fallocate — preallocate space to a file.
fallocate [−n] [ −o offset ] −l length filename
fallocate is used to preallocate blocks to a file. For filesystems which support the fallocate system call, this 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.
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.
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,
−−helpPrint help and exit.
−n,
−−keep−sizeDo not modify the apparent length of the file. This may effectively allocate blocks past EOF, which can be removed with a truncate.
−o,
−−offset offsetSpecifies the beginning offset of the allocation, in bytes.
−l,
−−length lengthSpecifies the length of the allocation, in bytes.