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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | AUTHORS | SEE ALSO | AVAILABILITY | COLOPHON |
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FALLOCATE(1) User Commands FALLOCATE(1)
fallocate - preallocate or deallocate space to a file
fallocate [-c|-p|-z] [-o offset] -l length [-n] filename
fallocate -d [-o offset] [-l length] filename
fallocate -x [-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 zeroes.
The exit status 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.
-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 collapse-
range operation.
Available since Linux 3.15 for ext4 (only for extent-based
files) and XFS.
A filesystem may place limitations on the granularity of
the operation, in order to ensure efficient
implementation. Typically, offset and len must be a
multiple of the filesystem logical block size, which
varies according to the filesystem type and configuration.
If a filesystem has such a requirement, the operation will
fail with the error EINVAL if this requirement is
violated.
-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 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.
-i, --insert-range
Insert a hole of length bytes from offset, shifting
existing data.
-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 truncate.
-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), tmpfs (since Linux 3.5) and
gfs2 (since Linux 4.16).
-v, --verbose
Enable verbose mode.
-x, --posix
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.
-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 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, --version
Display version information and exit.
-h, --help
Display help text and exit.
Eric Sandeen ⟨sandeen@redhat.com⟩
Karel Zak ⟨kzak@redhat.com⟩
truncate(1), fallocate(2), posix_fallocate(3)
The fallocate command is part of the util-linux package and is
available from Linux Kernel Archive
⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩.
This page is part of the util-linux (a random collection of Linux
utilities) project. Information about the project can be found
at ⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩. If you
have a bug report for this manual page, send it to
util-linux@vger.kernel.org. This page was obtained from the
project's upstream Git repository
⟨git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git⟩ on
2020-12-18. (At that time, the date of the most recent commit
that was found in the repository was 2020-12-17.) If you
discover any rendering problems in this HTML version of the page,
or you believe there is a better or more up-to-date source for
the page, or you have corrections or improvements to the
information in this COLOPHON (which is not part of the original
manual page), send a mail to man-pages@man7.org
util-linux April 2014 FALLOCATE(1)
Pages that refer to this page: fallocate(2), posix_fallocate(3), swapon(8)
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