fallocate - preallocate or deallocate space to a file
] -l length filename
-d [-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 zeros.
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.
- -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
- 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).
- -d, --dig-holes
- Detect and dig holes. Makes the file sparse in-place, without using extra
disk space. The minimal 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 all file is analyzed for holes.
You can think of this as doing a " cp --sparse" and
renaming the dest file as the original, without the need for extra disk
See --punch-hole for list of the supported filesystems.
- -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 colapse range operation.
Available since Linux 3.15 for ext4 (only for extent-based files) and
- -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
- -o, --offset offset
- Specifies the beginning offset of the range, in bytes.
- -l, --length length
- Specifies the length of the range, in bytes.
- -h, --help
- Display help text and exit.
- -v, --verbose
- Enable verbose mode.
- -V, --version
- Display version information and exit.
The fallocate command is part of the util-linux package and is available from