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

       -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

       -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

              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
       2021-03-21.  (At that time, the date of the most recent commit
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       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)