fallocate — preallocate or deallocate space to a file
−o offset ]
−l length filename
fallocate \-d [
−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.
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.
−−zero−range are mutually
Removes a byte range from a file, without leaving a
hole. The byte range to be collapsed starts at
length bytes. At the
completion of the operation, the contents of the file
starting at the location
length will be appended
at the location
offset, and the file will
smaller. The option
−−keep−size may not
be specified for colapse range operation.
Available since Linux 3.15 for ext4 (only for extent-based files) and XFS.
Detect and dig holes. This makes the file sparse
in-place, without using extra disk space. The minimum
size of the hole depends on filesystem I/O block size
(usually 4096 bytes). Also, when using this option,
implied. If no range is specified by
−−length, then the entire
file is analyzed for holes.
You can think of this option as doing a "cp --sparse" and then renaming the destination file to the original, without the need for extra disk space.
−−punch−hole for a
list of supported filesystems.
Specifies the length of the range, in bytes.
Do not modify the apparent length of the file. This may effectively allocate blocks past EOF, which can be removed with a truncate.
Specifies the beginning offset of the range, in bytes.
Deallocates space (i.e., creates a hole) in the byte
range starting at
offset and continuing for
Within the specified range, partial filesystem blocks
are zeroed, and whole filesystem blocks are removed
from the file. After a successful call, subsequent
reads from this range will return zeroes. This option
may not be specified at the same time as the
Also, when using this option,
Supported for XFS (since Linux 2.6.38), ext4 (since Linux 3.0), Btrfs (since Linux 3.7) and tmpfs (since Linux 3.5).
Enable verbose mode.
Zeroes space in the byte range starting at
length bytes. Within the
specified range, blocks are preallocated for the
regions that span the holes in the file. After a
successful call, subsequent reads from this range will
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.
−−keep−size can be
specified to prevent file length modification.
Available since Linux 3.14 for ext4 (only for extent-based files) and XFS.
Display version information and exit.
Display help text and exit.
The fallocate command is part of the util-linux package and is available from Linux Kernel Archive