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 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 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 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 len 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) and tmpfs (since Linux 3.5).

       -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.

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

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

AUTHORS

       Eric Sandeen ⟨sandeen@redhat.com⟩
       Karel Zak ⟨kzak@redhat.com⟩

SEE ALSO

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

AVAILABILITY

       The fallocate command is part of the util-linux package and is available from Linux Kernel
       Archive ⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩.