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fallocate — preallocate space to a file
fallocate [−n] [−p] [ −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 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.
−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.
−p,
−−punch−holePunch holes in the file, the range should not exceed the length of the file.
−o,
−−offset offsetSpecifies the beginning offset of the allocation, in bytes.
−l,
−−length lengthSpecifies the length of the allocation, in bytes.
−h,
−−helpDisplay help text and exit.
−V,
−−versionDisplay version information and exit.
The fallocate command is part of the util-linux package and is available from Linux Kernel Archive
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