fallocate(1) — Linux manual page


FALLOCATE(1)                    User Commands                   FALLOCATE(1)

NAME         top

       fallocate - preallocate or deallocate space to a file

SYNOPSIS         top

       fallocate [-c|-p|-z] [-o offset] -l length [-n] filename

       fallocate -d [-o offset] [-l length] filename

       fallocate -x [-o offset] -l length filename

DESCRIPTION         top

       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

OPTIONS         top

       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

       -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

              Option --keep-size can be specified to prevent file length

              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.

AUTHORS         top

       Eric Sandeen ⟨sandeen@redhat.com⟩
       Karel Zak ⟨kzak@redhat.com⟩

SEE ALSO         top

       truncate(1), fallocate(2), posix_fallocate(3)

AVAILABILITY         top

       The fallocate command is part of the util-linux package and is
       available from Linux Kernel Archive 

COLOPHON         top

       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
       2020-08-13.  (At that time, the date of the most recent commit that
       was found in the repository was 2020-08-12.)  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

util-linux                       April 2014                     FALLOCATE(1)

Pages that refer to this page: fallocate(2)posix_fallocate(3)swapoff(8)swapon(8)