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    Command:

    tune2fs

    
    
    
    

    SYNOPSIS

           tune2fs [ -l ] [ -c max-mount-counts ] [ -e errors-behavior ] [ -f ]  [
           -i  interval-between-checks  ]  [  -j  ]  [  -J  journal-options ] [ -m
           reserved-blocks-percentage  ]  [  -o  [^]mount-options[,...]   ]  [  -r
           reserved-blocks-count ] [ -s sparse-super-flag ] [ -u user ] [ -g group
           ] [ -C mount-count ] [ -E extended-options ] [ -L volume-name  ]  [  -M
           last-mounted-directory  ]  [  -O  [^]feature[,...]   ]  [ -T time-last-
           checked ] [ -U UUID ] device
    
    
    

    DESCRIPTION

           tune2fs allows the  system  administrator  to  adjust  various  tunable
           filesystem  parameters  on  Linux ext2, ext3, 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.
    
    
    

    OPTIONS

           -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.
    
                  You should  strongly  consider  the  consequences  of  disabling
                  mount-count-dependent   checking  entirely.   Bad  disk  drives,
                  cables, memory, and kernel bugs could all corrupt  a  filesystem
                  without  marking  the  filesystem dirty or in error.  If you are
                  using journaling on your filesystem, your filesystem will  never
                  be marked dirty, so it will not normally be checked.  A filesys-
                  tem 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
                  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.
                              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-
                              tor.
    
                       stripe_width=stripe-width
                              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.
    
                       hash_alg=hash-alg
                              Set  the default hash algorithm used for filesystems
                              with hashed b-tree  directories.   Valid  algorithms
                              accepted are: legacy, half_md4, and tea.
    
                       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.
    
                       test_fs
                              Set  a  flag in the filesystem superblock indicating
                              that it may be  mounted  using  experimental  kernel
                              code, such as the ext4dev filesystem.
    
                       ^test_fs
                              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 jour-
                  nal (or is corrupted such that it appears to  have  an  external
                  journal),  but  that external journal is not available.   If the
    
           -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.
    
                  It is strongly recommended that  either  -c  (mount-count-depen-
                  dent)  or -i (time-dependent) checking be enabled to force peri-
                  odic full e2fsck(8) checking of the filesystem.  Failure  to  do
                  so  may lead to filesystem corruption (due to bad disks, cables,
                  memory, or kernel bugs) going unnoticed, ultimately resulting in
                  data loss or corruption.
    
           -j     Add  an ext3 journal to the filesystem.  If the -J option is not
                  specified, the default journal parameters will be used to create
                  an  appropriately  sized journal (given the size of the filesys-
                  tem) stored within the filesystem.  Note that you must be  using
                  a kernel which has ext3 support in 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
                  filesystem.
    
           -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 filesystem of size
                              journal-size megabytes.   The size  of  the  journal
                              must  be  at least 1024 filesystem blocks (i.e., 1MB
                              if using 1k blocks, 4MB if using  4k  blocks,  etc.)
                              and  may  be no more than 102,400 filesystem blocks.
                              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
                              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
                  filesystem.
    
           -l     List the contents of the filesystem  superblock,  including  the
                  current  values  of the parameters that can be set via this pro-
                  gram.
    
           -L volume-label
                  Set the volume label of the filesystem.  Ext2 filesystem  labels
                  can  be  at  most  16 characters long; if volume-label is longer
                  than 16 characters, tune2fs will truncate it and print  a  warn-
                  ing.   The  volume  label  can be used by mount(8), fsck(8), and
                  /etc/fstab(5) (and possibly  others)  by  specifying  LABEL=vol-
                  ume_label instead of a block special device name like /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.
    
                       user_xattr
                              Enable user-specified extended attributes.
    
                       acl    Enable Posix Access Control Lists.
    
                       uid16  Disables 32-bit UIDs and GIDs.  This is for interop-
                              erability  with  older  kernels which only store and
                              expect 16-bit values.
    
                       journal_data
                              When the  filesystem  is  mounted  with  journalling
                              enabled,  all  data (not just metadata) is committed
                              into the journal prior to  being  written  into  the
                              main filesystem.
    
                       journal_data_ordered
                              When  the  filesystem  is  mounted  with journalling
                              enabled, all data is forced directly out to the main
                              file system prior to its metadata being committed to
                              the journal.
    
                       journal_data_writeback
                              When the  filesystem  is  mounted  with  journalling
                              enabled,  data may be written into the main filesys-
                              tem after its metadata has  been  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 opera-
                              tions in the journal disabled.  (This option is cur-
                              rently 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  overwrit-
                              ing parts of the inode table or block group descrip-
                              tors.  This comes at the cost  of  increased  memory
                              and  CPU  overhead, so it is enabled only for debug-
                              ging purposes.  (This option is currently only  sup-
                              ported  by  the  ext4  file system driver in 2.6.35+
                              kernels.)
    
                       discard
                              The file system will be mouinted  with  the  discard
                              mount  option.   This  will  cause  the  file system
    
           -O [^]feature[,...]
                  Set  or clear the indicated filesystem features (options) in the
                  filesystem.  More than one filesystem feature can be cleared  or
                  set  by  separating  features  with commas.  Filesystem features
                  prefixed with a caret character ('^') will  be  cleared  in  the
                  filesystem's  superblock;  filesystem  features without a prefix
                  character or prefixed with a plus character ('+') will be  added
                  to the filesystem.
    
                  The  following  filesystem  features can be set or cleared using
                  tune2fs:
    
                       dir_index
                              Use hashed b-trees to  speed  up  lookups  in  large
                              directories.
    
                       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 formated file system with flex_bg
                              enabled.
    
                       has_journal
                              Use a journal to ensure filesystem consistency  even
                              across  unclean  shutdowns.   Setting the filesystem
                              feature is equivalent to using the -j option.
    
                       large_file
                              Filesystem can contain files that are  greater  than
                              2GB.  (Modern kernels set this feature automatically
                              when a file > 2GB is created.)
    
                       resize_inode
                              Reserve space so the block  group  descriptor  table
                              may  grow  in  the  future.   Tune2fs  only supports
                              clearing this filesystem feature.
    
                       sparse_super
                              Limit the number of backup superblocks to save space
                              on large filesystems.
    
                       uninit_bg
                              Allow  the  kernel  to  initialize bitmaps and inode
                              tables and keep a  high  watermark  for  the  unused
                              inodes  in  a  filesystem, to reduce e2fsck(8) time.
                              This first e2fsck run after  enabling  this  feature
    
           -r reserved-blocks-count
                  Set the number of reserved filesystem blocks.
    
           -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
                  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 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.
    
    
    

    BUGS

           We haven't found any bugs yet.  That doesn't mean there aren't any...
    
    
    

    AUTHOR

           tune2fs  was  written  by  Remy Card <Remy.Card@linux.org>.  It is cur-
           rently being maintained by Theodore Ts'o <tytso@alum.mit.edu>.  tune2fs
    
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