FALLOCATE(1)                     User Commands                    FALLOCATE(1)



NAME
       fallocate - preallocate or deallocate space to a file

SYNOPSIS
       fallocate [-n] [-p] [-c] [-z] [-o offset] -l length filename

       fallocate -d [-o offset] [-l length] filename

DESCRIPTION
       fallocate  is  used  to manipulate the allocated disk space for a file,
       either to deallocate or preallocate it. For filesystems  which  support
       the  fallocate system call, preallocation is done quickly by allocating
       blocks and marking them as uninitialized, requiring no IO to  the  data
       blocks.  This  is  much  faster than creating a file by filling it with
       zeros.

       The exit code returned by fallocate is 0 on success and 1 on failure.

OPTIONS
       The length and offset arguments may be followed by  the  multiplicative
       suffixes KiB=1024, MiB=1024*1024, and so on for GiB, TiB, PiB, EiB, ZiB
       and YiB (the "iB" is optional, e.g. "K" has the same meaning as  "KiB")
       or the suffixes KB=1000, MB=1000*1000, and so on for GB, TB, PB, EB, ZB
       and YB.

       The options --collapse-range,  --dig-holes,  --punch-hole  and  --zero-
       range are mutually exclusive.


       -n, --keep-size
              Do  not modify the apparent length of the file.  This may effec-
              tively allocate blocks past EOF, which can  be  removed  with  a
              truncate.

       -p, --punch-hole
              Deallocates  space  (i.e.,  creates  a  hole)  in the byte range
              starting at offset and continuing for length bytes.  Within  the
              specified range, partial filesystem blocks are zeroed, and whole
              filesystem blocks are removed from the file.  After a successful
              call, subsequent reads from this range will return zeroes.  This
              option may not be specified at the same  time  as   the  --zero-
              range  option.   Also,  when  using  this option, --keep-size is
              implied.

              Supported for XFS (since Linux 2.6.38), ext4 (since Linux  3.0),
              Btrfs (since Linux 3.7) and tmpfs (since Linux 3.5).

       -d, --dig-holes
              Detect  and  dig  holes. Makes the file sparse in-place, without
              using extra disk space. The minimal size of the hole depends  on
              filesystem I/O block size (usually 4096 bytes). Also, when using
              this option, --keep-size is implied. If no range is specified by
              --offset and --length, then all file is analyzed for holes.

              You  can think of this as doing a "cp --sparse" and renaming the
              dest file as the original,  without  the  need  for  extra  disk
              space.

              See --punch-hole for list of the supported filesystems.

       -c, --collapse-range
              Removes  a  byte range from a file, without leaving a hole.  The
              byte range to be collapsed starts at offset  and  continues  for
              length  bytes.  At the completion of the operation, the contents
              of the file starting  at  the  location  offset+length  will  be
              appended  at  the  location  offset, and the file will be length
              bytes smaller. The option --keep-size may not be  specified  for
              colapse range operation.

              Available  since  Linux  3.15  for  ext4  (only for extent-based
              files) and XFS.

       -z, --zero-range
              Zeroes space in the byte range starting at offset and continuing
              for length bytes.  Within the specified range, blocks are preal-
              located for the regions that span the holes in the file.   After
              a  successful call, subsequent reads from this range will return
              zeroes.

              Zeroing is done within the filesystem preferably  by  converting
              the  range into unwritten extents.  This approach means that the
              specified range will not be physically zeroed out on the  device
              (except  for partial blocks at the either end of the range), and
              I/O is (otherwise) required only to update metadata.

              Option --keep-size can be specified to prevent file length modi-
              fication.

              Available  since  Linux  3.14  for  ext4  (only for extent-based
              files) and XFS.

       -o, --offset offset
              Specifies the beginning offset of the range, in bytes.

       -l, --length length
              Specifies the length of the range, in bytes.

       -h, --help
              Display help text and exit.

       -v, --verbose
              Enable verbose mode.

       -V, --version
              Display version information and exit.

AUTHORS
       Eric Sandeen <sandeen@redhat.com>
       Karel Zak <kzak@redhat.com>

SEE ALSO
       fallocate(2), posix_fallocate(3), truncate(1)

AVAILABILITY
       The fallocate command is part of the util-linux package and  is  avail-
       able  from  Linux  Kernel Archive <ftp://ftp.kernel.org/pub/linux/utils
       /util-linux/>.



util-linux                      September 2011                    FALLOCATE(1)
