Open MPI v5.0.x series
======================

This file contains all the NEWS updates for the Open MPI v5.0.x
series, in reverse chronological order.

Open MPI Version v5.0.10rc2
------------------------------
:Date: 11 February 2026

- Internal PMIx and PRRTe versions:
  - PMIx (v5.0.10). Repo: ``https://github.com/openpmix/openpmix``. Commit hash: ``52275072f255ce0b94bd714e0e83f6a34d471c51``.
  - PRRTE (v3.0.13). Repo: ``https://github.com/openpmix/prrte``. Commit hash: ``643db1bd3d53bb44bd5afc1dc40e3786f7da9009``.

- OSHMEM Enhancements
  - OSHMEM/SPML/UCX: Implemented put_signal and put_signal_nbi operations for OpenSHMEM 1.5 compliance
  - OSHMEM/SHMEM/C: Added shmem_signal_fetch implementation
  - OSHMEM/ATOMIC/UCX: Added UCX version check for non-blocking atomics value packing

- OFI (libfabric) Improvements
  - BTL/OFI: Added fault tolerance support
  - BTL/OFI: Set domain threading model based on MPI thread support level
  - BTL/OFI: Added FI_COMPLETION flag to tx and rx attributes
  - BTL/OFI: Check for valid pointer in error handler to prevent crashes
  - OFI: Share domain between MTL and BTL components for better resource utilization

- Fault Tolerance (ULFM) Enhancements
  - Revoke: Fixed null dereference and improved debug prints
  - Revoke: Centralized entrypoint for locally revoking a communicator
  - Revoke: Fixed coll/han subcomms revocation
  - Removed era_comm_free function and documented reasoning (prevents use-after-free with revoke)
  - Communicators: Prevent subcomms from being freed before user's communicator
  - Communicators: Always populate failed procs in comms' groups
  - Communicators: Retain coll info when adding a callback to the event queue

- Bug Fixes and Minor Enhancements
  - PML/UCX: Fixed problem with MPI_Mrecv and MPI_Imrecv operations
  - PML/OB1: Moved sendreq 'error after freed' check to correct location
  - BTL: Fixed ompi_info display for btl_flags enumeration
  - BTL/SM: Fixed wrong payload_buffer size during freelist initialization
  - COLL/UCC: Fixed indentation issues and prevented SEGV on error handling
  - SHAREDFP/LOCKEDFILE: Removed filename length limitation
  - OPAL/COMMON/UCX: Fixed assert - changed thread mode sent to UCX API
  - OPAL: Fixed logic error in opal_bitmap.c array length calculation
  - Fortran: Create Fortran module directory if it doesn't exist
  - Fortran: mpi_f08/request_get_status: removed invalid fast-path that returned flag=false for MPI_STATUS_IGNORE when operation was completed (fixes #13671)
  - I/O: Fixed inverted collective_buffering hint logic (strncmp misuse: 'true' was disabling, 'false' enabling)
  - Documentation: Updated TCP tuning page
  - Documentation: Added notes that some functions currently require mpirun
  - Documentation: Fixed typo in mpicc manpage
  - Build system: Fixed code scanning alerts (security issues 1-7, 12, 17-19, 21-22)
  - Build system: Fixed typos throughout the codebase
  - Build system: Properly support git workspaces in update-my-copyright.py script
  - GitHub Actions: Updated permissions for better security
  - CI: Commented out hello_sessions_c test in macOS workflow
  - CI: ompi_nvidia – add concurrency queue to serialize PR runs and avoid pod collisions
  - CI: Trufflehog – add allowlist for libevent test private key false positive

Open MPI Version v5.0.9
------------------------------
:Date: 30 October 2025

- Internal PMIx and PRRTe versions:
  - PMIx (v5.0.9). Repo: ``https://github.com/openpmix/openpmix``. Commit hash: ``b357357c09915779eabd362f6857f61b41680329``.
  - PRRTE (v3.0.12). Repo: ``https://github.com/openpmix/prrte``. Commit hash: ``b357357c09915779eabd362f6857f61b41680329``.

- Functionality Enhancements
  - GPFS: Added support for GPFS 5.2.3-0 and newer versions
  - OFI: Enhanced accelerator memory support with proper rcache flag handling
  - OFI: Added memory monitor export for better memory management
  - ROCm: Added missing header for memcpy operations in accelerator component
  - UCC: Set node local id for better collective operation performance
  - UCX: Set node local id in PML component for improved communication

- Bug Fixes and Minor Enhancements
  - PML OB1: Fixed critical bug in MCA_PML_OB1_ADD_ACK_TO_PENDING that could cause memory overruns or allocation failures
  - CUDA: Fixed CUDA detection when multiple libcuda.so files exist in CUDA install directory
  - Fortran: Fixed off-by-one string copy error in C2F string conversion
  - Fortran: Fixed ompi string c2f conversion when Fortran string length is less than C string length
  - Threading: Fixed OMPI_MPI_THREAD_LEVEL environment variable handling to allow useful overrides in threaded library use cases
  - Threading: Enhanced OMPI_MPI_THREAD_LEVEL to accept both numeric (0-3) and string ('multiple', 'MPI_THREAD_MULTIPLE', etc.) values
  - OSC: Fixed rdma component when not using ob1 PML
  - S390x: Fixed alignment of opal_atomic_int128_t to be 16-byte aligned
  - Configury: Improved Fortran complex(real16) testing and module file cleanup
  - Documentation: Fixed MCA environment variable prefix documentation for PRRTE
  - Documentation: Updated MPI_Init*/MPI_Finalize*/MPI_Session_* man pages with numerous improvements
  - Build system: Removed whitespace from conftestval-style tests and cleaned up configuration

Open MPI Version v5.0.8
------------------------------
:Date: 30 May 2025

- Internal PMIx and PRRTe versions:
  - PMIx (v5.0.8). Repo: ``https://github.com/openpmix/openpmix``. Commit hash: ``907b1ccaeec61a1197f0ee5264d4fef20b257b84``.
  - PRRTE (v3.0.11). Repo: ``https://github.com/openpmix/prrte``. Commit hash: ``222f03fbb98b71abd293aa205b38fa9a38e57965``.

- Functionality Enhancements
  - UCC collective operations: Improved handling of MPI_IN_PLACE in allgather, allgatherv, alltoall, alltoallv, gather, gatherv, scatter, and scatterv operations
  - UCX OSC: Added support for "no_locks" info key to disable lock table usage
  - OFI MTL: Enhanced CXI provider support for better compatibility
  - AARCH64: Added SVE detection alongside NEON in aarch64 op component
  - Fortran: Fixed common symbol sizes and alignments for better compatibility

- Bug Fixes and Minor Enhancements
  - Hugepage Mpool: Fixed sizing of hugepages for better memory management
  - Configure: Fixed --with-prrte=internal option handling
  - Documentation: Updated shared memory and networking documentation
  - Build system: Fixed support for flang on OSX
  - Removed unused spread contrib sample scripts
  - Various documentation updates and improvements
  - CI: Removed Ubuntu 18 and RHEL 7 from test matrix
  - Fixed type mismatch errors in shared memory components
  - Updated Java configuration for latest Fedora releases
  - Fixed memory zone reference counting in UCX dynamic windows

Open MPI Version v5.0.7
------------------------------
:Date: 14 February January 2025

- Internal PMIx and PRRTe version:
  - PMIx (v5.0.5). Repo: ``https://github.com/openpmix/openpmix``. Commit hash: ``707920c99de946a5c3a1850da457340f38c0caf2``.
  - PRRTE (v3.0.8). repo: ``https://github.com/openpmix/prrte``. Commit hash: ``f6f5c181c1dec317c31f61effd73f960ce2eac25``.

- Updated UCX version requirement to v1.9

- Documentation Improvements
  - Updated `coll tuned` rules file documentation to reflect changes in versioning and features.
  - Updated CUDA-related networking documentation for consistency.
  - Improved descriptions for `mpirun` options, including ``--pmixmca`` and ``--prtemca``.
  - Fixed typos and formatting issues in `mpirun` man pages.

- Functionality Enhancements
  - Improved argument checking for ``MPI_Comm_create_from_group`` and ``MPI_Intercomm_create_from_groups`` to align with MPI 4.0 standards.
  - Addressed potential race conditions in `PMIx_Group_construct` calls by adding discriminators.
  - Fixed ``MPI_Wtime`` to initialize timing relative to ``MPI_Init`` for accurate session-level measurements.
  - Added support for the `alltoall_algorithm_max_requests` parameter in the `coll tuned` rules file, maintaining backward compatibility.
  - Introduced a version identifier for the `coll tuned` rules file for better parser handling.
  - Adjusted MCA variable scopes across multiple components to allow setting via the `MPI_T` interface: `coll adapt,ucc, han, basic, hcoll`

- Bug Fixes and Minor Enhancements
  - Ensures that singletons properly create their own sessions directory trees.
  - Fixed community Jenkins build pipeline to handle branch commits properly.
  - Resolved missing profiling symbols in the `mpi_f08` Fortran library.
  - Corrected parameter mismatches in `coll/cuda` functions to avoid type issues.
  - Fixed build issues on Hurd.
  - Removed unused portions of rcache base structure.
  - Fixed oshmem base segment address exchange.
  - Fixed UCC collective fallback issue.
  - Updated Nvidia/Mellanox platform file

Open MPI Version v5.0.6
------------------------------
:Date: 14 November 2024

- Internal PMIx and PRRTe version:

  - PMIx (v5.0.4). Repo: ``https://github.com/openpmix/openpmix``. Commit hash: ``20ad9b16fe49ede4a76e7489bdf0e2ea05c3de95``.
  - PRRTE (v3.0.7). repo: ``https://github.com/openpmix/prrte``. Commit hash: ``b2f4163e40a84fe777fa36dfbffa4db23d8d31dd``.

  - Session Management Enhancements:
  - Finalization Control: Ensures proper finalization of classes when references to the OPAL utility layer reach zero. A new smoke test has been added to validate this behavior.
  - Test and CI Additions: A smoke test was introduced for session management, also integrated into macOS GitHub CI to ensure stability across platforms.
  - Recognize requests from the same instance rather than same communicator, fixes Waitall/Waitany/Testall/Testany.
  - Multiple Init/Finalize Handling: Improvements to handling session multiple initializations and finalizations, addressing issues with parameter management and session destruction.

  - CUDA and NVIDIA HPC Compiler Compatibility:
  - Stream-ordered Allocations: Adjustments for handling CUDA stream-ordered allocations and assigning primary device context in `opal/cuda` (Akshay Venkatesh).
  - nvfortran Compatibility: Configure script updated to handle NVIDIA's `nvfortran` compiler, enabling proper compilation with `-fPIC` flags for shared libraries (Gilles Gouaillardet).
  - CUDA Memory Address Management: Improvements for handling virtual memory manager (VMM) pointers in CUDA applications to prevent runtime issues.

  - MPI Communication and Resource Management:
  - Info Duplication: Enhanced `MPI_Info_dup` function to ensure consistent key management across duplicated info objects, supporting better memory and resource handling.
  - OFI/Initialization Improvements: Refactored code for OFI common components to support session-based initialization models per MPI 4 standards.
  - Resource Leak Fixes: Addressed memory leaks and reference count issues in several components to improve memory management and stability in high-demand environments.

  - Detailed Locking Protocol: Modified default file-locking protocols in UFS component to ensure data consistency, especially when using data-sieving operations, which require broader locking.

  - MPI_T Interface Enhancements: Modified MCA parameter settings to allow runtime tuning of collectives through the MPI_T interface, adding flexibility for dynamic rules in collective operations.
  - Corrected various documentation typos and clarified parameter settings in several API references, improving readability and usability for end users.

Open MPI version v5.0.5
--------------------------
:Date: 23 July 2024

  .. note:: This is a quick follow-up release that fixes v5.0.4 which does
            not compile on macOS (arm64) with the inbox Apple clang compiler (``/usr/bin/gcc``).
            The *only* change in v5.0.5 compared to v5.0.4 is a fix for this compilation issue.

- Internal PMIx and PRRTe versions:

  - PMIx (v5.0.3). Commit hash: ``8ab6d680b90afd6e61766220a8724065a1b554a7``.
  - PRRTE (v3.0.6). Commit hash: ``b68a0acb32cfc0d3c19249e5514820555bcf438b``.

- Bugfixes and changes

  - Fix a typo that breaks the build on macOS with the Apple clang compiler on arm64 platforms.
    Many thanks to Lisandro Dalcin for reporting the issue.

Open MPI version v5.0.4
--------------------------
:Date: 19 July 2024

- Internal PMIx and PRRTe versions:

  - PMIx (v5.0.3). Commit hash: ``8ab6d680b90afd6e61766220a8724065a1b554a7``.
  - PRRTE (v3.0.6). Commit hash: ``b68a0acb32cfc0d3c19249e5514820555bcf438b``.

- Bugfixes and changes

  - btl/ofi: retry posting receive buffer
  - btl/uct: check return status from some uct funcs
  - fortran: use -Wl,-ld_classic if supported
  - fortran: parameterize the install location of Fortran MPI bindings modulefiles
    via the configure --with-mpi-moduledir CLI option
  - fortran: various configury improvements
  - use-mpi-f08: add missing subroutines in the mpi_f08 module
  - pml/base: remove redundant copy of ompi_mpi_thread_multiple
  - pml/cm: release datatype object in send completion callback
  - pml/ucx: propagate MPI serialized thread mode for all worker creations
  - pml/ob1: make no. of events an mca parameter
  - oshmem/shmem: fix warnings regarding types and unused variables in shmem
  - Add an AARCH64 OP component for for NEON and SVE ISA
  - Fix MPI function names in error output
  - Fix MPI_Neighbor_alltoall{v,w}_init to handle NULL parameters
  - Fix a bug in intercomm creation
  - Fix a bug in ompi_comm_lookup function to handle partially ready communicators
  - Fix error message in ompi_comm_get_rproc
  - Fix opal_basename for single character filenames
  - Fix rpm build test
  - Fix the info subscriber mechanism and hidden info keys
  - Fix ulfm bugs in ishrink/agree/iagree
  - Improve libcuda.so find command to follow symlinks
  - Improve pkgconfig installation logic in script wrapper
  - Change default tar format to tar-pax
  - Various document updates

- Many thanks to Open MPI community including:
  Alex Margolin, Benjamin Kitor, Burlen Loring, Ethan Townsend, Geoffroy Vallee,
  Jeff Hammond, Junchao Zhang, Lisandro Dalcin, Nuno Nobre, Rainer Keller,
  Roie Danino, Thomas Vegas

Open MPI version v5.0.3
--------------------------
:Date: 9 April 2024

- Internal PMIx and PRRTe versions:

  - PMIx (v5.0.2). Commit hash: ``33e93469e1e1f69904ff3e3827394719aa6b3671``.
  - PRRTE (v3.0.5). Commit hash: ``3a70fac9a21700b31c4a9f9958afa207a627f0fa``.

- Bugfixes and changes

  - Fix HAN MPI_Scatter intra-node data count and type 
  - Add missing write memory barrier in btl/smcuda 
  - Fix MPI_Alltoallv and MPI_Ialltoallv data count and type check
  - Enhance cuda-aware build by detecting default --with-cuda-lib value
  - Enhance ofi NIC selection logic
  - Fix an illegal memory access bug in mtl/ofi
  - Multiple bugfixes in rocm accelerator 
  - Fix a double free bug in oshmem
  - Add missing oshmem headers
  - Fix uninitialized lock in btl/usnic
  - Fix uninitialized mutex in file_open
  - Fix compiler warnings about unused cid_base variable
  - Enhance autogen submodule checks
  - Various document updates

- Many thanks to Open MPI community including:
  Christoph Niethammer, Christoph van Wüllen, Jakub Klinkovský, Lisandro Dalcin

Open MPI version v5.0.2
--------------------------
:Date: 6 February 2024

- Internal PMIx and PRRTe versions:

  - PMIx (v4.2.8). Commit hash: ``d1c1ed0c2e64f19ad49291241a43630ea7fdce28``.
  - PRRTE (v3.0.3). Commit hash: ``e383f5ad70c2633420d3425e9fb67e69b6bfd9c4``.

  .. note:: Due to the timing of Open MPI v5.0.2 release, the PMIx and PRRTE versions
            that are internally bundled in the Open MPI distribution are the same
            versions as in the Open MPI v5.0.1 release: PMIx v4.2.8 and PRRTE v3.0.3.
            As a result, changes and bug fixes in newer PMIx and PRRTE releases are
            not included in Open MPI v5.0.2, notably:

            PRRTE

            - Fix the map-by pe-list option
            - Use pmix_path_nfs to detect shared file systems
            - psets: fix some problems with PMIX_QUERY_PSET_MEMBERSHIP query.
              PMIX_QUERY_PSET_MEMBERSHIP query bugfixes.

            PMIx

            - Restore default to enable-devel-check in Git repos
            - Protect against empty envar definition for mca_base_param_files
            - PMIx_Query_info: removed duplicated PMIX_RELEASE
            - Do not add no-unused-parameter for non-devel-check builds
            - Cast a few parameters when translating macros to functions
            - Fix one more spot for "get" from rank undefined
            - Fix "get" of key with undefined rank
            - Resolve problem of stack variables and realloc
            - Restore support for detecting shared file systems
            - Fix broken link in README

- Bugfixes and changes (in chronological order)

  - Fix the fs/lustre component build
  - Fix a mtl/ofi multi-threaded race condition bug
  - Add missing fortran profiling interfaces according to MPI 4.0 standard
  - Allow 0-size data copy in opal/accelerator
  - Fix a btl/ofi and mtl/ofi provider selection bug
  - Properly initialize mca_rcache_base_module_t members
  - Fix a singleton launch segfault
  - Add GCC13 support with MacOS compatibility

- Many thanks to Open MPI community including:
  Erik Schnetter 

Open MPI version v5.0.1
--------------------------
:Date: 20 December 2023

- Internal PMIx and PRRTe versions:

  - PMIx (v4.2.8). Commit hash: ``d1c1ed0c2e64f19ad49291241a43630ea7fdce28``.
  - PRRTE (v3.0.3). Commit hash: ``e383f5ad70c2633420d3425e9fb67e69b6bfd9c4``.

- Bugfixes and changes (in chronological order)

  - Various documentation related updates and changes
  - Fix a bunch of compiler warnings
  - Sessions: fix a problem with fortran MPI_Session_get_nth_pset interface
  - Correctly access the communicator name is MSGQ
  - accelerator/cuda: fix bug in makefile.am preventing correct linkage
    in non-standard location
  - btlsmcuda: fix problem with makefile
  - Fix rcache/gpusm and rcache/rgpsum
  - Correctly handle attributes on MPI_COMM_WORLD.
  - Minor memory leak fixes in:
    btl/tcp, mca_base_framework, ob1
  - Fix static initialization of recursive mutexes
  - Spack: fix for dlopen missing symbol problem
  - opal/mca/accelerator: ROCm 6.0 incompatibility fix
  - opal_var_dump_color_keys: fix an array overflow
  - SHMEM_LOCKS: MCS implementation of SHMEM LOCKS
  - configury: support flang-new
  - Update processing of "display_map" info key
  - dpm: update PMIX attribute

- Many thanks to Open MPI community including:
  Tony Curtis, David Edwards Linaro, Niv Shpak for their contribution.

Open MPI version 5.0.0
--------------------------
:Date: 25 October 2023

.. admonition:: The MPIR API has been removed
   :class: warning

   As was announced in the summer of 2017, Open MPI has removed
   support for MPIR-based tools beginning with the release of Open MPI
   v5.0.0.

   Open MPI now uses the `PRRTE <https://github.com/openpmix/prrte>`_
   runtime environment, which supports the `PMIx <https://pmix.org/>`_
   tools API |mdash| instead of the legacy MPIR API |mdash| for
   debugging parallel jobs.

   Users who still need legacy MPIR support should see
   https://github.com/hpc/mpir-to-pmix-guide for more information.

.. admonition:: Zlib is suggested for better performance
   :class: note

   `PMIx <https://pmix.org/>`_ will optionally use `Zlib
   <https://github.com/madler/zlib>`_ to compress large data streams.
   This may result in faster startup times and smaller memory
   footprints (compared to not using compression).

   The Open MPI community recommends building PMIx with Zlib support,
   regardless of whether you are using an externally-installed PMIx or
   the bundled PMIx that is included with Open MPI distribution
   tarballs.

   Note that while the Zlib library *may* be present on many systems
   by default, the Zlib header files |mdash| which are needed to build
   PMIx with Zlib support |mdash| may need to be installed separately
   before building PMIx.

.. caution:: Open MPI has changed the default behavior of how it
             builds and links against its :ref:`required 3rd-party
             packages <label-install-required-support-libraries>`:
             `Libevent <https://libevent.org/>`_, `Hardware Locality
             <https://www.open-mpi.org/projects/hwloc/>`_, `PMIx
             <https://pmix.org/>`_, and `PRRTE
             <https://github.com/openpmix/prrte>`_.

             #. Unlike previous versions of Open MPI, Open MPI 5.0 and
                later will prefer an external package that meets our
                version requirements, even if it is older than our
                internal version.
             #. To simplify managing dependencies, any required
                packages that Open MPI |ompi_series| bundles will be
                installed in Open MPI's installation prefix, without
                name mangling.

                For example, if a valid Libevent installation cannot
                be found and Open MPI therefore builds its bundled
                version, a ``libevent.so`` will be installed in Open
                MPI's installation tree. This is different from
                previous releases, where Open MPI name-mangled the
                Libevent symbols and then statically pulled the
                library into ``libmpi.so``.

- Internal PMIx and PRRTe versions:

  - PMIx release tag v4.2.7. Commit hash: ``57c405c52ad76bab0be9f95e29a6df660673081e``.
  - PRRTE release tag v3.0.2. Commit hash: ``1552e36f0852bbc6d901ec95983369f0a3c283f6``.

- All other notable updates for v5.0.0:

  - MPI-4.0 updates and additions:

    - Support for MPI Sessions has been added.
    - Added partitioned communication using persistent sends
      and persistent receives.
    - Added persistent collectives to the ``MPI_`` namespace
      (they were previously available via the ``MPIX_`` prefix).
    - Added ``MPI_Isendrecv()`` and its variants.
    - Added support for ``MPI_Comm_idup_with_info()``.
    - Added support for ``MPI_Info_get_string()``.
    - Added support for ``initial_error_handler`` and the
      ``ERRORS_ABORT`` infrastructure.
    - Added error handling for unbound errors to ``MPI_COMM_SELF``.
    - Made ``MPI_Comm_get_info()``, ``MPI_File_get_info()``, and
      ``MPI_Win_get_info()`` compliant to the standard.
    - Droped unknown/ignored info keys on communicators, files,
      and windows.
    - Initial implementations of ``MPI_COMM_TYPE_HW_GUIDED`` and
      ``MPI_COMM_TYPE_HW_GUIDED`` added.
    - ``MPI_Info_get()`` and ``MPI_Info_get_valuelen()`` are now
      deprecated.
    - Issue a deprecation warning when ``MPI_Cancel()`` is called for
      a non-blocking send request.

  - New Features:

    - ULFM Fault Tolerance support has been added. See :ref:`the ULFM
      section <ulfm-label>`.
    - CUDA is now supported in the ``ofi`` MTL.
    - A threading framework has been added to allow building Open MPI
      with different threading libraries. It currently supports
      `Argobots <https://www.argobots.org/>`_, `Qthreads
      <https://github.com/Qthreads/qthreads>`_, and Pthreads.  See the
      ``--with-threads`` option in the ``configure`` command.  Thanks
      to Shintaro Iwasaki and Jan Ciesko for their contributions to
      this effort.
    - New Thread Local Storage API: Removes global visibility of TLS
      structures and allows for dynamic TLS handling.
    - Added new ``Accelerator`` framework. CUDA-specific code
      was replaced with a generic framework that standardizes various
      device features such as copies or pointer type detection. This
      allows for modularized implementation of various devices such as
      the newly introduced ROCm Accelerator component. The redesign
      also allows for Open MPI builds to be shipped with CUDA
      support enabled without requiring CUDA libraries.
    - Added load-linked, store-conditional atomics support for
      AArch64.
    - Added atomicity support to the ``ompio`` component.
    - ``osc/rdma``: Added support for MPI minimum alignment key.
    - Add ability to detect patched memory to
      ``memory_patcher``. Thanks to Rich Welch for the contribution.
    - ``coll/ucc``: Added support for the ``MPI_Scatter()`` and
      ``MPI_Iscatter()`` collectives.
    - New algorithm for Allgather and Allgatherv has been added, based
      on the paper *"Sparbit: a new logarithmic-cost and data
      locality-aware MPI Allgather algorithm"*. Default algorithm
      selection rules are unchanged; to use these algorithms add:
      ``--mca coll_tuned_allgather_algorithm sparbit`` and/or ``--mca
      coll_tuned_allgatherv_algorithm sparbit`` to your ``mpirun``
      command.  Thanks to Wilton Jaciel Loch and Guilherme Koslovski
      for their contribution.

  - Transport updates and improvements

    - One-sided Communication:

      - Many MPI one-sided and RDMA emulation fixes for the ``tcp`` BTL.

        This patch series fixs many issues when running with ``--mca
        osc rdma --mca btl tcp``, i.e., TCP support for one sided
        MPI calls.

      - Many MPI one-sided fixes for the ``uct`` BTL.
      - Added support for ``acc_single_intrinsic`` to the one-sided
        ``ucx`` component.
      - Removed the legacy ``pt2pt`` one-sided component. Users should
        now utilize the ``rdma`` one-sided component instead.  The
        ``rdma`` component will use BTL components |mdash| such as the
        TCP BTL |mdash| to effect one-sided communications.

    - Updated the ``tcp`` BTL to use graph solving for global
      interface matching between peers in order to improve
      ``MPI_Init()`` wireup performance.

    - OFI

      - Improved support for the HPE SS11 network.
      - Added cache bypass mechanism. This fixes conflicts with
        `Libfabric <https://libfabric.org/>`_, which has its own
        registration cache. This adds a bypass flag which can be used
        for providers known to have their own registration cache.

    - Shared Memory:

      - Update the new ``sm`` BTL to not use Linux Cross Memory Attach
        (CMA) in user namespaces.
      - Fixed a crash when using the new ``sm`` BTL when compiled with
        Linux Cross Memory Attach (``XPMEM``).  Thanks to George
        Katevenis for reporting this issue.

    - Updated the ``-mca pml`` option to only accept one PML, not a list.

  - Deprecations and removals:

    - The legacy ``sm`` (shared memory) BTL has been removed.  The
      next-generation shared memory BTL ``vader`` replaces it, and
      has been renamed to be ``sm`` (``vader`` will still work as an
      alias).
    - ORTE, the underlying Open MPI launcher has been removed, and
      replaced with the `PMIx Reference RunTime Environment
      <https://github.com/openpmix/prrte>`_ (``PRTE``).
    - PMI support has been removed from Open MPI; now only PMIx is
      supported.  Thanks to Zach Osman for contributing.
    - The following components have been removed, and are replaced by
      UCX support: PML ``yalla``, PML ``mxm``, SPML ``ikrit``.
    - The MTL ``psm`` component has been removed and is no longer
      supported.
    - Removed all vestiges of Checkpoint Restart (C/R) support.
    - 32 bit atomics are now only supported via C11 compliant compilers.
    - Explicitly disable support for GNU gcc < v4.8.1 (note: the
      default gcc compiler that is included in RHEL 7 is v4.8.5).
    - Various atomics support removed: S390/s390x, Sparc v9, ARMv4 and
      ARMv5 with CMA support.
    - The MPI C++ bindings have been removed.
    - The ``mpirun`` options ``--am`` and ``--amca`` options have been
      deprecated.
    - The ``libompitrace`` contributed library has been removed.
      This library was incomplete and unmaintained. If needed, it
      is available in the v4.x series.
    - The rankfile format no longer supports physical processor
      locations. Only logical processor locations are supported.
    - 32-bit builds have been disabled. Building Open MPI in a 32-bit
      environment is no longer supported.  32 bit support is still
      available in the v4.x series.

  - Other updates and bug fixes:

    - Updated Open MPI to use ``ROMIO`` v3.4.1.
    - Add missing ``MPI_Status`` conversion subroutines:
      ``MPI_Status_c2f08()``, ``MPI_Status_f082c()``,
      ``MPI_Status_f082f()``, ``MPI_Status_f2f08()`` and the
      ``PMPI_*`` related subroutines.
    - MPI module: added the ``mpi_f08`` ``TYPE(MPI_*)`` types for
      Fortran.  Thanks to George Katevenis for the report and their
      contribution to the patch.
    - The default atomics have been changed to be GCC, with C11 as a
      fallback. C11 atomics incurs sequential memory ordering, which
      in most cases is not desired.
    - The default build mode has changed from building Open MPI's
      components as Dynamic Shared Objects (DSOs) to being statically
      included in their respective libraries.

      .. important:: This has consequences for packagers.  Be sure to
                     read the :ref:`GNU Libtool dependency flattening
                     <label-install-packagers-gnu-libtool-dependency-flattening>`
                     subsection.

    - Various datatype bugfixes and performance improvements.
    - Various pack/unpack bugfixes and performance improvements.
    - Various OSHMEM bugfixes and performance improvements.
    - Thanks to Jeff Hammond, Pak Lui, Felix Uhl, Naribayashi Akira,
      Julien Emmanuel, and Yaz Saito for their invaluable contributions.

  - Documentation updates and improvements:

    - Open MPI has consolidated and converted all of its documentation
      to use `ReStructured Text.
      <https://www.sphinx-doc.org/en/master/usage/restructuredtext/basics.html>`_
      and `Sphinx <https://www.sphinx-doc.org/>`_.

      - The resulting documentation is now hosted on
        https://docs.open-mpi.org (via `ReadTheDocs
        <https://ReadTheDocs.io/>`_).
      - The documentation is also wholly available offline via Open
        MPI distribution tarballs, in the ``docs/_build/html``
        directory.

    - Many, many people from the Open MPI community contributed to the
      overall documentation effort |mdash| not just those who are
      listed in the Git commit logs.  Indeed, many Open MPI core
      developers contributed their time and effort, as did a fairly
      large group of non-core developers (e.g., those who participated
      just to help the documentation revamp), including (but not
      limited to):

      - Lachlan Bell
      - Simon Byrne
      - Samuel Cho
      - Tony Curtis
      - Lisandro Dalcin
      - Sophia Fang
      - Rick Gleitz
      - Colton Kammes
      - Robert Langfield
      - Nick Papior
      - Luz Paz
      - Alex Ross
      - Hao Tong
      - Mitchell Topaloglu
      - Siyu Wu
      - Fangcong Yin
      - Seth Zegelstein
      - Yixin Zhang
