# Open MPI v5.0.x

Open MPI is an open source implementation of the Message Passing
Interface (MPI) specification. This file indexes the LLM-friendly
documentation available for this Open MPI documentation version.

## About this file

This is a limited llms.txt for the Open MPI v5.0.x release series. It
indexes the human-facing HTML documentation and the rendered man pages.

Open MPI publishes one llms.txt per documentation version, all under the
same URL scheme:

    https://docs.open-mpi.org/en/VERSION_SLUG/llms.txt

where VERSION_SLUG is either `main` (Open MPI's development tip) or
`vA.B.C` (A and B are the major and minor version numbers; use `vA.B.x`
for a release branch, e.g. `v5.0.x`, or an exact `vA.B.C` for a
git-tagged release).

Open MPI v5.0.x publishes this limited index only. The full set of
machine-readable artifacts --- a structured JSONL API catalog, aggregate
and per-interface Markdown corpora, per-procedure Markdown pages, curated
examples and an interface guide, and a manifest --- is published for Open
MPI v6.0.0 and later. If you need that structured API data, use a v6.0.0
or later version, for example
https://docs.open-mpi.org/en/v6.0.x/llms.txt or
https://docs.open-mpi.org/en/main/llms.txt .

Documentation for Open MPI versions older than v5.0.x is not published in
this format; for those, see
https://github.com/open-mpi/ompi/blob/v4.1.x/README ,
https://www.open-mpi.org/faq/ , and https://www.open-mpi.org/doc/ .

- The MPI Standard (https://www.mpi-forum.org/docs/) is authoritative for
  portable MPI semantics.
- `MPIX_*` and `OMPI_*` APIs are Open MPI extensions, not portable MPI
  Standard APIs.

## API and command reference (man pages)

- [MPI API man pages (man3 index)](man-openmpi/man3/index.html)
- [Open MPI command man pages (man1 index)](man-openmpi/man1/index.html)

## Human-facing documentation

- [Building MPI applications](building-apps/index.html)
- [Launching MPI applications](launching-apps/index.html)
- [Tuning MPI applications](tuning-apps/index.html)

## Runtime introspection (installed Open MPI)

The links above are static documentation for this version. To inspect a
*specific* installation --- its exact Open MPI version, build
configuration, the MCA components that were compiled in, and the
run-time tunables (MCA parameters) those components expose --- query the
installation directly with the `ompi_info` command (listed in the man1
index above). That information is installation-specific, so it is not
captured here.

Version and configuration:

- `ompi_info --version` prints the Open MPI version.
- `ompi_info` with no arguments prints a human-readable summary: the
  version, the `./configure` command line, the compilers used, the
  enabled MPI language bindings, and the MCA components that were built.
- `ompi_info --parsable` prints the same information in a stable,
  machine-readable `key:value` format (for example, an
  `ompi:version:full:...` line carries the exact version).

Discovering MCA parameters: the available set depends on which
components were built, so list them from the installation with

    ompi_info --all --parsable

`--all` shows all configuration options and raises the MCA-parameter
detail to the maximum (every "level", 1--9); by default only level-1
parameters are shown. The output is self-describing: each parameter
emits one line per field, keyed
`mca:<framework>:<component>:param:<name>:<field>:<value>`, for example:

    mca:btl:tcp:param:btl_tcp_if_include:value:
    mca:btl:tcp:param:btl_tcp_if_include:level:1
    mca:btl:tcp:param:btl_tcp_if_include:help:Comma-delimited list ...
    mca:btl:tcp:param:btl_tcp_if_include:type:string

Read the field names directly from the output: typical fields are the
current `value`, its `source`, whether it is read-only (`status`), the
verbosity `level`, the `help` text, the value `type`, whether it is
`deprecated`, any `enumerator` values, and any `synonym_of` (an older
name that still works).

Setting MCA parameters: once you know a parameter's name, set it
(highest precedence first) on the `mpirun` / `mpiexec` command line, in
the environment, or in a parameter file:

    # command line (highest precedence):
    mpirun --mca btl tcp,self,sm -np 4 ./my_app

    # environment variable (prefix the parameter name with OMPI_MCA_):
    export OMPI_MCA_btl=tcp,self,sm

    # parameter file: one "name = value" per line in
    #   $HOME/.openmpi/mca-params.conf       (per user) or
    #   $prefix/etc/openmpi-mca-params.conf  (system-wide)

PMIx and PRRTE (Open MPI's run-time dependencies) have their own MCA
systems, set with the `--pmixmca` / `--prtemca` options and the
`PMIX_MCA_` / `PRTE_MCA_` environment-variable prefixes (note the single
"R" in `PRTE_MCA_`).