oracular (1) mpirun.openmpi.1.gz
NAME
orterun, mpirun, mpiexec - Execute serial and parallel jobs in Open MPI. oshrun, shmemrun - Execute
serial and parallel jobs in Open SHMEM.
Note: mpirun, mpiexec, and orterun are all synonyms for each other as well as oshrun, shmemrun in case
Open SHMEM is installed. Using any of the names will produce the same behavior.
SYNOPSIS
Single Process Multiple Data (SPMD) Model:
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.
Please note that mpirun automatically binds processes as of the start of the v1.8 series. Three binding
patterns are used in the absence of any further directives:
Bind to core: when the number of processes is <= 2
Bind to socket: when the number of processes is > 2
Bind to none: when oversubscribed
If your application uses threads, then you probably want to ensure that you are either not bound at all
(by specifying --bind-to none), or bound to multiple cores using an appropriate binding level or specific
number of processing elements per application process.
DEFINITION OF 'SLOT'
The term "slot" is used extensively in the rest of this manual page. A slot is an allocation unit for a
process. The number of slots on a node indicate how many processes can potentially execute on that node.
By default, Open MPI will allow one process per slot.
If Open MPI is not explicitly told how many slots are available on a node (e.g., if a hostfile is used
and the number of slots is not specified for a given node), it will determine a maximum number of slots
for that node in one of two ways:
1. Default behavior
By default, Open MPI will attempt to discover the number of processor cores on the node, and use that
as the number of slots available.
2. When --use-hwthread-cpus is used
If --use-hwthread-cpus is specified on the mpirun command line, then Open MPI will attempt to discover
the number of hardware threads on the node, and use that as the number of slots available.
This default behavior also occurs when specifying the -host option with a single host. Thus, the
command:
mpirun --host node1 ./a.out
launches a number of processes equal to the number of cores on node node1, whereas:
mpirun --host node1 --use-hwthread-cpus ./a.out
launches a number of processes equal to the number of hardware threads on node1.
When Open MPI applications are invoked in an environment managed by a resource manager (e.g., inside of a
SLURM job), and Open MPI was built with appropriate support for that resource manager, then Open MPI will
be informed of the number of slots for each node by the resource manager. For example:
mpirun ./a.out
launches one process for every slot (on every node) as dictated by the resource manager job
specification.
Also note that the one-process-per-slot restriction can be overridden in unmanaged environments (e.g.,
when using hostfiles without a resource manager) if oversubscription is enabled (by default, it is
disabled). Most MPI applications and HPC environments do not oversubscribe; for simplicity, the majority
of this documentation assumes that oversubscription is not enabled.
Slots are not hardware resources
Slots are frequently incorrectly conflated with hardware resources. It is important to realize that
slots are an entirely different metric than the number (and type) of hardware resources available.
Here are some examples that may help illustrate the difference:
1. More processor cores than slots
Consider a resource manager job environment that tells Open MPI that there is a single node with 20
processor cores and 2 slots available. By default, Open MPI will only let you run up to 2 processes.
Meaning: you run out of slots long before you run out of processor cores.
2. More slots than processor cores
Consider a hostfile with a single node listed with a "slots=50" qualification. The node has 20
processor cores. By default, Open MPI will let you run up to 50 processes.
Meaning: you can run many more processes than you have processor cores.
DEFINITION OF 'PROCESSOR ELEMENT'
By default, Open MPI defines that a "processing element" is a processor core. However, if --use-
hwthread-cpus is specified on the mpirun command line, then a "processing element" is a hardware thread.
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.
-N <num>
Launch num processes per node on all allocated nodes (synonym for npernode).
-display-map, --display-map
Display a table showing the mapped location of each process prior to launch.
-display-allocation, --display-allocation
Display the detected resource allocation.
-output-proctable, --output-proctable
Output the debugger proctable after launch.
-dvm, --dvm
Create a persistent distributed virtual machine (DVM).
-max-vm-size, --max-vm-size <size>
Number of processes to run.
-novm, --novm
Execute without creating an allocation-spanning virtual machine (only start daemons on nodes
hosting application procs).
-hnp, --hnp <arg0>
Specify the URI of the Head Node Process (HNP), or the name of the file (specified as
file:filename) that contains that info.
Use one of the following options to specify which hosts (nodes) of the cluster to run on. Note that as of
the start of the v1.8 release, mpirun will launch a daemon onto each host in the allocation (as modified
by the following options) at the very beginning of execution, regardless of whether or not application
processes will eventually be mapped to execute there. This is done to allow collection of hardware
topology information from the remote nodes, thus allowing us to map processes against known topology.
However, it is a change from the behavior in prior releases where daemons were only launched after
mapping was complete, and thus only occurred on nodes where application processes would actually be
executing.
-H, -host, --host <host1,host2,...,hostN>
List of hosts on which to invoke processes.
-hostfile, --hostfile <hostfile>
Provide a hostfile to use.
-default-hostfile, --default-hostfile <hostfile>
Provide a default hostfile.
-machinefile, --machinefile <machinefile>
Synonym for -hostfile.
-cpu-set, --cpu-set <list>
Restrict launched processes to the specified logical cpus on each node (comma-separated list).
Note that the binding options will still apply within the specified envelope - e.g., you can elect
to bind each process to only one cpu within the specified cpu set.
The following options specify the number of processes to launch. Note that none of the options imply a
particular binding policy - e.g., requesting N processes for each socket does not imply that the
processes will be bound to the socket.
-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.
—map-by ppr:N:<object>
Launch N times the number of objects of the specified type on each node.
-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)
-byslot, --byslot
Map and rank processes round-robin by slot.
-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. (Enabled by default).
-oversubscribe, --oversubscribe
Nodes are allowed to be oversubscribed, even on a managed system, and overloading of processing
elements.
-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.
-cpu-list, --cpu-list <cpus>
Comma-delimited list of processor IDs to which to bind processes [default=NULL]. Processor IDs
are interpreted as hwloc logical core IDs. Run the hwloc lstopo(1) command to see a list of
available cores and their logical IDs.
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, L1cache, L2cache, L3cache, 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, l1cache, l2cache, l3cache, socket, numa, board, cpu-list, 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)
-report-bindings, --report-bindings
Report any bindings for launched processes.
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. A relative path value will be converted
to an absolute path based on the cwd where mpirun is executed. Note that this will not work on
environments where the file system on compute nodes differs from that where mpirun is executed.
-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.
-merge-stderr-to-stdout, --merge-stderr-to-stdout
Merge stderr to stdout for each process.
-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.
-xml-file, --xml-file <filename>
Provide all output in XML format to the specified file.
-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.
--noprefix
Disable the automatic --prefix behavior
-s, --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.
-set-cwd-to-session-dir, --set-cwd-to-session-dir
Set the working directory of the started processes to their session directory.
-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.
-am <arg0>
Aggregate MCA parameter set file list.
-tune, --tune <tune_file>
Specify a tune file to set arguments for various MCA modules and environment variables. See the
"Setting MCA parameters and environment variables from file" section, below.
For debugging:
-debug, --debug
Invoke the user-level debugger indicated by the orte_base_user_debugger MCA parameter.
--get-stack-traces
When paired with the --timeout option, mpirun will obtain and print out stack traces from all
launched processes that are still alive when the timeout expires. Note that obtaining stack
traces can take a little time and produce a lot of output, especially for large process-count
jobs.
-debugger, --debugger <args>
Sequence of debuggers to search for when --debug is used (i.e. a synonym for
orte_base_user_debugger MCA parameter).
--timeout <seconds>
The maximum number of seconds that mpirun (also known as mpiexec, oshrun, orterun, etc.) will
run. After this many seconds, mpirun will abort the launched job and exit with a non-zero exit
status. Using --timeout can be also useful when combined with the --get-stack-traces option.
-tv, --tv
Launch processes under the TotalView debugger. Deprecated backwards compatibility flag. Synonym
for --debug.
There are also other options:
--allow-run-as-root
Allow mpirun to run when executed by the root user (mpirun defaults to aborting when launched as
the root user). Be sure to see the Running as root section, below, for more detail.
--app <appfile>
Provide an appfile, ignoring all other command line options.
-cf, --cartofile <cartofile>
Provide a cartography file.
-continuous, --continuous
Job is to run until explicitly terminated.
-disable-recovery, --disable-recovery
Disable recovery (resets all recovery options to off).
-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.
-enable-recovery, --enable-recovery
Enable recovery from process failure [Default = disabled].
-index-argv-by-rank, --index-argv-by-rank
Uniquely index argv[0] for each process using its rank.
-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.
-max-restarts, --max-restarts <num>
Max number of times to restart a failed process.
-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.
-personality, --personality <list>
Comma-separated list of programming model, languages, and containers being used (default="ompi").
--ppr <list>
Comma-separated list of number of processes on a given resource type [default: none].
-report-child-jobs-separately, --report-child-jobs-separately
Return the exit status of the primary job only.
-report-events, --report-events <URI>
Report events to a tool listening at the specified URI.
-report-pid, --report-pid <channel>
Print out mpirun's PID during startup. The channel must be either a '-' to indicate that the pid
is to be output to stdout, a '+' to indicate that the pid is to be output 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 indicate that the URI
is to be output to stdout, a '+' to indicate that the URI is to be output to stderr, or a filename
to which the URI is to be written.
-show-progress, --show-progress
Output a brief periodic report on launch progress.
-terminate, --terminate
Terminate the DVM.
-use-hwthread-cpus, --use-hwthread-cpus
Use hardware threads as independent CPUs.
Note that if a number of slots is not provided to Open MPI (e.g., via the "slots" keyword in a
hostfile or from a resource manager such as SLURM), the use of this option changes the default
calculation of number of slots on a node. See "DEFINITION OF 'SLOT'", above.
Also note that the use of this option changes the Open MPI's definition of a "processor element"
from a processor core to a hardware thread. See "DEFINITION OF 'PROCESSOR ELEMENT'", above.
-use-regexp, --use-regexp
Use regular expressions for launch.
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.
-display-devel-allocation, --display-devel-allocation
Display a detailed list of the allocation being used by this job.
-display-devel-map, --display-devel-map
Display a more detailed table showing the mapped location of each process prior to launch.
-display-diffable-map, --display-diffable-map
Display a diffable process map just before launch.
-display-topo, --display-topo
Display the topology as part of the process map just before launch.
-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.
--report-state-on-timeout
When paired with the --timeout command line option, report the run-time subsystem state of each
process when the timeout expires.
There may be other options listed with mpirun --help.
Environment Variables
MPIEXEC_TIMEOUT
Synonym for the --timeout command line option.
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.
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.
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.
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 --map-by node 0 3 1 4 2 5
mpirun -nolocal 0 1 2 3 4 5
The --map-by node option will load balance the processes across the available nodes, numbering each
process 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, Ranking, and Binding: Oh My!
Open MPI employs a three-phase procedure for assigning process locations and ranks:
mapping Assigns a default location to each process
ranking Assigns an MPI_COMM_WORLD rank value to each process
binding Constrains each process to run on specific processors
The mapping step is used to assign a default location to each process based on the mapper being employed.
Mapping by slot, node, and sequentially results in the assignment of the processes to the node level. In
contrast, mapping by object, allows the mapper to assign the process to an actual object on each node.
Note: the location assigned to the process is independent of where it will be bound - the assignment is
used solely as input to the binding algorithm.
The mapping of process processes to nodes can be defined 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 -mca rmaps seq ./a.out
will launch three processes, one on each of 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.
The second phase focuses on the ranking of the process within the job's MPI_COMM_WORLD. Open MPI
separates this from the mapping procedure to allow more flexibility in the relative placement of MPI
processes. This is best illustrated by considering the following two cases where we used the —map-by
ppr:2:socket option:
node aa node bb
rank-by core 0 1 ! 2 3 4 5 ! 6 7
rank-by socket 0 2 ! 1 3 4 6 ! 5 7
rank-by socket:span 0 4 ! 1 5 2 6 ! 3 7
Ranking by core and by slot provide the identical result - a simple progression of MPI_COMM_WORLD ranks
across each node. Ranking by socket does a round-robin ranking within each node until all processes have
been assigned an MCW rank, and then progresses to the next node. Adding the span modifier to the ranking
directive causes the ranking algorithm to treat the entire allocation as a single entity - thus, the MCW
ranks are assigned across all sockets before circling back around to the beginning.
The binding phase actually binds each process to a given set of processors. 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.
The processors to be used for binding can be identified in terms of topological groupings - e.g., binding
to an l3cache will bind each process to all processors within the scope of a single L3 cache within their
assigned location. Thus, if a process is assigned by the mapper to a certain socket, then a —bind-to
l3cache directive will cause the process to be bound to the processors that share a single L3 cache
within that socket.
Alternatively, processes can be assigned to processors based on their local rank on a node using the
--bind-to cpu-list:ordered option with an associated --cpu-list "0,2,5". In this example, the first
process on a node will be bound to cpu 0, the second process on the node will be bound to cpu 2, and the
third process on the node will be bound to cpu 5. --bind-to will also accept cpulist:ortered as a synonym
to cpu-list:ordered. Note that an error will result if more processes are assigned to a node than cpus
are provided.
To help balance loads, the binding directive uses a round-robin method when binding to levels lower than
used in the mapper. For example, consider the case where a job is mapped to the socket level, and then
bound to core. Each socket will have multiple cores, so if multiple processes are mapped to a given
socket, the binding algorithm will assign each process located to a socket to a unique core in a round-
robin manner.
Alternatively, processes mapped by l2cache and then bound to socket will simply be bound to all the
processors in the socket where they are located. In this manner, users can exert detailed control over
relative MCW rank location and binding.
Finally, --report-bindings can be used to report bindings.
As an example, consider a node with two processor sockets, each comprised of four cores, and each of
those cores contains one hardware thread. We run mpirun with -np 4 --report-bindings and the following
additional options:
% mpirun ... --map-by core --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 ... --map-by socket --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 ... --map-by slot:PE=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. Specifically, the mapping
by slot with the PE=2 qualifier indicated that each slot (i.e., process) should consume two processor
elements. Since --use-hwthread-cpus was not specified, Open MPI defined "processor element" as "core",
and therefore the --bind-to core caused each process to be bound to both of the cores to which it was
mapped.
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. Some examples include:
mpirun option MCA parameter key value
--map-by core rmaps_base_mapping_policy core
--map-by socket rmaps_base_mapping_policy socket
--rank-by core rmaps_base_ranking_policy core
--bind-to core hwloc_base_binding_policy core
--bind-to socket hwloc_base_binding_policy socket
--bind-to none hwloc_base_binding_policy none
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 logical socket 1, cores 0-2.
Rank 1 runs on node bb, bound to logical socket 0, cores 0 and 1.
Rank 2 runs on node cc, bound to logical cores 1 and 2.
Rankfiles can alternatively be used to specify physical processor locations. In this case, the syntax is
somewhat different. Sockets are no longer recognized, and the slot number given must be the number of the
physical PU as most OS's do not assign a unique physical identifier to each core in the node. Thus, a
proper physical rankfile looks something like the following:
$ cat myphysicalrankfile
rank 0=aa slot=1
rank 1=bb slot=8
rank 2=cc slot=6
This means that
Rank 0 will run on node aa, bound to the core that contains physical PU 1
Rank 1 will run on node bb, bound to the core that contains physical PU 8
Rank 2 will run on node cc, bound to the core that contains physical PU 6
Rankfiles are treated as logical by default, and the MCA parameter rmaps_rank_file_physical must be set
to 1 to indicate that the rankfile is to be considered as physical.
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.
A SIGTSTOP signal to mpirun will 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
LD_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. Environmental parameters can also be set/forwarded to the new
processes using the MCA parameter mca_base_env_list. The -x option to mpirun has been deprecated, but the
syntax of the MCA param follows that prior example. While the syntax of the -x option and MCA param
allows the definition of new variables, note that the parser for these options are currently not very
sophisticated - it does not even understand quoted values. Users are advised to set variables in the
environment and use the option 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.
Setting MCA parameters and environment variables from file.
The -tune command line option and its synonym -mca mca_base_envar_file_prefix allows a user to set mca
parameters and environment variables with the syntax described below. This option requires a single file
or list of files separated by "," to follow.
A valid line in the file may contain zero or many "-x", "-mca", or “--mca” arguments. The following
patterns are supported: -mca var val -mca var "val" -x var=val -x var. If any argument is duplicated in
the file, the last value read will be used.
MCA parameters and environment specified on the command line have higher precedence than variables
specified in the file.
Running as root
The Open MPI team strongly advises against executing mpirun as the root user. MPI applications should be
run as regular (non-root) users.
Reflecting this advice, mpirun will refuse to run as root by default. To override this default, you can
add the --allow-run-as-root option to the mpirun command line, or you can set the environmental
parameters OMPI_ALLOW_RUN_AS_ROOT=1 and OMPI_ALLOW_RUN_AS_ROOT_CONFIRM=1. Note that it takes setting two
environment variables to effect the same behavior as --allow-run-as-root in order to stress the Open MPI
team's strong advice against running as the root user. After extended discussions with communities who
use containers (where running as the root user is the default), there was a persistent desire to be able
to enable root execution of mpirun via an environmental control (vs. the existing --allow-run-as-root
command line parameter). The compromise of using two environment variables was reached: it allows root
execution via an environmental control, but it conveys the Open MPI team's strong recomendation against
this behavior.
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):
• if all processes in the primary job normally terminate with exit status 0, we return 0
• 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
• 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.
• 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, the job will abort when any process terminates with non-zero status. The MCA parameter
"orte_abort_on_non_zero_status" can be set to "false" (or "0") to cause OMPI to not abort a job if one or
more processes return a non-zero status. In that situation the OMPI records and notes that processes
exited with non-zero termination status to report the approprate exit status of mpirun (per bullet points
above).
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.
If the --timeout command line option is used and the timeout expires before the job completes (thereby
forcing mpirun to kill the job) mpirun will return an exit status equivalent to the value of ETIMEDOUT
(which is typically 110 on Linux and OS X systems).
SEE ALSO
MPI_Init_thread(3)