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 zeroes.
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.
Removes a byte range from a file, without leaving a hole. The
byte range to be collapsed starts at offset and continues for
length bytes. At the completion of the operation, the
contents of the file starting at the location offset+length
will be appended at the location offset, and the file will be
length bytes smaller. The option --keep-size may not be
specified for the collapse-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, --keep-size is implied. If no
range is specified by --offset and --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.
See --punch-hole for a list of supported filesystems.
Insert a hole of length bytes from offset, shifting existing
-l, --length length
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.
-o, --offset offset
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 length bytes. 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 --zero-range option. Also, when using this option,
--keep-size is implied.
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.
Enable POSIX operation mode. In that mode allocation operation
always completes, but it may take longer time when fast
allocation is not supported by the underlying filesystem.
Zeroes space in the byte range starting at offset and
continuing for 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 return zeroes.
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
Option --keep-size can be specified to prevent file length
Available since Linux 3.14 for ext4 (only for extent-based
files) and XFS.
Display version information and exit.
Display help text and exit.
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util-linux April 2014 FALLOCATE(1)