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 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.

       -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, subse-
              quent  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 preallo-
              cated 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 spec-
              ified 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/>.

util-linux                                                          April 2014                                                        FALLOCATE(1)