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
       Karel Zak

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.

util-linux                                         April 2014                                       FALLOCATE(1)