10.11. Unusual jobs
Open MPI can run many types of applications, including non-MPI programs. This section describes some of the less common kinds of programs that can be executed.
Non-MPI programs can be launched with mpirun(1), for example:
shell$ mpirun -n 2 --host a,b uptime
This will launch a copy of the Unix command
uptime on the hosts
mpirun(1) works equally well for MPI and non-MPI applications.
10.11.2. Running GUI applications
Running GUI applications depends on your local setup and may require additional setup.
You will need to have graphics forwarding (e.g., X11
forwarding) enabled from the remote processes to the display where you
want output to appear. In a secure environment, you can simply allow
all X requests to be shown on the target display and set the
DISPLAY environment variable in all MPI processes’ environments to
the target display, perhaps something like this:
shell$ hostname my_desktop.secure-cluster.example.com shell$ xhost + shell$ mpirun -n 4 -x DISPLAY=my_desktop.secure-cluster.example.com a.out
However, this technique is not generally suitable for unsecure environments (because it allows anyone to read and write to your display). A slightly more secure way is to only allow X connections from the nodes where your application will be running:
shell$ hostname my_desktop.secure-cluster.example.com shell$ xhost +compute1 +compute2 +compute3 +compute4 compute1 being added to access control list compute2 being added to access control list compute3 being added to access control list compute4 being added to access control list shell$ mpirun -n 4 -x DISPLAY=my_desktop.secure-cluster.example.com a.out
(assuming that the four nodes you are running on are
Other methods are available, but they involve sophisticated X forwarding through mpirun(1) and are generally more complicated than desirable.
10.11.3. Running curses-based applications
Open MPI provides fairly sophisticated stdin / stdout / stderr forwarding. However, it does not work well with curses, ncurses, readline, or other sophisticated I/O packages that generally require direct control of the terminal.
Every application and I/O library is different — you should try to see if yours is supported. But chances are that it won’t work.
10.11.4. Launching an MPMD MPI job
Open MPI supports multiple program, multiple data (MPMD) style launches, either from the command line or from a file. For example:
shell$ mpirun -n 2 a.out : -n 2 b.out
This will launch a single parallel application, but the first two
processes will be instances of the
a.out executable, and the
second two processes will be instances of the
In MPI terms, this will be a single
MPI_COMM_WORLD, but the
a.out processes will be ranks 0 and 1 in
b.out processes will be ranks 2 and 3 in
mpirun(1) can also accept a parallel application specified in a file instead of on the command line. For example:
shell$ mpirun --app my_appfile
where the file
my_appfile contains the following:
# Comments are supported; comments begin with # # Application context files specify each sub-application in the # parallel job, one per line. The first sub-application is the 2 # a.out processes: -n 2 a.out # The second sub-application is the 2 b.out processes: -n 2 b.out
This will result in the same behavior as running
from the command line.
10.11.5. Connecting independent MPI applications
In certain environments, Open MPI supports connecting multiple,
independent MPI applications using mechanism defined in the MPI
specification such as
MPI_Comm_connect() / MPI_Comm_accept() and
publishing connection information using
MPI_Lookup_name(). These mechanisms require a centralized service
to exchange contact information across multiple jobs.
Beginning with Open MPI v5.0.0 this can be achieved by starting an
instance of the prte server with the
report-uri option to
display the contact information of the prte server. This information
can then be used for launching subsequent MPI applications.
The following commands show an example for launching two MPI jobs that will connect to each other at runtime using the MPI-2 based functionality.
Step 1: start the standalone prte server
user@myhost:~/ompi-install/bin$ ./prte --report-uri <filename> DVM ready
Step 2: Launch the first MPI application providing the uri of the prte server
user@myhost:~/app1-dir$ mpiexec --dvm file:<filename> -np 4 ./mpi_app_1
Step 3: Launch the second MPI application providing the uri of the prte server again
user@myhost:~/app2-dir$ mpiexec --dvm file:<filename> -np 4 ./mpi_app_2
In case the prte server has been started as a system server using the
--system-server argument (e.g. the nodes used by the MPI
applications are not shared by multiple jobs), the sequence can be
simplified by using
mpiexec --dvm system or
system-first instead of the uri of the prte server.