fallocate

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 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 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), 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.

       -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)