The format of the mpirun command is as follows:

mpirun [global_options ]entry[: entry ... ]

The global_options operand applies to all MPI executable files on all specified hosts. The following global options are supported:

mpirun -cpr -np 2 ./a.out >&1/dev/null 

mpirun -cpr 2 ./a.out : 3 ./b.out
mpirun -cpr hosta -np 2 ./a.out>out 2>&1  mpirun -cpr hosta -np 2 ./a.out>out 2>&1  </dev/null

main(int argc, char **argv)
{
   MPI_Init(&argc, &argv);

   printf("Hello world\n");

   MPI_Finalize();
}

mpirun -np 2 a.out
Hello world
Hello world

mpirun -prefix ">" -np 2 a.out
>Hello world
>Hello world

mpirun -prefix "%g" 2 a.out
0Hello world
1Hello world

mpirun -prefix "[%g] " 2 a.out
[0] Hello world
[1] Hello world

mpirun -prefix "<process %g out of %G> " 4 a.out

<process 1 out of 4> Hello world
<process 0 out of 4> Hello world
<process 3 out of 4> Hello world
<process 2 out of 4> Hello world

mpirun -prefix "%@: " hosta,hostb 1 a.out

hosta: Hello world
hostb: Hello world

mpirun -prefix "%@ (%l out of %L) %g: " hosta 2, hostb 3 a.out

hosta (0 out of 2) 0: Hello world
hosta (1 out of 2) 1: Hello world
hostb (0 out of 3) 2: Hello world
hostb (1 out of 3) 3: Hello world
hostb (2 out of 3) 4: Hello world

mpirun -prefix "%@ (%h out of %H): " hosta,hostb,hostc 2 a.out

hosta (0 out of 3): Hello world
hostb (1 out of 3): Hello world
hostc (2 out of 3): Hello world
hosta (0 out of 3): Hello world
hostc (2 out of 3): Hello world
hostb (1 out of 3): Hello world

The entry operand describes a host on which to run a program, and the local options for that host. You can list any number of entries on the mpirun command line.

In the common case (same program, multiple data (SPMD)), in which the same program runs with identical arguments on each host, usually, you need to specify only one entry.

Each entry has the following components:

An entry has the following format:

host_list local_options program program_arguments

The host_list operand is either a single host (machine name) or a comma-separated list of hosts on which to run an MPI program.

The local_options operand contains information that applies to a specific host list. The following local options are supported:

The program program_arguments operand specifies the name of the program that you are running and its accompanying options.

Because the full specification of a complex job can be lengthy, you can enter mpirun arguments in a file and use the -f option to specify the file on the mpirun command line, as in the following example:

mpirun -f my_arguments

The arguments file is a text file that contains argument segments. White space is ignored in the arguments file, so you can include spaces and newline characters for readability. An arguments file can also contain additional -f options.

For testing and debugging, it is often useful to run an MPI program only on the local host without distributing it to other systems. To run the application locally, enter mpirun with the -np argument. Your entry must include the number of processes to run and the name of the MPI executable file.

The following command starts three instances of the application mtest, to which is passed an arguments list (arguments are optional).

mpirun -np 3 mtest 1000 "arg2"

You are not required to use a different host in each entry that you specify on the mpirun(1) command. You can launch a job that has two executable files on the same host. In the following example, both executable files use shared memory:

mpirun host_a -np 6 a.out : host_a -np 4 b.out

You can use mpirun(1) to launch a program that consists of any number of executable files and processes and distribute it to any number of hosts. A host is usually a single machine, or, for IRIX systems, can be any accessible computer running Array Services software. For available nodes on systems running Array Services software, see the /usr/lib/array/arrayd.conf file. Array Services is not supported on Linux systems currently, so an alternate launching mechanism is used.

You can list multiple entries on the mpirun command line. Each entry contains an MPI executable file and a combination of hosts and process counts for running it. This gives you the ability to start different executable files on the same or different hosts as part of the same MPI application.

The following examples show various ways to launch an application that consists of multiple MPI executable files on multiple hosts.

The following example runs ten instances of the a.out file on host_a:

mpirun host_a -np 10 a.out

When specifying multiple hosts, you can omit the -np or -nt option, listing the number of processes directly. The following example launches ten instances of fred on three hosts. fred has two input arguments.

mpirun host_a, host_b, host_c 10 fred arg1 arg2

The following example launches an MPI application on different hosts with different numbers of processes and executable files, using an array called test:

mpirun -array test host_a 6 a.out : host_b 26 b.out

The following example launches an MPI application on different hosts out of the same directory on both hosts:

mpirun -d /tmp/mydir host_a 6 a.out : host_b 26 b.out

To use the MPI-2 process creation functions MPI_Comm_spawn or MPI_Comm_spawn_multiple, the user must specify the universe size by specifying the -up option on the mpirun command line.

For example, the following command starts three instances of the MPI application mtest in a universe of size 10:

mpirun -up 10 -np 3 mtest

Up to 7 more MPI processes can be started by mtest via one of the spawn commands.

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Note: This implementation does not support spawn capable mode for MPI jobs launched via certain batch schedulers, nor does it support a spawn capability for MPI jobs spanning multiple hosts.

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