Section: User Commands (1)
Updated: September 2011
fallocate [-n] [-p] [-c] [-z] [-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.
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.
The options --collapse-range, --dig-holes, --punch-hole and --zero-range are mutually exclusive.
Supported for XFS (since Linux 2.6.38), ext4 (since Linux 3.0), Btrfs (since Linux 3.7) and tmpfs (since Linux 3.5).
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.
Available since Linux 3.15 for ext4 (only for extent-based files) and XFS.
Zeroing is done within the filesystem preferably by converting the range into unwritten extents. This approach means that the specified range will not be physically 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.
:-v, --verbose <DD CLASS="c2|Enable verbose mode.:
:-V, --version <DD CLASS="c2|Display 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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