fallocate - preallocate or deallocate space to a file
] [-o offset
] [-l length
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.
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
are mutually exclusive.
- -c, --collapse-range
- 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
Available since Linux 3.15 for ext4 (only for extent-based files) and
- -d, --dig-holes
- 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
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.
- -l, --length length
- Specifies the length of the range, in bytes.
- -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
- -o, --offset offset
- Specifies the beginning offset of the range, in bytes.
- -p, --punch-hole
- 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).
- -v, --verbose
- Enable verbose mode.
- -z, --zero-range
- 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
Option --keep-size can be specified to prevent file length
Available since Linux 3.14 for ext4 (only for extent-based files) and
- -V, --version
- Display version information and exit.
- -h, --help
- Display help text and exit.
The fallocate command is part of the util-linux package and is available from