mpirun command

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Note: mpirun, mpiexec, and orterun are all synonyms. Using any of the names will produce the same behavior. http://www.open-mpi.org/doc/v1.4/man1/mpiexec.1.php

About the mpirun Command
Syntax for the mpirun Command
mpirun Command Examples
Mapping MPI Processes to Nodes
Controlling Input/Output
Controlling Other Job Attributes
Submitting Jobs Under Sun Grid Engine Integration
Using MPI Client/Server Applications
mpirun Command Reference
For More Information

Note - The mpirun, mpiexec, and orterun commands all perform the same function, and they can be used interchangeably.

The mpirun command controls several aspects of program execution in Open MPI. mpirun uses the Open Run-Time Environment (ORTE) to launch jobs. If you are running under distributed resource manager software, such as Sun Grid Engine or PBS, ORTE launches the resource manager for you.

If you are using rsh/ssh instead of a resource manager, you must use a hostfile or host list to identify the hosts on which the program will be run. When you issue the mpirun command, you specify the name of the hostfile or host list on the command line; otherwise, mpirun executes all the copies of the program on the local host, in round-robin sequence by CPU slot. For more information about hostfiles and their syntax, see Specifying Hosts By Using a Hostfile.

Both MPI programs and non-MPI programs can use mpirun to launch the user processes.

Some example programs are provided in the /opt/SUNWhpc/HPC8.1/examples directory for you to try to compile/run as sanity tests.

Syntax for the mpirun Command

The following example shows the general single-process syntax for mpirun:

% mpirun [options] [program-name]

For a simple SPMD (Single Process, Multiple Data) job, the typical syntax is:

% mpirun -np x program-name

For jobs involving multiple instructions, the command syntax appears similar to the following:

% mpirun [options] [program-name] : [options2] [program-name2] ...

For an MPMD (Multiple Program, Multiple Data) parallel application, the syntax follows this form:

% mpirun -np x program1 : -np y program2

This command starts x number of copies of the program program1, and then starts y copies of the program program2.

mpirun Options

The options control the behavior of the mpirun command. They might or might not be followed by arguments.

Caution - If you do not specify an argument for an option that expects to be followed by an argument (for example, the --app<filename> option), that option will read the next option on the command line as an argument. This might result in inconsistent behavior.

“Invalid Cross-Reference Format” lists the options in alphabetical order, with a brief description of each.

Using Environment Variables With the mpirun Command

Use the -x args option (where args is the environment variable(s) you want to use) to specify any environment variable you want to pass during runtime. The -x option exports the variable specified in args and sets the value for args from the current environment. For example:

% mpirun -x LD_LIBRARY_PATH=/opt/SUNWhpc/HPC8.1/lib -np 4 a.out

Using MCA Parameters With the mpirun Command

The mpirun command uses MCA (Multiple Component Architecture) parameters to pass environment variables. To specify an MCA parameter, use the -mca option with the mpirun command, and then specify the parameter type, the parameter you want to pass as an environment variable, and the value you want to set. For example:

% mpirun --mca mpi_show_handle_leaks 1 -np 4 a.out

This sets the MCA parameter mpi_show_handle_leaks to the value of 1 before running the program named a.out with four processes. In general, the format used on the command line is --mca parameter_name value.

Note - There are multiple ways to specify the values of MCA parameters. This chapter discusses how to use them from the command line with the mpirun command. MCA parameters are discussed in more detail in Chapter 7.

Canceling Send and Receive Operations

Open MPI supports the canceling of receive operations. However, the canceling of sends is not supported; therefore, a send will never be successfully canceled.

For more information about canceling send and receive operations, see the MPI_Cancel(3) man page.

mpirun Command Examples

The examples in this section show how to use the mpirun command options to specify how and where the processes and programs run.

The following table shows the process control options for the mpirun command. The procedures that follow the table explain how these options are used and show the syntax for each.

TABLE 5-1 Program/Process Control Options
Task	mpirun option
To run a program with default settings	(no need to specify an option)
To run multiple parallel processes	`-c` or`-np` <number of processes>
To display command help	`-h` or `--help`
To change the working directory	`-wdir` or `--wdir` <directory>
To specify the list of hosts on which to invoke processes (also known as the rankmap string)	`-host` or `--host` or `-H`
To specify the list of hosts on which to execute the program (also known as the rankmap file)	`-hostfile` <filename> or `--hostfile` <filename> or `-machinefile` <filename> or `--machinefile` <filename>
To start up in debugging mode	-d or --debug or -debugger or --debugger <sequence>
To specify verbose output	`-v`
To specify multiple executables	`-np 2 exe1 : -np 6 exe2`

To Run a Program With Default Settings

To run the program with default settings, enter the command and program name, followed by any required arguments to the program:

% mpirun program-name

To Run Multiple Processes

By default, an MPI program started with mpirun runs as one process.

To run the program as multiple processes, use the -np option:

% mpirun -np process-count program-name

When you request multiple processes, ORTE attempts to start the number of processes you request, regardless of the number of CPUs available to run those processes. For more information, see Oversubscribing Nodes.

To Direct `mpirun` By Using an Appfile

You can use a type of text file (called an appfile) to direct mpirun. The appfile specifies the nodes on which to run, the number of processes to launch on each node, and the programs to execute in a parallel application. When you use the
--app option, mpirun takes all its direction from the contents of the appfile and ignores any other nodes or processes specified on the command line.

For example the following shows an appfile called my_appfile:

# 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:
-np 2 a.out
# The second sub-application is the 2 b.out processes:
-np 2 b.out

To use the --app option with the mpirun command, specify the name and path of the appfile on the command line. For example:

% mpirun --app my_appfile

This command produces the same results as running a.out and b.out from the command line.

Mapping MPI Processes to Nodes

When you issue the mpirun command from the command line, ORTE reads the number of processes to be launched from the -np option, and then determines where the processes will run.

To determine where the processes will run, ORTE uses the following criteria:

Available hosts (also referred to as nodes), specified by a hostfile or by the
--host option
Scheduling policy (round-robin or by-slot)
Default and maximum numbers of slots available on each host
ORTE also checks to see whether the current environment/shell runs with any third-party launcher (such as Sun Grid Engine or PBS) to determine where the processes will launch.

Specifying Available Hosts

You specify the available hosts to Open MPI in three ways:

Through the batch scheduler in your resource management software. This option is described in detail in Chapter 6.
By using a hostfile with the --hostfile option. The hostfile is a text file that contains the names of hosts, the number of available slots on each host, and the maximum slots on each host.
By using the --host option. Use this option to specify which hosts to include or exclude.

Specifying Hosts By Using a Hostfile

The hostfile lists each node, the available number of slots, and the maximum number of slots on that node. For example, the following listing shows a simple hostfile:

node0 
node1 slots=2 
node2 slots=4 max_slots=4
node3 slots=4 max_slots=20

In this example file, node0 is a single-processor machine. node1 has two slots. node2 and node3 both have 4 slots, but the values of slots and max_slots are the same (4) on node2. This disallows the processors on node2 from being oversubscribed. The four slots on node3 can be oversubscribed, up to a maximum of 20 processes.

When you use this hostfile with the --nooversubscribe option (see Oversubscribing Nodes), mpirun assumes that the value of max_slots for each node in the hostfile is the same as the value of slots for each node. It overrides the values for max_slots set in the hostfile.

Open MPI assumes that the maximum number of slots you can specify is equal to infinity, unless explicitly specified. Resource managers also do not specify the maximum number of available slots.

Note - Open MPI includes a commented default hostfile at /opt/SUNWhpc/HPC8.1/etc/openmpi-default-hostfile. Unless you specify a different hostfile at a different location, this is the hostfile that OpenMPI uses. It is empty by default, but you may edit this file to add your list of nodes. See the comments in the hostfile for more information.

Specifying Hosts By Using the `--host` Option

You can use the --host option to mpirun to specify the hosts you want to use on the command line in a comma-delimited list. For example, the following command directs mpirun to run a program called a.out on hosts a, b, and c:

% mpirun -np 3 --host a,b,c a.out

Open MPI assumes that the default number of slots on each host is one, unless you explicitly specify otherwise.

To Specify Multiple Slots Using the --host Option

To specify multiple slots with the -host option for each host repeat the host name on the command line for each slot you want to use. For example:

% mpirun -host node1,node1,node2,node2 ...

If you are using a resource manager such as Sun Grid Engine or PBS, the resource manager maintains an accurate count of available slots.

Excluding Hosts From Scheduling By Using the `--host` Option

You can also use the --host option in conjunction with a hostfile to exclude any nodes not explicitly specified on the command line. For example, assume that you have the following hostfile call /tr>

Suppose you issue the following command to run program a.out:

% mpirun -np 1 --hostfile my_hosts --host c a.out

This command launches one instance of a.out on host c, but excludes the other hosts in the hostfile (a, b, and d).

Note - If you use these two options (--hostfile and --host) together, make sure that the host(s) you specify using the --host option also exist in the hostfile. Otherwise, mpirun exits with an error.

Oversubscribing Nodes

If you schedule more processes to run than there are available slots, this is referred to as oversubscribing. Oversubscribing a host is not suggested, as it might result in performance degradation.

mpirun has a --nooversubscribe option. This option implicitly sets the max_slots value (maximum number of available slots) to the same value as the slots value for each node, as specified in your hostfile. If the number of processes requested is greater than the slots value, mpirun returns an error and does not execute the command. This option overrides the value set for max_slots in your hostfile.

For more information about oversubscribing, see the following URL:

http://www.open-mpi.org/faq/?category=running#oversubscribing

Scheduling Policies

ORTE uses two types of scheduling policies when it determines where processes will run:

By slot (default). This scheme schedules processes to run on each successive slot on one host. When all those slots are filled, scheduling begins on the next host in the hostfile.
By node. In this scheme, Open MPI schedules the processes by finding the first available slot on a host, then the first available slot on the next host in the hostfile, and so on, in a round-robin fashion.

Scheduling By Slot

This is the default scheduling policy for Open MPI. If you do not specify a scheduling policy, this is the policy that is used.

In by-slot scheduling, Open MPI schedules processes on a node until all of its available slots are exhausted (that is, all slots are running processes) before proceeding to the next node. In MPI terms, this means that Open MPI tries to maximize the number of adjacent ranks in MPI_COMM_WORLD on the same host without oversubscribing that host.

To Specify By-Slot Scheduling

If you want to explicitly specify by-slot scheduling for some reason, there are two ways to do it:

1. Specify the --byslot option to mpirun. For example, the following command specifies the --byslot and --hostfile options:

% mpirun -np 4 --byslot --hostfile myfile a.out

The following example uses the -host option:

% mpirun -np 4 --byslot -host node0,node0,node1,node1 a.out

2. Set the MCA parameter rmaps_base_schedule_policy to the value slot. For example:

% mpirun --mca rmaps_base_schedule_policy slot -np 4 a.out

Note - The examples in this chapter set MCA parameters on the command line. For more information about the ways in which you can set MCA parameters, see Chapter 7. In addition, the Open MPI FAQ contains information about MCA parameters at the following URL:

http://www.open-mpi.org/faq/?category=tuning#setting-mca-params

The following output example shows the contents of a simple hostfile called my-hosts and the results of the mpirun command using by-slot scheduling.

% cat my-hosts
node0 slots=2 max_slots=20
node1 slots=2 max_slots=20
% mpirun --hostfile my-hosts -np 8 --byslot hello | sort
Hello World I am rank 0 of 8 running on node0
Hello World I am rank 1 of 8 running on node0
Hello World I am rank 2 of 8 running on node1
Hello World I am rank 3 of 8 running on node1
Hello World I am rank 4 of 8 running on node0
Hello World I am rank 5 of 8 running on node0
Hello World I am rank 6 of 8 running on node1
Hello World I am rank 7 of 8 running on node1

Scheduling By Node

In by-node scheduling, Open MPI schedules a single process on each node in a round-robin fashion (looping back to the beginning of the node list as necessary) until all processes have been scheduled. Nodes are skipped once their default slot counts are exhausted.

To Specify By-Node Scheduling

There are two ways to specify by-node scheduling:

Specify the --bynode option to mpirun. For example:

% mpirun -np 4 --bynode --hostfile my-hosts a.out

Set the MCA parameter rmaps_base_schedule_policy to the value node. For example:
```
% mpirun --mca rmaps_base_schedule_policy node -np 4 a.out
```

The following output example shows the contents of the same hostfile used in the previous example and the results of the mpirun command using by-node scheduling.

% cat my-hosts
node0 slots=2 max_slots=20
node1 slots=2 max_slots=20
% mpirun --hostfile my-hosts -np 8 --bynode hello | sort
Hello World I am rank 0 of 8 running on node0
Hello World I am rank 1 of 8 running on node1
Hello World I am rank 2 of 8 running on node0
Hello World I am rank 3 of 8 running on node1
Hello World I am rank 4 of 8 running on node0
Hello World I am rank 5 of 8 running on node1
Hello World I am rank 6 of 8 running on node0
Hello World I am rank 7 of 8 running on node1

Comparing By-Slot to By-Node Scheduling

In the examples in this section, node0 and node1 each have two slots. The diagrams show the differences in scheduling between the two methods.

By-slot scheduling for the two nodes can be represented as follows:

node0

node1

0

2

1

3

4

6

5

7

By-node scheduling for the same two nodes can be represented this way:

node0

node1

0

1

2

3

4

5

6

7

Controlling Input/Output

Open MPI directs UNIX standard input to /dev/null on all processes except the rank 0 process of MPI_COMM_WORLD. The MPI_COMM_WORLD rank 0 process inherits standard input from mpirun. The node from which you invoke mpirun need not be the same as the node where the MPI_COMM_WORLD rank 0 process resides. Open MPI handles the redirection of the mpirun standard input to the rank 0 process.

Open MPI directs UNIX standard output and standard error from remote nodes to the node that invoked mpirun, and then prints the information from the remote nodes on the standard output/error of mpirun. Local processes inherit the standard output/error of mpirun and transfer to it directly.

To Redirect Standard I/O

To redirect standard I/O for Open MPI applications, use the typical shell redirection procedure on mpirun. For example:

% mpirun -np 2 my_app < my_input > my_output

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.

Controlling Other Job Attributes

To Perform This Task	Use This Option
To change the working directory	-wdir or --wdir
To display debugging output	-d
To display command help	-h

To Change the Working Directory

Use the -wdir or --wdir option to specify the path of an alternative working directory to be used by the processes spawned when you run your program:

% mpirun --wdir working-directory program-name

Setting a path with --wdir does not affect where the runtime environment looks for executables. If you do not specify --wdir, the default is the current working directory. For example:

% mpirun --wdir /home/mystuff/bin a.out

The syntax above changes the working directory for a.out to /home/mystuff/bin.

To Specify Debugging Output

Use this syntax to specify debugging output. For example:

% mpirun -d a.out

The -d option shows the user-level debugging output for all of the ORTE modules used with mpirun. To see more information from a particular module, you can set additional MCA debugging parameters. The availability of the additional debugging information depends on how the module of interest is implemented.

For more information on MCA parameters, see Chapter 7. For more information about whether a module provides additional verbose or debug mode, run the ompi_info command on that module.

To Display Command Help (`-h`)

To display a list of mpirun options, use the -h option (alone). The following example shows the output from mpirun -h:

% ./mpirun -h
mpirun (Open MPI) 1.3r19845-ct8.1-b06a-r21
 
Usage: mpirun [OPTION]...  [PROGRAM]...
Start the given program using Open RTE
 
   -am <arg0>            Aggregate MCA parameter set file list
   --app <arg0>          Provide an appfile; ignore all other command line
                         options
   -bynode|--bynode      Whether to allocate/map processes round-robin by
                         node
   -byslot|--byslot      Whether to allocate/map processes round-robin by
                         slot (the default)
-c|-np|--np <arg0>       Number of processes to run
   -cf|--cartofile <arg0>
                         Provide a cartography file
-d|-debug-devel|--debug-devel
                         Enable debugging of OpenRTE
   -debug|--debug        Invoke the user-level debugger indicated by the
                         orte_base_user_debugger MCA parameter
   -debug-daemons|--debug-daemons
                         Enable debugging of any OpenRTE daemons used by
                         this application
   -debug-daemons-file|--debug-daemons-file
                         Enable debugging of any OpenRTE daemons used by
                         this application, storing output in files
   -debugger|--debugger <arg0>
                         Sequence of debuggers to search for when "--debug"
                         is used
   -default-hostfile|--default-hostfile <arg0>
                         Provide a default hostfile
   -display-allocation|--display-allocation
                         Display the allocation being used by this job
   -display-devel-allocation|--display-devel-allocation
                         Display a detailed list (mostly intended for
                         developers) of the allocation being used by this
                         job
   -display-devel-map|--display-devel-map
                         Display a detailed process map (mostly intended for
                         developers) just before launch
   -display-map|--display-map
                         Display the process map just before launch
   -do-not-launch|--do-not-launch
                         Perform all necessary operations to prepare to
                         launch the application, but do not actually launch
                         it
   -do-not-resolve|--do-not-resolve
                         Do not attempt to resolve interfaces
   -gmca|--gmca <arg0> <arg1>
                         Pass global MCA parameters that are applicable to
                         all contexts (arg0 is the parameter name; arg1 is
                         the parameter value)
-h|--help                This help message
-H|-host|--host <arg0>   List of hosts to invoke processes on
   --hetero              Indicates that multiple app_contexts are being
                         provided that are a mix of 32/64 bit binaries
   -hostfile|--hostfile <arg0>
                         Provide a hostfile
   -launch-agent|--launch-agent <arg0>
                         Command used to start processes on remote nodes
                         (default: orted)
   -leave-session-attached|--leave-session-attached
                         Enable debugging of OpenRTE
   -loadbalance|--loadbalance
                         Balance total number of procs across all allocated
                         nodes
   -machinefile|--machinefile <arg0>
                         Provide a hostfile
   -mca|--mca <arg0> <arg1>
                         Pass context-specific MCA parameters; they are
                         considered global if --gmca is not used and only
                         one context is specified (arg0 is the parameter
                         name; arg1 is the parameter value)
   -n|--n <arg0>         Number of processes to run
   -nolocal|--nolocal    Do not run any MPI applications on the local node
   -nooversubscribe|--nooversubscribe
                         Nodes are not to be oversubscribed, even if the
                         system supports such operation
   --noprefix            Disable automatic --prefix behavior
   -npernode|--npernode <arg0>
                         Launch n processes per node on all allocated nodes
   -ompi-server|--ompi-server <arg0>
                         Specify the URI of the Open MPI server, or the name
                         of the file (specified as file:filename) that
                         contains that info
   -path|--path <arg0>   PATH to be used to look for executables to start
                         processes
   -pernode|--pernode    Launch one process per available node on the
                         specified number of nodes [no -np => use all
                         allocated nodes]
   --prefix <arg0>       Prefix where Open MPI is installed on remote nodes
   --preload-files <arg0>
                         Preload the comma separated list of files to the
                         remote machines current working directory before
                         starting the remote process.
   --preload-files-dest-dir <arg0>
                         The destination directory to use in conjunction
                         with --preload-files. By default the absolute and
                         relative paths provided by --preload-files are
                         used.
-q|--quiet               Suppress helpful messages
   -rf|--rankfile <arg0>
                         Provide a rankfile file
-s|--preload-binary      Preload the binary on the remote machine before
                         starting the remote process.
   -server-wait-time|--server-wait-time <arg0>
                         Time in seconds to wait for ompi-server (default:
                         10 sec)
   -slot-list|--slot-list <arg0>
                         List of processor IDs to bind MPI processes to
                         (e.g., used in conjunction with rank files)
   -tmpdir|--tmpdir <arg0>
                         Set the root for the session directory tree for
                         orterun ONLY
   -tv|--tv              Deprecated backwards compatibility flag; synonym
                         for "--debug"
-v|--verbose             Be verbose
-V|--version             Print version and exit
   -wait-for-server|--wait-for-server
                         If ompi-server is not already running, wait until
                         it is detected (default: false)
   -wd|--wd <arg0>       Synonym for --wdir
   -wdir|--wdir <arg0>   Set the working directory of the started processes
-x <arg0>                Export an environment variable, optionally
                         specifying a value (e.g., "-x foo" exports the
                         environment variable foo and takes its value from
                         the current environment; "-x foo=bar" exports the
                         environment variable name foo and sets its value to
                         "bar" in the started processes)
   -xml|--xml            Provide all output in XML format
 
Report bugs to http://www.open-mpi.org/community/help/

Submitting Jobs Under Sun Grid Engine Integration

There are two ways to submit jobs under Sun Grid Engine integration: interactive mode and batch mode. The instructions in this chapter describe how to submit jobs interactively. For information about how to submit jobs in batch mode, see Chapter 6.

Defining Parallel Environment (PE) and Queue

A PE needs to be defined for all the queues in the Sun Grid Engine cluster to be used as ORTE nodes. Each ORTE node should be installed as an Sun Grid Engine execution host. To allow the ORTE to submit a job from any ORTE node, configure each ORTE node as a submit host in Sun Grid Engine.

Each execution host must be configured with a default queue. In addition, the default queue set must have the same number of slots as the number of processors on the hosts.

To Use PE Commands

To display a list of available PEs (parallel environments), type the following:

% qconf -spl
make

To define a new PE, you must have Sun Grid Engine manager or operator privileges. Use a text editor to modify a template for the PE. The following example creates a PE named orte.

% qconf -ap orte

To modify an existing PE, use this command to invoke the default editor:

% qconf -mp orte

To show a particular PE that has been defined, type this command:

% qconf -sp orte
pe_name           orte
slots             8
user_lists        NONE
xuser_lists       NONE
start_proc_args   /bin/true
stop_proc_args    /bin/true
allocation_rule   $round_robin
control_slaves    TRUE
job_is_first_task FALSE
urgency_slots     min

The value NONE in user_lists and xuser_lists mean enable everybody and exclude nobody.

The value of control_slaves must be TRUE; otherwise, qrsh exits with an error message.

The value of job_is_first_task must be FALSE or the job launcher consumes a slot. In other words, mpirun itself will count as one of the slots and the job will fail, because only n-1 processes will start.

To Use Queue Commands

To show all the defined queues, type the following command:

% qconf -sql
all.q

The queue all.q is set up by default in Sun Grid Engine.

To configure the orte PE from the example in the previous section to the existing queue, type the following:

% qconf -mattr queue pe_list "orte" all.q

You must have Sun Grid Engine manager or operator privileges to use this command.

Submitting Jobs in Interactive Mode

To Set the Interactive Display

Before you submit a job, you must have your DISPLAY environment variable set so that the interactive window will appear on your desktop, if you have not already done so.

For example, if you are working in the C shell, type the following command:

setenv DISPLAY desktop:0.0

To Submit Jobs Interactively

1. Use the source command to set the Sun Grid Engine environment variables from a file:

mynode4% source /opt/sge/default/common/settings.csh

2. Use the qsh command to start the interactive X Windows session, and specify the parallel environment (in this example, ORTE) and the number of slots to use:

mynode4% qsh -pe orte 2 
waiting for interactive job to be scheduled... 
Your interactive job 324 has been successfully scheduled.

3. On a different node in the cluster, use the cd command to switch to the directory where your executable is located.

mynode5% cd /workspace/joeuser/ompi/trunk/builds/sparc32-g/bin

4. Issue the mpirun command.

mynode5% /opt/SUNWhpc/HPC8.1/sun/bin/mpirun -np 4 hostname

In the above example, Sun Grid Engine starts the user executable hostname with 4 processes on the two Sun Grid Engine assigned slots. The following example shows the output from the mpirun command with the specified options.

mynode5% /opt/SUNWhpc/HPC8.1/sun/bin/mpirun -np 4 --hostname mynode5
 
mynode5

To Verify That Sun Grid Engine Is Running

The following is not required for normal operation, but if you want to verify that Sun Grid Engine is being used, add --mca ras_gridengine_verbose to the mpirun command line. For example:

% ./mpirun -np 4 -mca ras_gridengine_verbose 100 hostname
[mynode6:04234] ras:gridengine: JOB_ID: 28
[mynode6:04234] ras:gridengine: mynode6: PE_HOSTFILE shows slots=2
[mynode6:04234] ras:gridengine: mynode7: PE_HOSTFILE shows slots=2
mynode6
mynode6
mynode7
mynode7
%

To Start an Interactive Session Using qrsh

An alternate way to start an interactive session is by using qrsh instead of qsh. For example:

% qrsh -V -pe orte 8 mpirun -np 4 -byslot hostname

Using MPI Client/Server Applications

The instructions in this section explain how to get best results when starting Open MPI client/server applications.

To Launch the Client/Server Job

1. Type the following command to launch the server application. Substitute the name of your MPI job’s universe for univ1:

% ./mpirun -np 1 --universe univ1 t_accept

2. Type the following command to launch the client application, substituting the name of your MPI job’s universe for univ1:

% ./mpirun -np 4 --universe univ1 t_connect

If the client and server jobs span more than 1 node, the first job (that is, the server job) must specify on the mpirun command line all the nodes that will be used. Specifying the node names allocates the specified hosts from the entire universe of server and client jobs.

For example, if the server runs on node0 and the client job runs on node1 only, the command to launch the server must specify both nodes (using the -host node0,node1 flag) even it uses only one process on node0.

Assuming that the persistent daemon is started on node0, the command to launch the server would look like this:

node0% ./mpirun -np 1 --universe univ1 -host node0,node1 t_accept

The command to launch the client is:

node0% ./mpirun -np 4 --universe univ1 -host node1 t_connect

Using Name Publishing

If you are planning on using name publishing, you must perform some additional tasks. You need to start up an ompi-server processon your server so that both the clients andservers can exchange information using that server.

For information about how to start the ompi-server process, type the following command on your server:

% man ompi-server

Troubleshooting Client/Server Jobs

If the MPI client/server job fails to start, you might see error messages similar to this:

node0% ./orted --persistent --seed --scope public --universe univ4 --debug
[node0:21760] procdir: (null)
[node0:21760] jobdir: (null)
[node0:21760] unidir:
/tmp/openmpi-sessions-joeuser@node0_0/univ4
[node0:21760] top: openmpi-sessions-joeuser@node0_0
[node0:21760] tmp: /tmp
[node0:21760] orte_init: could not contact the specified
universe name univ4
[node0:21760] [NO-NAME] ORTE_ERROR_LOG: Unreachable in file
/opt/SUNWhpc/HPC8.1/sun/bin/orted/runtime/orte_init_stage1.c
at line 221

These messages indicate that there is residual data left in the /tmp directory. This can happen if a previous client/server job has already run from the same node.

To empty the /tmp directory, use the orte-clean utility. For more information about orte-clean, see the orte-clean man page.

You might also need to run orte-clean if you see error messages similar to the following:

node0% ./orted --persistent --seed --scope public --universe univ4 --debug
[node0:21760] procdir: (null)
[node0:21760] jobdir: (null)
[node0:21760] unidir:
/tmp/openmpi-sessions-joeuser@node0_0/univ4
[node0:21760] top: openmpi-sessions-joeuser@node0_0
[node0:21760] tmp: /tmp
[node0:21760] orte_init: could not contact the specified
universe name univ4
[node0:21760] [NO-NAME] ORTE_ERROR_LOG: Unreachable in file
/opt/SUNWhpc/HPC8.1/sun/bin/orted/runtime/orte_init_stage1.c
at line 221
----------------------------------------------------------------
It looks like orte_init failed for some reason; your parallel process is likely to abort.  There are many reasons that a parallel process can fail during orte_init; some of which are due to configuration or environment problems.  This failure appears to be an internal failure; here’s some additional information (which may only be relevant to an Open MPI developer):
   orte_sds_base_contact_universe failed
   --> Returned value -12 instead of ORTE_SUCCESS
----------------------------------------------------------------
[node0:21760] [NO-NAME] ORTE_ERROR_LOG: Unreachable in file
/opt/SUNWhpc/HPC8.1/sun/bin/orted/runtime/orte_system_init.c
at line 42
[node0:21760] [NO-NAME] ORTE_ERROR_LOG: Unreachable in file
/opt/SUNWhpc/HPC8.1/sun/bin/orte/runtime/orte_init.c
at line 52
Open RTE was unable to initialize properly.  The error occured while attempting to orte_init().  Returned value -12 instead of ORTE_SUCCESS.

Command Reference

This section provides a quick reference for the mpirun command options.

TABLE 5-2 `mpirun` Command Options
Option	Description
`-am` list-name	Use the MCA parameter set file list called list-name.
`--app` appfile	Directs `mpirun` to use the appfile specified by appfile and to ignore other programs specified on the command line
`-bynode` `--bynode`	Allocates (maps) the processes specified in a round-robin scheme by node. `-byslot` is the default (see below).
`-byslot` `--byslot`	Allocates (maps) the processes specified in a round-robin scheme by slot (processor) This is the default.
`-c` number	Same as the `-np` <number> option. Directs `mpirun` to run the number of copies (specified in number) of the specified program on the selected nodes. See the description of the `-np` option for more information.
-cf --cartofile filename	Run using the cartography file filename. Cartography files describe the layout of and connections between components in a cluster. For more information about cartography files, see the `mpirun(1)` man page.
`-debug` `--debug`	Invokes the user-level debugger specified in the MCA parameter `orte_base_user_debugger`. The default value for the MCA parameter is `totalview`. To change the specified debugger, change the value of the MCA parameter. (See Chapter 7 for more information.)
--debug-daemons	Enable debugging of any ORTE daemons used by this application.
-debug-daemons-file	Enable debugging of any OpenRTE daemons used by this application, storing output in files
--debug-devel	Enable debugging of OpenRTE.
`-debugger` `--debugger`	Specifies the sequence of debuggers you want to use with `mpirun`.This option is a synonym for the `orte_base_user_debugger`, and has the same default value. If you use this option, the value you specify overrides any value set in `orte_base_user_debugger`.
-default-hostfile --default-hostfile filename	Run using the provided default hostfile filename.
-display-allocation --display-allocation	Display the allocation being used by this job.
-display-devel-allocation	Intended for Open MPI/OpenRTE developers. Display a detailed list of the allocation being used by this job.
-display-map --display-map	Display the process map just before launch.
--display-devel-map	Intended for Open MPI/OpenRTE developers. Displayes a detailed process map just before launch.
--do-not-launch	Perform all necessary operations to prepare to launch the application, but do not actually launch it.
-do-not-resolve --do-not-resolve	Do not attempt to resolve interfaces.
`-gmca` `--gmca` param value	Specifies global MCA parameters. param is the name of the specified MCA parameter. value is the value for that parameter.
`-h` `--help`	Displays help for the `mpirun` command. When this option is specified on the command line, it overrides any other options and displays the command help.
`-H` host1, host2, ...hostn	Specifies the list of hosts on which to invoke processes. This is a synonym for `-host`.
`--hetero`	Indicates that multiple `app_context`s are being provided that are a mix of 32 - amd 64-bit binaries.
`-host` `--host` <host1,host2,...hostn>	Specifies the list of hosts on which to invoke processes. This is a synonym for `-H`.
`-hostfile` `--hostfile` filename	Directs mpirun to use the specified hostfile. If `-hostfile` is specified without using filename, `mpirun` uses the default hostfile located at `/opt/SUNWhpc/HPC8.1/etc/openmpi-default-hostfile`.
--launch-agent command-name	Command used to start processes on remote nodes (default: orted)
-leave-seeesion-attached	Enable debugging of OpenRTE.
-loadbalance --loadbalance	Balance total number of processes across all allocated nodes.
`-machinefile` `--machinefile` filename	Synonymous with `-hostfile`.
`-mca` `--mca` param value	Specifies an MCA parameter, where param is the name of the desired MCA parameter and value is the desired value for that parameter. These parameters and values are considered to be global parameters unless the `-gmca` option appears on the same command line.
`-n, --n` number	Specifies the number of processes to run. Synonymous with `-np`.
`--no-daemonize`	Keeps the ORTE daemons used by this application from being detached and used by other processes.
`-nolocal, --nolocal`	Specifies that MPI applications should not be run on the local node (the same node on which `mpirun` is running).
`-nooversubscribe` `--nooversubscribe`	Never oversubscribe the nodes, even if the system supports such operations. This option sets the effective value of `max_slots` to equal the value of `slots`, and overrides the settings for that node in the hostfile.
`--noprefix` value	Cancels any previously specified directory options specified by the `--prefix` option.
`-npernode --npernode`number	Launch number processes per node on all allocated nodes.
-ompi-server --ompi-server name	Specify the URL of the Open MPI server, or the name of the file (specified as file:filename) that contains that information needed to run the job.
`-path` `--path` pathname	Specifies to `mpirun` that the executables to be used for the current job are stored in pathname.
-pernode --pernode	Launch one process per available node on the number of nodes specified in the `-np` option. If no `-np` option is used, then use all allocated nodes.
`--prefix` pathname	Specifies the path to the directory where Open MPI is located on remote node(s). This option is used to run Open MPI on remote nodes (as opposed to running on the local node).
`--preload-files` filename	Preload the comma separated list of files (specified by filename) to the remote machine’s current working directory before starting the remote process.
`--preload-files-dest-dir` directory	Specifies the destination directory (specified by directory) that contains the list of files (specified by `--preload-files` filename) to be used with the `--preload-files` option. By default, this option uses both absolute and relative paths..
`-q, -quiet`	Suppresses output messages from Open MPI.
-rf, --rankfile filename	Provide a rankfile file.
`-s, --preload-binary`	Preload the binary on the remote machine before starting the remote process.
--server-wait-time seconds	Time in seconds to wait for ompi-server (default: 10 sec).
--slot-list id-list	List of processor IDs to which you want to bind MPI processes (for example, a list of processors used in conjunction with rankfile files)
`--tmpdir` pathname	Specifies the root for the session directory tree for `mpirun` only. This applies only to the current job.
`-tv, --tv`	Synonymous with `--debug`. This option is deprecated; use `--debug` instead, if possible.
`--universe` username@hostname:universe_name	Sets the Open MPI universe for this application to username@hostname:universe_name.
`-v, --verbose`	Specifies verbose output.
`-V, --version`	Displays the `mpirun` version number. If no other options are specified on the same command line, this option also causes `mpirun` to exit.
--wait-for-server	If ompi-server is not already running, wait until it is detected (default: false)
`-wd` directory-name	Change to the specified directory before executing the application.
`-wdir, --wdir`	Synonymous with `-wd`.
`-x` variable `-x` variable=value	Exports the environment variable variable and its value in the current environment to the started processes. If value is specified, the option sets the variable’s value to value in the started processes.
-xml, --xml	Provide all output in XML format.

For More Information

For more information about the mpirun command and its options, see the following:

Chapter 7, Using MCA Parameters With mpirun
the mpirun(3) man page
Open MPI FAQ at http://www.open-mpi.org

Name

orterun, mpirun, mpiexec - Execute serial and parallel jobs in Open MPI.

Note: mpirun, mpiexec, and orterun are all synonyms for each other. Using any of the names will produce the same behavior.

mpirun [ options ] <program> [ <args> ]

Multiple Instruction Multiple Data (MIMD) Model:

mpirun [ global_options ] [ local_options1 ]
<program1> [ <args1> ] : [ local_options2 ]
<program2> [ <args2> ] : ... :
[ local_optionsN ]
<programN> [ <argsN> ]

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

Quick Summary

If you are simply looking for how to run an MPI application, you probably want to use a command line of the following form:

% mpirun [ -np X ] [ --hostfile <filename> ] <program>

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.

Options

mpirun 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 details.

<program>: The program executable. This is identified as the first non-recognized argument to mpirun.
<args>: 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.
-h, --help: Display help for this command
-q, --quiet: Suppress informative messages from orterun during application execution.
-v, --verbose: Be verbose
-V, --version: 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. (deprecated in favor of --map-by ppr:n:socket)
-npernode, --npernode <#pernode>: On each node, launch this many processes. (deprecated in favor of --map-by ppr:n:node)
-pernode, --pernode: On each node, launch one process -- equivalent to -npernode 1. (deprecated in favor of --map-by ppr:1:node)

To map processes:

--map-by <foo>: Map to the specified object, defaults to socket. Supported options include slot, hwthread, core, L1cache, L2cache, L3cache, socket, numa, board, node, sequential, distance, and ppr. Any object can include modifiers by adding a : and any combination of PE=n (bind n processing elements to each proc), SPAN (load balance the processes across the allocation), OVERSUBSCRIBE (allow more processes on a node than processing elements), and NOOVERSUBSCRIBE. This includes PPR, where the pattern would be terminated by another colon to separate it from the modifiers.
-bycore, --bycore: Map processes by core (deprecated in favor of --map-by core)
-bysocket, --bysocket: Map processes by socket (deprecated in favor of --map-by socket)
-nolocal, --nolocal: 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.
-nooversubscribe, --nooversubscribe: 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 each node.
-bynode, --bynode: Launch processes one per node, cycling by node in a round-robin fashion. This spreads processes evenly among nodes and assigns MPI_COMM_WORLD ranks in a round-robin, "by node" manner.

To order processes’ ranks in MPI_COMM_WORLD:

--rank-by <foo>: Rank in round-robin fashion according to the specified object, defaults to slot. Supported options include slot, hwthread, core, socket, numa, board, and node.

For process binding:

--bind-to <foo>: Bind processes to the specified object, defaults to core. Supported options include slot, hwthread, core, socket, numa, board, and none.
-cpus-per-proc, --cpus-per-proc <#perproc>: Bind each process to the specified number of cpus. (deprecated in favor of --map-by <obj>:PE=n)
-cpus-per-rank, --cpus-per-rank <#perrank>: Alias for -cpus-per-proc. (deprecated in favor of --map-by <obj>:PE=n)
-bind-to-core, --bind-to-core: Bind processes to cores (deprecated in favor of --bind-to core)
-bind-to-socket, --bind-to-socket: Bind processes to processor sockets (deprecated in favor of --bind-to socket)
-bind-to-none, --bind-to-none: Do not bind processes (deprecated in favor of --bind-to none)
-report-bindings, --report-bindings: 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.

For rankfiles:

-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 processes to a process-unique version of the specified filename. Any directories in the filename will automatically be created. Each output file will consist of filename.id, where the id will be the processes’ rank in MPI_COMM_WORLD, left-filled with zero’s for correct ordering in listings.
-stdin, --stdin <rank>: The MPI_COMM_WORLD rank of the process that is to receive stdin. The default is to forward stdin to MPI_COMM_WORLD rank 0, but this option can be used to forward stdin to any process. It is also acceptable to specify none, indicating that no processes are to receive stdin.
-tag-output, --tag-output: Tag each line of output to stdout, stderr, and stddiag with [jobid, MCW_rank]<stdxxx> indicating the process jobid and MPI_COMM_WORLD rank of the process that generated the output, and the channel which generated it.
-timestamp-output, --timestamp-output: Timestamp each line of output to stdout, stderr, and stddiag.
-xml, --xml: Provide all output to stdout, stderr, and stddiag in an xml format.
-xterm, --xterm <ranks>: Display the output from the processes identified by their MPI_COMM_WORLD 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 process. Note: xterm will normally terminate the window upon termination of the process running within it. However, by adding a "!" to the end of the list of specified ranks, the proper options will be provided to ensure that xterm keeps the window open after the process terminates, thus allowing you to see the process’ output. Each xterm window will subsequently need to be manually closed. Note: 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< dir>: 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.
--preload-binary: 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-files <files>: 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.
--preload-files-dest-dir <path>: 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.
--tmpdir <dir>: Set the root for the session directory tree for mpirun only.
-wd <dir>: Synonym for -wdir.
-wdir <dir>: Change to the directory <dir> before the user’s program executes. See the "Current Working Directory" section for notes on relative paths. Note: If the -wdir option appears both on the command line and in an application context, the context will take precedence over the command line. Thus, if the path to the desired wdir is different on the backend nodes, then it must be specified as an absolute path that is correct for the backend node.
-x <env>: 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 example: % 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.

For debugging:

-debug, --debug: Invoke the user-level debugger indicated by the orte_base_user_debugger MCA parameter.
-debugger, --debugger: Sequence of debuggers to search for when --debug is used (i.e. a synonym for orte_base_user_debugger MCA parameter).
-tv, --tv: 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.
--app <appfile>: Provide an appfile, ignoring all other command line options.
-cf, --cartofile <cartofile>: Provide a cartography file.
--hetero: Indicates that multiple app_contexts are being provided that are a mix of 32/64-bit binaries.
-leave-session-attached, --leave-session-attached: 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 mpirun to be used as the server) , the name of the file (specified as file:filename) that contains that info, or the PID (specified as pid:#) of the mpirun to be used as the server.
The Open MPI server is used to support multi-application data exchange via the MPI-2 MPI_Publish_name and MPI_Lookup_name functions.
-report-pid, --report-pid <channel>: Print out mpirun’s PID during startup. The channel must be either a ’-’ to indi cate that the pid is to be output to stdout, a ’+’ to indicate that the pid is to be outp ut to stderr, or a filename to which the pid is to be written.
-report-uri, --report-uri <channel>: Print out mpirun’s URI during startup. The channel must be either a ’-’ to indi cate that the URI is to be output to stdout, a ’+’ to indicate that the URI is to be outp ut to stderr, or a filename to which the URI is to be written.
-wait-for-server, --wait-for-server: 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:

-d, --debug-devel: Enable debugging of the OmpiRTE (the run-time layer in Open MPI). This is not generally useful for most users.
--debug-daemons: Enable debugging of any OmpiRTE daemons used by this application.
--debug-daemons-file: Enable debugging of any OmpiRTE daemons used by this application, storing output in files.
-launch-agent, --launch-agent: 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.
--noprefix: Disable the automatic --prefix behavior

There may be other options listed with mpirun --help.

Environment Variables

MPIEXEC_TIMEOUT: The maximum number of seconds that mpirun (mpiexec) will run. After this many seconds, mpirun will abort the launched job and exit.

Description

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 (e.g. -np).

Specifying Host Nodes

Host nodes can be identified on the mpirun command line with the -host option or in a hostfile.

For example,

mpirun -H aa,aa,bb ./a.out: launches two processes on node aa and one on bb.

Or, consider the hostfile

% cat myhostfile
aa slots=2
bb slots=2
cc slots=2

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
aa slots=4
bb slots=4
cc slots=4

Now,

mpirun -hostfile myhostfile -np 6 ./a.out: will launch processes 0-3 on node aa and processes 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 processes 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 -bynode 0 3 1 4 2 5

mpirun -nolocal 0 1 2 3 4 5

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 hostfile:

mpirun -hostfile myhostfile -np 14 -nooversubscribe ./a.out: 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
bb max_slots=4
cc 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.

And here is a MIMD example:

mpirun -H aa -np 1 hostname : -H bb,cc -np 2 uptime: 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 processes 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 as before

mpirun -hostfile myhostfile ./a.out: will launch three processes, on nodes 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 rankfile, which gives you detailed control over process binding as well. Rankfiles are discussed below.

Process Binding

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 ... -bysocket -bind-to-socket
[...] ... binding child [...,0] to socket 0 cpus 000f
[...] ... binding child [...,1] to socket 1 cpus 00f0
[...] ... binding child [...,2] to socket 0 cpus 000f
[...] ... binding child [...,3] to socket 1 cpus 00f0

% 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 bound 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, certain process binding options 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:

mpirun option MCA parameter key value

-bycore rmaps_base_schedule_policy core
-bysocket rmaps_base_schedule_policy socket
-bind-to-core orte_process_binding core
-bind-to-socket orte_process_binding socket
-bind-to-none orte_process_binding none

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

% cat $HOME/.openmpi/mca-params.conf
rmaps_base_schedule_policy = socket
orte_process_binding = socket:if-avail

Rankfiles

Rankfiles are text files that specify detailed information about how individual processes should be mapped to nodes, and to which processor(s) they should be bound. Each line of a rankfile specifies the location of one process (for MPI jobs, the process’ "rank" refers to its rank in MPI_COMM_WORLD). The general form of each line in the rankfile is:

rank <N>=<hostname> slot=<slot list>

For example:

$ cat myrankfile
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

Means that

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.

The hostnames listed above are "absolute," meaning that actual resolveable hostnames are specified. However, hostnames can also be specified as "relative," meaning that they are specified in relation to an externally-specified list of hostnames (e.g., by mpirun’s --host argument, a hostfile, or a job scheduler).

The "relative" specification is of the form "+n<X>", where X is an integer specifying the Xth hostname in the set of all available hostnames, indexed from 0. For example:

$ cat myrankfile
rank 0=+n0 slot=1:0-2
rank 1=+n1 slot=0:0,1
rank 2=+n2 slot=1-2
$ mpirun -H aa,bb,cc,dd -rf myrankfile ./a.out

Starting with Open MPI v1.7, all socket/core slot locations are be specified as logical indexes (the Open MPI v1.6 series used physical indexes). You can use tools such as HWLOC’s "lstopo" to find the logical indexes of socket and cores.

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.

Locating Files

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 source node(s).

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 applications.

If the -wdir option appears both in a context file and on the command line, the context file directory will override the command line value.

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 the starter.

All directory changing occurs before the user’s program is invoked; it does not wait until MPI_INIT is called.

Standard I/O

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. Note: 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 mpirun. 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.

Signal Propagation

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 SIGKILL.

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 by orterun.

Process Termination / Signal Handling

During the run of an MPI application, if any process 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 MPI application.

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 MPI_THREAD_MULTIPLE 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.

Process Environment

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.

Remote Execution

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:

Local bindir:: /local/node/directory/bin
Local libdir:: /local/node/directory/lib64

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.

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 passed. For example:

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 allocated node.

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:

OMPI_MCA_<key>=<value>

Thus, the -mca switch overrides any previously set environment variables. The -mca settings similarly override MCA parameters set in the $OPAL_PREFIX/etc/openmpi-mca-params.conf or $HOME/.openmpi/mca-params.conf file.

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.

Exit status

There is no standard definition for what mpirun should return as an exit status. After considerable discussion, we settled on the following method for assigning the mpirun exit status (note: in the following description, the "primary" job is the initial application started by mpirun - all jobs that are spawned by that job are designated "secondary" jobs):

[bu]: if all processes in the primary job normally terminate with exit status 0, we return 0
[bu]: if one or more processes in the primary job normally terminate with non-zero exit status, we return the exit status of the process with the lowest MPI_COMM_WORLD rank to have a non-zero status
[bu]: if all processes in the primary job normally terminate with exit status 0, and one or more processes in a secondary job normally terminate with non-zero exit status, we (a) return the exit status of the process with the lowest MPI_COMM_WORLD rank in the lowest jobid to have a non-zero status, and (b) output a message summarizing the exit status of the primary and all secondary jobs.
[bu]: if the cmd line option --report-child-jobs-separately is set, we will return -only- the exit status of the primary job. Any non-zero exit status in secondary jobs will be reported solely in a summary print statement.

By default, OMPI records and notes that MPI processes exited with non-zero termination status. This is generally not considered an "abnormal termination" - i.e., OMPI will not abort an MPI job if one or more processes return a non-zero status. Instead, the default behavior simply reports the number of processes terminating with non-zero status upon completion of the job.

However, in some cases it can be desirable to have the job abort when any process terminates with non-zero status. For example, a non-MPI job might detect a bad result from a calculation and want to abort, but doesn’t want to generate a core file. Or an MPI job might continue past a call to MPI_Finalize, but indicate that all processes should abort due to some post-MPI result.

It is not anticipated that this situation will occur frequently. However, in the interest of serving the broader community, OMPI now has a means for allowing users to direct that jobs be aborted upon any process exiting with non-zero status. Setting the MCA parameter "orte_abort_on_non_zero_status" to 1 will cause OMPI to abort all processes once any process exits with non-zero status.

Terminations caused in this manner will be reported on the console as an "abnormal termination", with the first process to so exit identified along with its exit status.

Examples

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 parameters.

Return Value

mpirun returns 0 if all processes 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 processes 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 processes exit before calling MPI_FINALIZE, the return value of the MPI_COMM_WORLD 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 process that died but is not guaranteed to be so.

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