Note that in both models, invoking mpirun via an absolute path
name is equivalent to specifying the --prefix option with a
<dir> value equivalent to the directory where mpirun
resides, minus its last subdirectory. For example:
% /usr/local/bin/mpirun ...
is equivalent to
% mpirun --prefix /usr/local
If you are simply looking for how to run an MPI application, you
probably want to use a command line of the following form:
This will run X copies of <program> in your current run-time
environment (if running under a supported resource manager, Open MPI's
mpirun will usually automatically use the corresponding resource manager
process starter, as opposed to, for example, rsh or ssh,
which require the use of a hostfile, or will default to running all X
copies on the localhost), scheduling (by default) in a round-robin fashion by
CPU slot. See the rest of this page for more details.
will send the name of the directory where it was invoked on the local
node to each of the remote nodes, and attempt to change to that
directory. See the "Current Working Directory" section below for further
The program executable. This is identified as the first non-recognized argument
Pass these run-time arguments to every new process. These must always
be the last arguments to mpirun. If an app context file is used,
<args> will be ignored.
Display help for this command
Suppress informative messages from orterun during application execution.
Print version number. If no other arguments are given, this will also
cause orterun to exit.
To specify which hosts (nodes) of the cluster to run on:
-H, -host, --host <host1,host2,...,hostN>
List of hosts on which to invoke processes.
-hostfile, --hostfile <hostfile>
Provide a hostfile to use.
-machinefile, --machinefile <machinefile>
Synonym for -hostfile.
To specify the number of processes to launch:
-c, -n, --n, -np <#>
Run this many copies of the program on the given nodes. This option
indicates that the specified file is an executable program and not an
application context. If no value is provided for the number of copies to
execute (i.e., neither the "-np" nor its synonyms are provided on the command
line), Open MPI will automatically execute a copy of the program on
each process slot (see below for description of a "process slot"). This
feature, however, can only be used in the SPMD model and will return an
error (without beginning execution of the application) otherwise.
-npersocket, --npersocket <#persocket>
On each node, launch this many processes times the number of processor
sockets on the node.
The -npersocket option also turns on the -bind-to-socket option.
-npernode, --npernode <#pernode>
On each node, launch this many processes.
On each node, launch one process -- equivalent to -npernode 1.
To map processes to nodes:
Uniform distribution of ranks across all nodes. See more detailed description below.
Do not run any copies of the launched application on the same node as
orterun is running. This option will override listing the localhost
with --host or any other host-specifying mechanism.
Do not oversubscribe any nodes; error (without starting any processes)
if the requested number of processes would cause oversubscription.
This option implicitly sets "max_slots" equal to the "slots" value for
Launch processes one per node, cycling by node in a round-robin
fashion. This spreads processes evenly among nodes and assigns
ranks in a round-robin, "by node" manner.
For process binding:
Associate processes with successive cores
if used with one of the -bind-to-* options.
Associate processes with successive processor sockets
if used with one of the -bind-to-* options.
-cpus-per-proc, --cpus-per-proc <#perproc>
Use the number of cores per process
if used with one of the -bind-to-* options.
-cpus-per-rank, --cpus-per-rank <#perrank>
Alias for -cpus-per-proc.
Bind processes to cores.
Bind processes to processor sockets.
Do not bind processes. (Default.)
Report any bindings for launched processes.
-slot-list, --slot-list <slots>
List of processor IDs to be used for binding MPI processes. The specified bindings will
be applied to all MPI processes. See explanation below for syntax.
-rf, --rankfile <rankfile>
Provide a rankfile file.
To manage standard I/O:
-output-filename, --output-filename <filename>
Redirect the stdout, stderr, and stddiag of all ranks to a rank-unique version of
the specified filename. Any directories in the filename will automatically be created.
Each output file will consist of filename.rank, where the rank will be left-filled with
zero's for correct ordering in listings.
-stdin, --stdin <rank>
The MPI rank that is to receive stdin. The default is to forward stdin to rank=0, but this
option can be used to forward stdin to any rank. It is also acceptable to specify none,
indicating that no ranks are to receive stdin.
Tag each line of output to stdout, stderr, and stddiag with [jobid, rank]<stdxxx> indicating the process jobid
and rank that generated the output, and the channel which generated it.
Timestamp each line of output to stdout, stderr, and stddiag.
Provide all output to stdout, stderr, and stddiag in an xml format.
-xterm, --xterm <ranks>
Display the specified ranks in separate xterm windows. The ranks are specified
as a comma-separated list of ranges, with a -1 indicating all. A separate
window will be created for each specified rank.
In some environments, xterm may require that the executable be in the user's
path, or be specified in absolute or relative terms. Thus, it may be necessary
to specify a local executable as "./foo" instead of just "foo". If xterm fails to
find the executable, mpirun will hang, but still respond correctly to a ctrl-c.
If this happens, please check that the executable is being specified correctly
and try again.
To manage files and runtime environment:
-path, --path <path>
<path> that will be used when attempting to locate the requested
executables. This is used prior to using the local PATH setting.
Prefix directory that will be used to set the PATH and
LD_LIBRARY_PATH on the remote node before invoking Open MPI or
the target process. See the "Remote Execution" section, below.
Copy the specified executable(s) to remote machines prior to starting remote processes. The
executables will be copied to the Open MPI session directory and will be deleted upon
completion of the job.
Preload the comma separated list of files to the current working directory of the remote
machines where processes will be launched prior to starting those processes.
The destination directory to be used for preload-files, if other than the current working
directory. By default, the absolute and relative paths provided by --preload-files are used.
Set the root for the session directory tree for mpirun only.
Synonym for -wdir.
Change to the directory <dir> before the user's program executes.
See the "Current Working Directory" section for notes on relative paths.
If the -wdir option appears both on the command line and in an
application context, the context will take precedence over the command
Export the specified environment variables to the remote nodes before
executing the program. Only one environment variable can be specified
per -x option. Existing environment variables can be specified
or new variable names specified with corresponding values. For
% mpirun -x DISPLAY -x OFILE=/tmp/out ...
The parser for the -x option is not very sophisticated; it does
not even understand quoted values. Users are advised to set variables
in the environment, and then use -x to export (not define) them.
Setting MCA parameters:
-gmca, --gmca <key> <value>
Pass global MCA parameters that are applicable to all contexts. <key> is
the parameter name; <value> is the parameter value.
-mca, --mca <key> <value>
Send arguments to various MCA modules. See the "MCA" section, below.
Invoke the user-level debugger indicated by the orte_base_user_debugger
Sequence of debuggers to search for when --debug is used (i.e.
a synonym for orte_base_user_debugger MCA parameter).
Launch processes under the TotalView debugger.
Deprecated backwards compatibility flag. Synonym for --debug.
There are also other options:
-aborted, --aborted <#>
Set the maximum number of aborted processes to display.
Provide an appfile, ignoring all other command line options.
-cf, --cartofile <cartofile>
Provide a cartography file.
Indicates that multiple app_contexts are being provided that are a mix of 32/64-bit binaries.
Do not detach OmpiRTE daemons used by this application. This allows error messages from the daemons
as well as the underlying environment (e.g., when failing to launch a daemon) to be output.
-ompi-server, --ompi-server <uri or file>
Specify the URI of the Open MPI server, or the name of the file (specified as file:filename) that
contains that info. The Open MPI server is used to support multi-application data exchange via
the MPI-2 MPI_Publish_name and MPI_Lookup_name functions.
Pause mpirun before launching the job until ompi-server is detected. This
is useful in scripts where ompi-server may be started in the background, followed immediately by
an mpirun command that wishes to connect to it. Mpirun will pause until either the specified
ompi-server is contacted or the server-wait-time is exceeded.
-server-wait-time, --server-wait-time <secs>
The max amount of time (in seconds) mpirun should wait for the ompi-server to start. The default
is 10 seconds.
The following options are useful for developers; they are not generally
useful to most ORTE and/or MPI users:
Enable debugging of the OmpiRTE (the run-time layer in Open MPI).
This is not generally useful for most users.
Enable debugging of any OmpiRTE daemons used by this application.
Enable debugging of any OmpiRTE daemons used by this application, storing
output in files.
Name of the executable that is to be used to start processes on the remote nodes. The default
is "orted". This option can be used to test new daemon concepts, or to pass options back to the
daemons without having mpirun itself see them. For example, specifying a launch agent of
orted -mca odls_base_verbose 5 allows the developer to ask the orted for debugging output
without clutter from mpirun itself.
Disable the automatic --prefix behavior
There may be other options listed with mpirun --help.
One invocation of mpirun starts an MPI application running under Open
MPI. If the application is single process multiple data (SPMD), the application
can be specified on the mpirun command line.
If the application is multiple instruction multiple data (MIMD), comprising of
multiple programs, the set of programs and argument can be specified in one of
two ways: Extended Command Line Arguments, and Application Context.
An application context describes the MIMD program set including all arguments
in a separate file.
This file essentially contains multiple mpirun command lines, less the
command name itself. The ability to specify different options for different
instantiations of a program is another reason to use an application context.
Extended command line arguments allow for the description of the application
layout on the command line using colons (:) to separate the specification
of programs and arguments. Some options are globally set across all specified
programs (e.g. --hostfile), while others are specific to a single program
Specifying Host Nodes
Host nodes can be identified on the mpirun command line with the -host
option or in a hostfile.
mpirun -H aa,aa,bb ./a.out
launches two processes on node aa and one on bb.
Or, consider the hostfile
% cat myhostfile
Here, we list both the host names (aa, bb, and cc) but also how many "slots"
there are for each. Slots indicate how many processes can potentially execute
on a node. For best performance, the number of slots may be chosen to be the
number of cores on the node or the number of processor sockets. If the hostfile
does not provide slots information, a default of 1 is assumed.
When running under resource managers (e.g., SLURM, Torque, etc.),
Open MPI will obtain both the hostnames and the number of slots directly
from the resource manger.
mpirun -hostfile myhostfile ./a.out
will launch two processes on each of the three nodes.
mpirun -hostfile myhostfile -host aa ./a.out
will launch two processes, both on node aa.
mpirun -hostfile myhostfile -host dd ./a.out
will find no hosts to run on and abort with an error.
That is, the specified host dd is not in the specified hostfile.
Specifying Number of Processes
As we have just seen, the number of processes to run can be set using the
hostfile. Other mechanisms exist.
The number of processes launched can be specified as a multiple of the
number of nodes or processor sockets available. For example,
mpirun -H aa,bb -npersocket 2 ./a.out
launches processes 0-3 on node aa and process 4-7 on node bb,
where aa and bb are both dual-socket nodes.
The -npersocket option also turns on the -bind-to-socket option,
which is discussed in a later section.
mpirun -H aa,bb -npernode 2 ./a.out
launches processes 0-1 on node aa and processes 2-3 on node bb.
mpirun -H aa,bb -npernode 1 ./a.out
launches one process per host node.
mpirun -H aa,bb -pernode ./a.out
is the same as -npernode 1.
Another alternative is to specify the number of processes with the
-np option. Consider now the hostfile
% cat myhostfile
mpirun -hostfile myhostfile -np 6 ./a.out
will launch ranks 0-3 on node aa and ranks 4-5 on node bb. The remaining
slots in the hostfile will not be used since the -np option indicated
that only 6 processes should be launched.
Mapping Processes to Nodes: Using Policies
The examples above illustrate the default mapping of process ranks
to nodes. This mapping can also be controlled with various
mpirun options that describe mapping policies.
Consider the same hostfile as above, again with -np 6:
node aa node bb node cc
mpirun 0 1 2 3 4 5
mpirun -loadbalance 0 1 2 3 4 5
mpirun -bynode 0 3 1 4 2 5
mpirun -nolocal 0 1 2 3 4 5
The -loadbalance option tries to spread processes out fairly among the
The -bynode option does likewise but numbers the processes in "by node"
in a round-robin fashion.
The -nolocal option prevents any processes from being mapped onto the
local host (in this case node aa). While mpirun typically consumes
few system resources, -nolocal can be helpful for launching very
large jobs where mpirun may actually need to use noticeable amounts
of memory and/or processing time.
Just as -np can specify fewer processes than there are slots, it can
also oversubscribe the slots. For example, with the same hostfile:
mpirun -hostfile myhostfile -np 14 ./a.out
will launch processes 0-3 on node aa, 4-7 on bb, and 8-11 on cc. It will
then add the remaining two processes to whichever nodes it chooses.
One can also specify limits to oversubscription. For example, with the same
will produce an error since -nooversubscribe prevents oversubscription.
Limits to oversubscription can also be specified in the hostfile itself:
% cat myhostfile
aa slots=4 max_slots=4
The max_slots field specifies such a limit. When it does, the
slots value defaults to the limit. Now:
mpirun -hostfile myhostfile -np 14 ./a.out
causes the first 12 processes to be launched as before, but the remaining
two processes will be forced onto node cc. The other two nodes are
protected by the hostfile against oversubscription by this job.
Using the --nooversubscribe option can be helpful since Open MPI
currently does not get "max_slots" values from the resource manager.
Of course, -np can also be used with the -H or -host
option. For example,
mpirun -H aa,bb -np 8 ./a.out
launches 8 processes. Since only two hosts are specified, after the first
two processes are mapped, one to aa and one to bb, the remaining processes
oversubscribe the specified hosts.
will launch process 0 running hostname on node aa and processes 1 and 2
each running uptime on nodes bb and cc, respectively.
Mapping Processes to Nodes: Using Arbitrary Mappings
The mapping of process ranks to nodes can be prescribed not just
with general policies but also, if necessary, using arbitrary mappings
that cannot be described by a simple policy. One can use the "sequential
mapper," which reads the hostfile line by line, assigning processes
to nodes in whatever order the hostfile specifies. Use the
-mca rmaps seq option. For example, using the same hostfile
mpirun -hostfile myhostfile ./a.out
will launch three processes, on ranks aa, bb, and cc, respectively.
The slot counts don't matter; one process is launched per line on
whatever node is listed on the line.
Another way to specify arbitrary mappings is with a rank file, which
gives you detailed control over process binding as well. Rank files
are discussed below.
Processes may be bound to specific resources on a node. This can
improve performance if the operating system is placing processes
suboptimally. For example, it might oversubscribe some multi-core
processor sockets, leaving other sockets idle; this can lead
processes to contend unnecessarily for common resources. Or, it
might spread processes out too widely; this can be suboptimal if
application performance is sensitive to interprocess communication
costs. Binding can also keep the operating system from migrating
processes excessively, regardless of how optimally those processes
were placed to begin with.
To bind processes, one must first associate them with the resources
on which they should run. For example, the -bycore option
associates the processes on a node with successive cores. Or,
-bysocket associates the processes with successive processor sockets,
cycling through the sockets in a round-robin fashion if necessary.
And -cpus-per-proc indicates how many cores to bind per process.
But, such association is meaningless unless the processes are actually
bound to those resources. The binding option specifies the granularity
of binding -- say, with -bind-to-core or -bind-to-socket.
One can also turn binding off with -bind-to-none, which is
typically the default.
Finally, -report-bindings can be used to report bindings.
As an example, consider a node with two processor sockets, each comprising
four cores. We run mpirun with -np 4 -report-bindings and
the following additional options:
% mpirun ... -bycore -bind-to-core
[...] ... binding child [...,0] to cpus 0001
[...] ... binding child [...,1] to cpus 0002
[...] ... binding child [...,2] to cpus 0004
[...] ... binding child [...,3] to cpus 0008
% mpirun ... -cpus-per-proc 2 -bind-to-core
[...] ... binding child [...,0] to cpus 0003
[...] ... binding child [...,1] to cpus 000c
[...] ... binding child [...,2] to cpus 0030
[...] ... binding child [...,3] to cpus 00c0
% mpirun ... -bind-to-none
Here, -report-bindings shows the binding of each process as a mask.
In the first case, the processes bind to successive cores as indicated by
the masks 0001, 0002, 0004, and 0008. In the second case, processes bind
to all cores on successive sockets as indicated by the masks 000f and 00f0.
The processes cycle through the processor sockets in a round-robin fashion
as many times as are needed. In the third case, the masks show us that
2 cores have been bind per process. In the fourth case, binding is
turned off and no bindings are reported.
Open MPI's support for process binding depends on the underlying
operating system. Therefore, processing binding may not be available
on every system.
Process binding can also be set with MCA parameters.
Their usage is less convenient than that of mpirun options.
On the other hand, MCA parameters can be set not only on the mpirun
command line, but alternatively in a system or user mca-params.conf file
or as environment variables, as described in the MCA section below.
The correspondences are:
The orte_process_binding value can also take on the
:if-avail attribute. This attribute means that processes
will be bound only if this is supported on the underlying
operating system. Without the attribute, if there is no
such support, the binding request results in an error.
For example, you could have
Rankfiles provide a means for specifying detailed information about
how process ranks should be mapped to nodes and how they should be bound.
Consider the following:
rank 0=aa slot=1:0-2
rank 1=bb slot=0:0,1
rank 2=cc slot=1-2
mpirun -H aa,bb,cc,dd -rf myrankfile ./a.out
Rank 0 runs on node aa, bound to socket 1, cores 0-2.
Rank 1 runs on node bb, bound to socket 0, cores 0 and 1.
Rank 2 runs on node cc, bound to cores 1 and 2.
Application Context or Executable Program?
To distinguish the two different forms, mpirun
looks on the command line for --app option. If
it is specified, then the file named on the command line is
assumed to be an application context. If it is not
specified, then the file is assumed to be an executable program.
If no relative or absolute path is specified for a file, Open
MPI will first look for files by searching the directories specified
by the --path option. If there is no --path option set or
if the file is not found at the --path location, then Open MPI
will search the user's PATH environment variable as defined on the
If a relative directory is specified, it must be relative to the initial
working directory determined by the specific starter used. For example when
using the rsh or ssh starters, the initial directory is $HOME by default. Other
starters may set the initial directory to the current working directory from
the invocation of mpirun.
Current Working Directory
The -wdir mpirun option (and its synonym, -wd) allows
the user to change to an arbitrary directory before the program is
invoked. It can also be used in application context files to specify
working directories on specific nodes and/or for specific
If the -wdir option appears both in a context file and on the
command line, the context file directory will override the command
If the -wdir option is specified, Open MPI will attempt to
change to the specified directory on all of the remote nodes. If this
fails, mpirun will abort.
If the -wdir option is not specified, Open MPI will send
the directory name where mpirun was invoked to each of the
remote nodes. The remote nodes will try to change to that
directory. If they are unable (e.g., if the directory does not exist on
that node), then Open MPI will use the default directory determined by
All directory changing occurs before the user's program is invoked; it
does not wait until MPI_INIT is called.
Open MPI directs UNIX standard input to /dev/null on all processes
except the MPI_COMM_WORLD rank 0 process. The MPI_COMM_WORLD rank 0 process
inherits standard input from mpirun.
The node that invoked mpirun need not be the same as the node where the
MPI_COMM_WORLD rank 0 process resides. Open MPI handles the redirection of
mpirun's standard input to the rank 0 process.
Open MPI directs UNIX standard output and error from remote nodes to the node
that invoked mpirun and prints it on the standard output/error of
Local processes inherit the standard output/error of mpirun and transfer
to it directly.
Thus it is possible to redirect standard I/O for Open MPI applications by
using the typical shell redirection procedure on mpirun.
% mpirun -np 2 my_app < my_input > my_output
Note that in this example only the MPI_COMM_WORLD rank 0 process will
receive the stream from my_input on stdin. The stdin on all the other
nodes will be tied to /dev/null. However, the stdout from all nodes will
be collected into the my_output file.
When orterun receives a SIGTERM and SIGINT, it will attempt to kill
the entire job by sending all processes in the job a SIGTERM, waiting
a small number of seconds, then sending all processes in the job a
SIGUSR1 and SIGUSR2 signals received by orterun are propagated to
all processes in the job.
One can turn on forwarding of SIGSTOP and SIGCONT to the program executed
by mpirun by setting the MCA parameter orte_forward_job_control to 1.
A SIGTSTOP signal to mpirun will then cause a SIGSTOP signal to be sent
to all of the programs started by mpirun and likewise a SIGCONT signal
to mpirun will cause a SIGCONT sent.
Other signals are not currently propagated
Process Termination / Signal Handling
During the run of an MPI application, if any rank dies abnormally
(either exiting before invoking MPI_FINALIZE, or dying as the result of a
signal), mpirun will print out an error message and kill the rest of the
User signal handlers should probably avoid trying to cleanup MPI state
(Open MPI is currently not async-signal-safe; see MPI_Init_thread(3)
for details about
and thread safety). For example, if a segmentation fault occurs in
MPI_SEND (perhaps because a bad buffer was passed in) and a user
signal handler is invoked, if this user handler attempts to invoke
MPI_FINALIZE, Bad Things could happen since Open MPI was already
"in" MPI when the error occurred. Since mpirun will notice that
the process died due to a signal, it is probably not necessary (and
safest) for the user to only clean up non-MPI state.
Processes in the MPI application inherit their environment from the
Open RTE daemon upon the node on which they are running. The
environment is typically inherited from the user's shell. On remote
nodes, the exact environment is determined by the boot MCA module
used. The rsh launch module, for example, uses either
rsh/ssh to launch the Open RTE daemon on remote nodes, and
typically executes one or more of the user's shell-setup files before
launching the Open RTE daemon. When running dynamically linked
applications which require the LD_LIBRARY_PATH environment
variable to be set, care must be taken to ensure that it is correctly
set when booting Open MPI.
See the "Remote Execution" section for more details.
Open MPI requires that the PATH environment variable be set to
find executables on remote nodes (this is typically only necessary in
rsh- or ssh-based environments -- batch/scheduled
environments typically copy the current environment to the execution
of remote jobs, so if the current environment has PATH and/or
LD_LIBRARY_PATH set properly, the remote nodes will also have it
set properly). If Open MPI was compiled with shared library support,
it may also be necessary to have the LD_LIBRARY_PATH environment
variable set on remote nodes as well (especially to find the shared
libraries required to run user MPI applications).
However, it is not always desirable or possible to edit shell
startup files to set PATH and/or LD_LIBRARY_PATH. The
--prefix option is provided for some simple configurations where
this is not possible.
The --prefix option takes a single argument: the base directory
on the remote node where Open MPI is installed. Open MPI will use
this directory to set the remote PATH and LD_LIBRARY_PATH
before executing any Open MPI or user applications. This allows
running Open MPI jobs without having pre-configured the PATH and
LD_LIBRARY_PATH on the remote nodes.
Open MPI adds the basename of the current
node's "bindir" (the directory where Open MPI's executables are
installed) to the prefix and uses that to set the PATH on the
remote node. Similarly, Open MPI adds the basename of the current
node's "libdir" (the directory where Open MPI's libraries are
installed) to the prefix and uses that to set the
LD_LIBRARY_PATH on the remote node. For example:
If the following command line is used:
% mpirun --prefix /remote/node/directory
Open MPI will add "/remote/node/directory/bin" to the PATH
and "/remote/node/directory/lib64" to the D_LIBRARY_PATH on the
remote node before attempting to execute anything.
Note that --prefix can be set on a per-context basis, allowing
for different values for different nodes.
The --prefix option is not sufficient if the installation paths
on the remote node are different than the local node (e.g., if "/lib"
is used on the local node, but "/lib64" is used on the remote node),
or if the installation paths are something other than a subdirectory
under a common prefix.
Note that executing mpirun via an absolute pathname is
equivalent to specifying --prefix without the last subdirectory
in the absolute pathname to mpirun. For example:
% /usr/local/bin/mpirun ...
is equivalent to
% mpirun --prefix /usr/local
Exported Environment Variables
All environment variables that are named in the form OMPI_* will automatically
be exported to new processes on the local and remote nodes.
The -x option to mpirun can be used to export specific environment
variables to the new processes. While the syntax of the -x
option allows the definition of new variables, note that the parser
for this option is currently not very sophisticated - it does not even
understand quoted values. Users are advised to set variables in the
environment and use -x to export them; not to define them.
Setting MCA Parameters
The -mca switch allows the passing of parameters to various MCA
(Modular Component Architecture) modules.
MCA modules have direct impact on MPI programs because they allow tunable
parameters to be set at run time (such as which BTL communication device driver
to use, what parameters to pass to that BTL, etc.).
The -mca switch takes two arguments: <key> and <value>.
The <key> argument generally specifies which MCA module will receive the value.
For example, the <key> "btl" is used to select which BTL to be used for
transporting MPI messages. The <value> argument is the value that is
mpirun -mca btl tcp,self -np 1 foo
Tells Open MPI to use the "tcp" and "self" BTLs, and to run a single copy of
"foo" an allocated node.
mpirun -mca btl self -np 1 foo
Tells Open MPI to use the "self" BTL, and to run a single copy of "foo" an
The -mca switch can be used multiple times to specify different
<key> and/or <value> arguments. If the same <key> is
specified more than once, the <value>s are concatenated with a comma
(",") separating them.
Note that the -mca switch is simply a shortcut for setting environment variables.
The same effect may be accomplished by setting corresponding environment
variables before running mpirun.
The form of the environment variables that Open MPI sets is:
Thus, the -mca switch overrides any previously set environment
variables. The -mca settings similarly override MCA parameters set
$OPAL_PREFIX/etc/openmpi-mca-params.conf or $HOME/.openmpi/mca-params.conf
Unknown <key> arguments are still set as
environment variable -- they are not checked (by mpirun) for correctness.
Illegal or incorrect <value> arguments may or may not be reported -- it
depends on the specific MCA module.
To find the available component types under the MCA architecture, or to find the
available parameters for a specific component, use the ompi_info command.
See the ompi_info(1) man page for detailed information on the command.
Be sure also to see the examples throughout the sections above.
mpirun -np 4 -mca btl ib,tcp,self prog1
Run 4 copies of prog1 using the "ib", "tcp", and "self" BTL's for the
transport of MPI messages.
mpirun -np 4 -mca btl tcp,sm,self
--mca btl_tcp_if_include eth0 prog1
Run 4 copies of prog1 using the "tcp", "sm" and "self" BTLs for the
transport of MPI messages, with TCP using only the eth0 interface to
communicate. Note that other BTLs have similar if_include MCA
mpirun returns 0 if all ranks started by mpirun exit after calling
MPI_FINALIZE. A non-zero value is returned if an internal error occurred in
mpirun, or one or more ranks exited before calling MPI_FINALIZE. If an
internal error occurred in mpirun, the corresponding error code is returned.
In the event that one or more ranks exit before calling MPI_FINALIZE, the
return value of the rank of the process that mpirun first notices died
before calling MPI_FINALIZE will be returned. Note that, in general, this will
be the first rank that died but is not guaranteed to be so.