 terabytes in size.

                          Filesystem can contain files that are greater than 2GB.

                          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 metadata_csum feature while it is mounted.

                   mmp    Enable or disable multiple mount protection (MMP) feature.

                          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 supports setting  this  filesystem

                          Prevent the filesystem from being shrunk or having its UUID changed, in
                          order to allow the use of specialized encryption settings that make use
                          of the inode numbers and UUID.  Tune2fs currently only supports setting
                          this filesystem feature.

                          Allow the kernel to initialize bitmaps and inode tables 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 feature  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

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

              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  consistent  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
              particular,  the  uninit_bg  and  flex_bg  features  are only supported by the ext4

       -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 corrupted 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 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  separated  by  hyphens,  like  this:
              "c1b9d5a2-f162-11cf-9ece-0020afc76f16".   The UUID parameter may also be one of the

                   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

              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 <>.  It is currently being  maintained
       by  Theodore  Ts'o  <>.   tune2fs  uses  the  ext2fs  library written by
       Theodore Ts'o <>.  This manual page was written by Christian Kuhtz <chk@data-
       hh.Hanse.DE>.  Time-dependent checking was added by Uwe Ohse <>.


       tune2fs    is    part    of    the    e2fsprogs    package    and    is   available   from


       debugfs(8), dumpe2fs(8), e2fsck(8), mke2fs(8), ext4(5)