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(2) 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 status 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, --zero-range
       and --posix 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.

	   A filesystem may place limitations on the granularity of the
	   operation, in order to ensure efficient implementation. Typically,
	   offset and length must be a multiple of the filesystem logical
	   block size, which varies according to the filesystem type and
	   configuration. If a filesystem has such a requirement, the
	   operation will fail with the error EINVAL if this requirement is
	   violated.

       -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,
	   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), tmpfs (since Linux 3.5) and gfs2 (since
	   Linux 4.16).

       -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
	   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.

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

       -V, --version
	   Display version and exit.

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

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

REPORTING BUGS
       For bug reports, use the issue tracker
       <https://github.com/util-linux/util-linux/issues>.

AVAILABILITY
       The fallocate command is part of the util-linux package which can be
       downloaded from Linux Kernel Archive
       <https://www.kernel.org/pub/linux/utils/util-linux/>.

util-linux 2.41.2		  2025-09-22			  FALLOCATE(1)