FALLOCATE(1)							   User Commands						      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

       fallocate -x [-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.

       -i, --insert-range
	      Insert a hole of length bytes from offset, shifting existing data.

       -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, subse-
	      quent  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.

       -x, --posix
	      Enable POSIX operation mode. In that mode allocation operation always completes, but it may take longer time when fast allocation is
	      not supported by the underlying filesystem.

       -z, --zero-range
	      Zeroes  space in the byte range starting at offset and continuing for length bytes.  Within the specified range, blocks are preallo-
	      cated 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 spec-
	      ified 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

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

AVAILABILITY

       The  fallocate command is part of the util-linux package and is available from Linux Kernel Archive <https://www.kernel.org/pub/linux/utils
       /util-linux/>.

util-linux							    April 2014							      FALLOCATE(1)