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, 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.

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 at 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 2.39.3                                  2023-10-23                                       FALLOCATE(1)