fallocate(1) - preallocate or deallocate space to a file

[giantpanda]

FALLOCATE(1)			 User Commands			  FALLOCATE(1)

NAME
       fallocate - preallocate or deallocate space to a file

SYNOPSIS
       fallocate [-c] [-n] [-p] [-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.

       -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.

       -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 effec‐
	      tively 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 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.

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

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

AUTHORS
       Eric Sandeen ⟨[email protected]⟩
       Karel Zak ⟨[email protected]⟩

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)