FALLOCATE(1)                              User Commands                              FALLOCATE(1)



NAME
       fallocate - preallocate or deallocate space to a file

SYNOPSIS
       fallocate [-n] [-p] [-c] [-z] [-o offset] -l length filename

       fallocate -d [-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 zeros.

       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.


       -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.

       -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 suc‐
              cessful 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).

       -d, --dig-holes
              Detect  and  dig  holes.  Makes  the file sparse in-place, without using extra disk
              space. The minimal 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 all file is analyzed for holes.

              You can think of this as doing a "cp --sparse" and renaming the dest  file  as  the
              original, without the need for extra disk space.

              See --punch-hole for list of the supported filesystems.

       -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 colapse range operation.

              Available since Linux 3.15 for ext4 (only for extent-based files) and XFS.

       -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 physi‐
              cally 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.

       -o, --offset offset
              Specifies the beginning offset of the range, in bytes.

       -l, --length length
              Specifies the length of the range, in bytes.

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

       -v, --verbose
              Enable verbose mode.

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

AUTHORS
       Eric Sandeen ⟨sandeen AT redhat.com⟩
       Karel Zak ⟨kzak AT redhat.com⟩

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

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



util-linux                                September 2011                             FALLOCATE(1)