fallocate − preallocate or deallocate space to a file
fallocate [−n] [−p] [−o offset] −l length filename
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.
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-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
Punch holes in the file, the range should not exceed the length of the file.
−o, −−offset offset
Specifies the beginning offset of the allocation, in bytes.
−l, −−length length
Specifies the length of the allocation, in bytes.
−h, −−help
Display help text and exit.
-V, −−version
Display version information and exit.
fallocate(2), posix_fallocate(3), truncate(1)
The fallocate command is part of the util-linux package and is available from Linux Kernel Archive.