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, 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/⟩.