linux man page for fallocate

FALLOCATE(1)						      General Commands Manual						      FALLOCATE(1)

NAME
       fallocate - preallocate space to a file.

SYNOPSIS
       fallocate [-n] [-o offset] -l length filename

DESCRIPTION
       fallocate  is used to preallocate blocks to a file.  For filesystems which support the fallocate system call, this is done quickly by allo-
       cating 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.

       As of the Linux Kernel v2.6.31, the fallocate system call is supported by the btrfs, ext4, ocfs2, and xfs filesystems.

       The exit code returned by fallocate is 0 on success and 1 on failure.

OPTIONS
       The  length  and  offset arguments may be followed by binary (2^N) suffixes KiB, MiB, GiB, TiB, PiB and EiB (the "iB" is optional, e.g. "K"
       has the same meaning as "KiB") or decimal (10^N) suffixes KB, MB, GB, PB and EB.

       -h, --help
	      Print help and exit.

       -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 allocation, in bytes.

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

AUTHORS
       Eric Sandeen <sandeen@redhat.com>
       Karel Zak <kzak@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 ftp://ftp.kernel.org/pub/linux/utils/util-linux/.

Version 1.0							     Jul 2009							      FALLOCATE(1)