Provided by: e2fsprogs_1.47.1-1ubuntu1_amd64 bug

NAME

       tune2fs - adjust tunable file system parameters on ext2/ext3/ext4 file systems

SYNOPSIS

       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

DESCRIPTION

       tune2fs allows the system administrator to adjust various tunable file  system  parameters
       on  Linux  ext2,  ext3,  or ext4 file systems.  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).

OPTIONS

       -c max-mount-counts
              Adjust  the  number  of  mounts  after  which  the  file  system 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
              file system is mounted will be disregarded by e2fsck(8) and the kernel.

              Staggering the mount-counts at which file systems are forcibly checked  will  avoid
              all file systems being checked at one time when using journaled file systems.

              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 file system 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 file system at the next reboot.

       -e error-behavior
              Change  the  behavior of the kernel code when errors are detected.  In all cases, a
              file system error will cause e2fsck(8) to check the file system on the  next  boot.
              error-behavior can be one of the following:

                   continue    Continue normal execution.

                   remount-ro  Remount file system read-only.

                   panic       Cause a kernel panic.

       -E extended-options
              Set  extended  options  for the file system.  Extended options are comma separated,
              and may take an argument using the  equals  ('=')  sign.   The  following  extended
              options are supported:

                   clear_mmp
                          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 file system corruption can result.  Needs '-f'.

                   mmp_update_interval=interval
                          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.

                   stride=stride-size
                          Configure the file system for a RAID array with stride-size file system
                          blocks.  This  is  the  number of blocks read or written to disk before
                          moving to next disk. This  mostly  affects  placement  of  file  system
                          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.

                   stripe_width=stripe-width
                          Configure  the  file  system  for  a  RAID array with stripe-width file
                          system 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.

                   hash_alg=hash-alg
                          Set the default hash algorithm used for file systems with hashed b-tree
                          directories.  Valid algorithms accepted are: legacy, half_md4, and tea.

                   encoding=encoding-name
                          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
                          enabled.

                   encoding_flags=encoding-flags
                          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
                          enabled.

                          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.

                   mount_opts=mount_option_string
                          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.

                   orphan_file_size=size
                          Set size of the file for tracking unlinked but still  open  inodes  and
                          inodes  with  truncate  in  progress.  Larger  file  allows  for better
                          scalability, reserving a few blocks per cpu is ideal.

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

                   test_fs
                          Set  a  flag  in  the  file system superblock indicating that it may be
                          mounted using experimental  kernel  code,  such  as  the  ext4dev  file
                          system.

                   ^test_fs
                          Clear  the  test_fs  flag,  indicating  the  file system should only be
                          mounted using production-level file system code.

       -f     Force the tune2fs operation to complete even in the face of errors.  This option is
              useful  when  removing the has_journal file system feature from a file system 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 file system appears
              to require journal replay, the -f flag must be specified twice to proceed.

              WARNING: Removing an external journal from a file  system  which  was  not  cleanly
              unmounted  without  first  replaying the external journal can result in severe data
              loss and file system corruption.

       -g group
              Set the group which can use the reserved file system 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 file  system  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 file system.  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 file system) stored within the file system.  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 file system,  an  immutable
              file,  .journal,  will be created in the top-level directory of the file system, as
              it is the only safe way to create the  journal  inode  while  the  file  system  is
              mounted.  While the ext3 journal is visible, it is not safe to delete it, or modify
              it while the file system is mounted; for this reason the file is marked  immutable.
              While  checking  unmounted file systems, e2fsck(8) will automatically move .journal
              files to the invisible, reserved journal inode.  For all file  systems  except  for
              the  root  file  system,  this should happen automatically and naturally during the
              next reboot cycle.  Since the root file system 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  file  system  to  ext3  if  the
              /etc/fstab file specifies the ext3 file system for the root file system in order to
              avoid requiring the use of a rescue floppy to add an ext3 journal to the root  file
              system.

       -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  the  file  system  of size journal-size
                          megabytes.   The size of the journal must be at least 1024 file  system
                          blocks  (i.e.,  1MB  if  using 1k blocks, 4MB if using 4k blocks, etc.)
                          and may be no more than 10,240,000 file system blocks.  There  must  be
                          enough free space in the file system to create a journal of that size.

                   fast_commit_size=fast-commit-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 file system blocks or half
                          the total file system size (whichever is smaller).

                   location=journal-location
                          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.

                   device=external-journal
                          Attach the file system 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 file systems which will be using it.  In addition,  while  there  is
                          support  for  attaching  multiple  file  systems  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
                          tune2fs(8).

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

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

       -L volume-label
              Set the volume label of the file system.  Ext2 file system labels can be at most 16
              characters long; if  volume-label  is  longer  than  16  characters,  tune2fs  will
              truncate  it and print a warning.  For other file systems that support online label
              manipulation and are mounted tune2fs will work as well, but it will not attempt  to
              truncate  the  volume-label  at  all.   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 file system which may only be allocated by privileged
              processes.   Reserving some number of file system  blocks  for  use  by  privileged
              processes  is done to avoid file system 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 file system.  Normally, the default
              percentage of reserved blocks is 5%.

       -M last-mounted-directory
              Set the last-mounted directory for the file system.

       -o [^]mount-option[,...]
              Set or clear the indicated default mount options in the file system.  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
              file system's superblock; mount options without a prefix character or prefixed with
              a plus character ('+') will be added to the file system.

              The following mount options can be set or cleared using tune2fs:

                   debug  Enable debugging code for this file system.

                   bsdgroups
                          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.

                   user_xattr
                          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.

                   journal_data
                          When  the file system is mounted with journaling enabled, all data (not
                          just metadata) is committed into the journal  prior  to  being  written
                          into the main file system.

                   journal_data_ordered
                          When  the  file  system is mounted with journaling enabled, all data is
                          forced directly out to the main file system prior to its metadata being
                          committed to the journal.

                   journal_data_writeback
                          When  the  file  system is mounted with journaling enabled, data may be
                          written into the main file system 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.

                   nobarrier
                          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.)

                   block_validity
                          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+
                          kernels.)

                   discard
                          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.)

                   nodelalloc
                          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 file system features (options) in the file system.  More
              than one file system feature can be cleared or  set  by  separating  features  with
              commas.  File System features prefixed with a caret character ('^') will be cleared
              in the file system's superblock; file system features without a prefix character or
              prefixed  with  a  plus  character  ('+')  will be added to the file system.  For a
              detailed description of the file system features, please see the man page ext4(5).

              The following file system features can be set or cleared using tune2fs:

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

                   casefold
                          Enable support for file system level casefolding.  The  option  can  be
                          cleared only if filesystem has no directories with F attribute.

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

                   dir_nlink
                          Allow more than 65000 subdirectories per directory.

                   ea_inode
                          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 file system feature.

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

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

                   extra_isize
                          Enable the extended inode fields used by ext4.

                   filetype
                          Store file type information in directory entries.

                   flex_bg
                          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.

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

                   fast_commit
                          Enable fast commit journaling feature to improve fsync latency.

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

                   huge_file
                          Support files larger than 2 terabytes in size.

                   large_file
                          File System can contain files that are greater than 2GB.

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

                   metadata_csum_seed
                          Allow  the  file  system  to  store  the  metadata checksum seed in the
                          superblock, enabling the administrator to change the  UUID  of  a  file
                          system using the metadata_csum feature while it is mounted.

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

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

                   quota  Enable internal file system quota inodes.

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

                   resize_inode
                          Reserve  space  so  the  block  group  descriptor table may grow in the
                          future.  Tune2fs only supports clearing this file system feature.

                   sparse_super
                          Limit the number of backup superblocks to  save  space  on  large  file
                          systems.   Tune2fs  currently  only  supports  setting this file system
                          feature.

                   stable_inodes
                          Prevent the file system 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 file system feature.

                   uninit_bg
                          Allow  the kernel to initialize bitmaps and inode tables lazily, and to
                          keep a high watermark for the unused inodes in a file system, 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
                          is.

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

              After  setting  or clearing sparse_super, uninit_bg, filetype, or resize_inode file
              system features, the file system may  require  being  checked  using  e2fsck(8)  to
              return  the  file  system  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 file system features may prevent  the  file
              system  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  file
              system.

       -r reserved-blocks-count
              Set the number of reserved file system 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:

                   [^]usrquota
                          Sets/clears user quota inode in the superblock.

                   [^]grpquota
                          Sets/clears group quota inode in the superblock.

                   [^]prjquota
                          Sets/clears project quota inode in the superblock.

       -T time-last-checked
              Set the time  the  file  system  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 file  system,
              and  then  check  the  file  system  during  off  hours to make sure it hasn't been
              corrupted due to hardware problems, etc.  If the file system was clean,  then  this
              option  can  be used to set the last checked time on the original file system.  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 file system 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  file  system  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
              following:

                   clear  clear the file system 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.

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 currently 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

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