The following text is taken directly from the Open MPI README file on the Subversion development trunk.
Open MPI Version Numbers and Binary Compatibility
Open MPI has two sets of version numbers that are likely of interest
to end users / system administrator:
* Software version number
* Shared library version numbers
Both are described below, followed by a discussion of application
binary interface (ABI) compatibility implications.
Software Version Number
Open MPI's version numbers are the union of several different values:
major, minor, release, and an optional quantifier.
* Major: The major number is the first integer in the version string
(e.g., v1.2.3). Changes in the major number typically indicate a
significant change in the code base and/or end-user
functionality. The major number is always included in the version
* Minor: The minor number is the second integer in the version
string (e.g., v1.2.3). Changes in the minor number typically
indicate a incremental change in the code base and/or end-user
functionality. The minor number is always included in the version
number. Starting with Open MPI v1.3.0, the minor release number
took on additional significance (see this wiki page for more
o Even minor release numbers are part of "super-stable"
release series (e.g., v1.4.0). Releases in super stable series
are well-tested, time-tested, and mature. Such releases are
recomended for production sites. Changes between subsequent
releases in super stable series are expected to be fairly small.
o Odd minor release numbers are part of "feature" release
series (e.g., 1.3.7). Releases in feature releases are
well-tested, but they are not necessarily time-tested or as
mature as super stable releases. Changes between subsequent
releases in feature series may be large.
* Release: The release number is the third integer in the version
string (e.g., v1.2.3). Changes in the release number typically
indicate a bug fix in the code base and/or end-user
functionality. If the release number is 0, it is omitted from the
version number (e.g., v1.2 has a release number of 0).
* Quantifier: Open MPI version numbers sometimes have an arbitrary
string affixed to the end of the version number. Common strings
o aX: Indicates an alpha release. X is an integer indicating
the number of the alpha release (e.g., v1.2.3a5 indicates the
5th alpha release of version 1.2.3).
o bX: Indicates a beta release. X is an integer indicating
the number of the beta release (e.g., v1.2.3b3 indicates the 3rd
beta release of version 1.2.3).
o rcX: Indicates a release candidate. X is an integer
indicating the number of the release candidate (e.g., v1.2.3rc4
indicates the 4th release candidate of version 1.2.3).
o rV or hgV: Indicates the Subversion / Mercurial repository
number string that the release was made from (V is usually an
integer for Subversion releases and usually a string for
Mercurial releases). Although all official Open MPI releases are
tied to a single, specific Subversion or Mercurial repository
number (which can be obtained from the ompi_info command), only
some releases have the Subversion / Mercurial repository number
in the version number. Development snapshot tarballs, for
example, have the Subversion repository included in the version
to reflect that they are a development snapshot of an upcoming
release (e.g., v1.2.3r1234 indicates a development snapshot of
version 1.2.3 corresponding to Subversion repository number
Quantifiers may be mixed together -- for example v1.2.3rc7r2345
indicates a development snapshot of an upcoming 7th release
candidate for version 1.2.3 corresponding to Subversion repository
Shared Library Version Number
Open MPI started using the GNU Libtool shared library versioning
scheme with the release of v1.3.2.
NOTE: Only official releases of Open MPI adhere to this versioning
scheme. "Beta" releases, release candidates, and nightly
tarballs, developer snapshots, and Subversion/Mercurial snapshot
tarballs likely will all have arbitrary/meaningless shared
library version numbers.
For deep voodoo technical reasons, only the MPI API libraries were
versioned until Open MPI v1.5 was released (i.e., libmpi*so --
libopen-rte.so or libopen-pal.so were not versioned until v1.5).
Please see https://svn.open-mpi.org/trac/ompi/ticket/2092 for more
NOTE: This policy change will cause an ABI incompatibility between MPI
applications compiled/linked against the Open MPI v1.4 series;
such applications will not be able to upgrade to the Open MPI
v1.5 series without re-linking. Sorry folks!
The GNU Libtool official documentation details how the versioning
scheme works. The quick version is that the shared library versions
are a triple of integers: (current,revision,age), or "c:r:a". This
triple is not related to the Open MPI software version number. There
are six simple rules for updating the values (taken almost verbatim
from the Libtool docs):
1. Start with version information of "0:0:0" for each shared library.
2. Update the version information only immediately before a public
release of your software. More frequent updates are unnecessary,
and only guarantee that the current interface number gets larger
3. If the library source code has changed at all since the last
update, then increment revision ("c:r:a" becomes "c:r+1:a").
4. If any interfaces have been added, removed, or changed since the
last update, increment current, and set revision to 0.
5. If any interfaces have been added since the last public release,
then increment age.
6. If any interfaces have been removed since the last public release,
then set age to 0.
Here's how we apply those rules specifically to Open MPI:
1. The above rules do not apply to MCA components (a.k.a. "plugins");
MCA component .so versions stay unspecified.
2. The above rules apply exactly as written to the following
libraries starting with Open MPI version v1.5 (prior to v1.5,
libopen-pal and libopen-rte were still at 0:0:0 for reasons
discussed in bug ticket #2092
3. The following libraries use a slightly modified version of the
above rules: rules 4, 5, and 6 only apply to the official MPI
interfaces (functions, global variables). The rationale for this
decision is that the vast majority of our users only care about
the official/public MPI interfaces; we therefore want the .so
version number to reflect only changes to the official MPI API.
Put simply: non-MPI API / internal changes to the
MPI-application-facing libraries are irrelevant to pure MPI
4. Note, however, that libmpi.so can have its "revision" number
incremented if libopen-rte or libopen-pal change (because these
two libraries are wholly included in libmpi.so). Specifically:
the revision will change, but since we have defined that the only
relevant API interface in libmpi.so is the official MPI API,
updates to libopen-rte and libopen-pal do not change the "current"
or "age" numbers of libmpi.so.
Application Binary Interface (ABI) Compatibility
Open MPI provided forward application binary interface (ABI)
compatibility for MPI applications starting with v1.3.2. Prior to
that version, no ABI guarantees were provided.
Starting with v1.3.2, Open MPI provides forward ABI compatibility in
all versions of a given feature release series and its corresponding
super stable series. For example, on a single platform, an MPI
application linked against Open MPI v1.7.2 shared libraries can be
updated to point to the shared libraries in any successive v1.7.x or
v1.8 release and still work properly (e.g., via the LD_LIBRARY_PATH
environment variable or other operating system mechanism).
* A bug that causes an ABI compatibility issue was discovered after
v1.7.3 was released. The bug only affects users who configure their
Fortran compilers to use "large" INTEGERs by default, but still have
"normal" ints for C (e.g., 8 byte Fortran INTEGERs and 4 byte C
ints). In this case, the Fortran MPI_STATUS_SIZE value was computed
Fixing this issue breakes ABI *only in the sizeof(INTEGER) !=
sizeof(int) case*. However, since Open MPI provides ABI guarantees
for the v1.7/v1.8 series, this bug is only fixed if Open MPI is
configured with the --enable-abi-breaking-fortran-status-i8-fix
flag, which, as its name implies, breaks ABI. For example:
shell$ ./configure --enable-abi-breaking-fortran-status-i8-fix \
CC=icc F77=ifort FC=ifort CXX=icpc \
FFLAGS=i8 FCFLAGS=-i8 ...
* A second bug was discovered after v1.7.3 was released that causes
ABI to be broken for gfortran users who are using the "mpi" Fortran
module. In short, for versions of gfortran that do not support
"ignore TKR" functionality (i.e., gfortran <=v4.8), Open MPI was
providing interfaces for MPI subroutines with choice buffers (e.g.,
MPI_Send) in the Fortran mpi module. The MPI-3.0 specification
expressly states not to do this. To be consistent with MPI-3, Open
MPI v1.7.4 therefore removed all MPI interfaces with choice buffers
from the no-ignore-TKR version of the Fortran mpi module, even
though this breaks ABI between v1.7.3 and v1.7.4. Affected users
should be able to recompile their MPI applications with v1.7.4 with
Other Fortran compilers that provide "ignore TKR" functionality are
not affected by this change.
Open MPI reserves the right to break ABI compatibility at new feature
release series. For example, the same MPI application from above
(linked against Open MPI v1.7.2 shared libraries) will likely *not*
work with Open MPI v1.9 shared libraries.