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(2) 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 length 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

       -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.

       -h, --help
           Display help text and exit.

       -V, --version
           Print version and exit.

AUTHORS         top

       Eric Sandeen <sandeen@redhat.com>, Karel Zak <kzak@redhat.com>

SEE ALSO         top

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

REPORTING BUGS         top

       For bug reports, use the issue tracker at

AVAILABILITY         top

       The fallocate command is part of the util-linux package which can
       be downloaded 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
       2024-06-14. (At that time, the date of the most recent commit
       that was found in the repository was 2024-06-10.) 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 2.39.594-1e0ad      2023-07-19                   FALLOCATE(1)

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