Manual: fallocate

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 , Karel Zak 

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

REPORTING BUGS
       For bug reports, use the issue tracker .

AVAILABILITY
       The fallocate command is part of the util-linux package which can be downloaded from Linux Kernel Archive
       .

util-linux 2.41.3					 2025-12-15						FALLOCATE(1)