fallocate(1)

NAME

   fallocate - preallocate or deallocate space to a file

SYNOPSIS

   fallocate [-c|-p|-z] [-o offset] -l length [-n] 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
   zeroes.

   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.

   -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
          the collapse-range operation.

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

   -d, --dig-holes
          Detect and dig holes.  This  makes  the  file  sparse  in-place,
          without  using  extra  disk space.  The minimum 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  the  entire
          file is analyzed for holes.

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

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

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

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

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

   -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).

   -v, --verbose
          Enable verbose mode.

   -z, --zero-range
          Zeroes space in the byte range starting at offset and continuing
          for length  bytes.   Within  the  specified  range,  blocks  are
          preallocated  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
          modification.

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

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

   -h, --help
          Display help text 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
   available from  Linux  Kernel  Archive  ftp://ftp.kernel.org/pub/linux
   /utils/util-linux/.

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Free and Open Source Software