FALLOCATE(1)                                               User Commands                                               FALLOCATE(1)

       fallocate - preallocate or deallocate space to a file

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

       fallocate -d [-o offset] [-l length] filename

       fallocate -x [-o offset] -l length filename

       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.

       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.

           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
           Print version and exit.

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

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

       For bug reports, use the issue tracker at https://github.com/util-linux/util-linux/issues.

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

util-linux 2.38.1                                            2022-05-11                                                FALLOCATE(1)