MPIRUN(1) Open MPI MPIRUN(1)
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 equiva-
lent to the directory where mpirun resides, minus its last subdirec-
tory. 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 proba-
bly 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 environ-
ment (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 speci-
fied 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 proces-
sor cores on the node, and use that as the number of slots avail-
able.
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 man-
ager. 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 re-
source manager) if oversubscription is enabled (by default, it is dis-
abled). Most MPI applications and HPC environments do not oversub-
scribe; 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 avail-
able. 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 com-
mand 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 fur-
ther 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 con-
text 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 ma-
chine (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 modi-
fied by the following options) at the very beginning of execution, re-
gardless 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 be-
havior in prior releases where daemons were only launched after mapping
was complete, and thus only occurred on nodes where application pro-
cesses 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., re-
questing 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 pro-
gram 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 auto-
matically 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) other-
wise.
—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 op-
tions 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 (al-
low 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 mecha-
nism.
-nooversubscribe, --nooversubscribe
Do not oversubscribe any nodes; error (without starting any pro-
cesses) if the requested number of processes would cause over-
subscription. 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 sys-
tem, 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. Sup-
ported 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 directo-
ries in the filename will automatically be created. Each output
file will consist of filename.id, where the id will be the pro-
cesses' rank in MPI_COMM_WORLD, left-filled with zero's for cor-
rect ordering in listings. A relative path value will be con-
verted to an absolute path based on the cwd where mpirun is exe-
cuted. 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 [jo-
bid, 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 for-
mat.
-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 indi-
cating 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 op-
tions 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 re-
spond 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 set-
ting.
--prefix <dir>
Prefix directory that will be used to set the PATH and LD_LI-
BRARY_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 ses-
sion directory.
-wd <dir>
Synonym for -wdir.
-wdir <dir>
Change to the directory <dir> before the user's program exe-
cutes. 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 de-
fine) 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 en-
vironment 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, espe-
cially 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 sec-
onds, mpirun will abort the launched job and exit with a non-
zero exit status. Using --timeout can be also useful when com-
bined with the --get-stack-traces option.
-tv, --tv
Launch processes under the TotalView debugger. Deprecated back-
wards 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 de-
faults 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 appli-
cation, 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 al-
lows error messages from the daemons as well as the underlying
environment (e.g., when failing to launch a daemon) to be out-
put.
-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:file-
name) 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 con-
tainers 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 ei-
ther 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 ei-
ther 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 de-
fault 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 applica-
tion.
--debug-daemons-file
Enable debugging of any OmpiRTE daemons used by this applica-
tion, 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 al-
lows 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 ex-
pires.
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 ap-
plication can be specified on the mpirun command line.
If the application is multiple instruction multiple data (MIMD), com-
prising of multiple programs, the set of programs and argument can be
specified in one of two ways: Extended Command Line Arguments, and Ap-
plication Context.
An application context describes the MIMD program set including all ar-
guments 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 appli-
cation 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 spe-
cific 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 op-
tions 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 oversubscrip-
tion.
Limits to oversubscription can also be specified in the hostfile it-
self:
% 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 re-
maining 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 cur-
rently does not get "max_slots" values from the resource manager.
Of course, -np can also be used with the -H or -host option. For exam-
ple,
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 loca-
tions 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 sequen-
tially 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, re-
spectively. 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 be-
ginning.
The binding phase actually binds each process to a given set of proces-
sors. 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 ap-
plication performance is sensitive to interprocess communication costs.
Binding can also keep the operating system from migrating processes ex-
cessively, 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 as-
signed 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, con-
sider 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 as-
sign 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 com-
prised 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 in-
dicated that each slot (i.e., process) should consume two processor el-
ements. 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 oper-
ating 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 alterna-
tively in a system or user mca-params.conf file or as environment vari-
ables, 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 proces-
sor(s) they should be bound. Each line of a rankfile specifies the lo-
cation 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 loca-
tions. 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 resolve-
able hostnames are specified. However, hostnames can also be specified
as "relative," meaning that they are specified in relation to an exter-
nally-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 in-
teger specifying the Xth hostname in the set of all available host-
names, 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 logi-
cal 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 ini-
tial working directory determined by the specific starter used. For ex-
ample 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 directo-
ries 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 ex-
cept the MPI_COMM_WORLD rank 0 process. The MPI_COMM_WORLD rank 0
process inherits standard input from mpirun. Note: The node that in-
voked 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 buf-
fer 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 environ-
ment 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_LI-
BRARY_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 ex-
ecutables 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 cur-
rent environment has PATH and/or LD_LIBRARY_PATH set properly, the re-
mote 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 (espe-
cially to find the shared libraries required to run user MPI applica-
tions).
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 pro-
vided 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 direc-
tory to set the remote PATH and LD_LIBRARY_PATH before executing any
Open MPI or user applications. This allows running Open MPI jobs with-
out 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 direc-
tory 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_LI-
BRARY_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 "/re-
mote/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 com-
mon prefix.
Note that executing mpirun via an absolute pathname is equivalent to
specifying --prefix without the last subdirectory in the absolute path-
name 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 auto-
matically 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 ex-
ample. While the syntax of the -x option and MCA param allows the defi-
nition 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 (Modu-
lar 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 param-
eters to pass to that BTL, etc.).
The -mca switch takes two arguments: <key> and <value>. The <key> ar-
gument 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 sin-
gle 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 correspond-
ing environment variables before running mpirun. The form of the envi-
ronment variables that Open MPI sets is:
OMPI_MCA_<key>=<value>
Thus, the -mca switch overrides any previously set environment vari-
ables. 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 spe-
cific 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 informa-
tion on the command.
Setting MCA parameters and environment variables from file.
The -tune command line option and its synonym -mca mca_base_en-
var_file_prefix allows a user to set mca parameters and environment
variables with the syntax described below. This option requires a sin-
gle 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 be-
havior as --allow-run-as-root in order to stress the Open MPI team's
strong advice against running as the root user. After extended discus-
sions with communities who use containers (where running as the root
user is the default), there was a persistent desire to be able to en-
able root execution of mpirun via an environmental control (vs. the ex-
isting --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 de-
scription, the "primary" job is the initial application started by
mpirun - all jobs that are spawned by that job are designated "sec-
ondary" jobs):
• if all processes in the primary job normally terminate with exit sta-
tus 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 sta-
tus 0, and one or more processes in a secondary job normally termi-
nate 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 re-
port 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 oc-
curred in mpirun, or one or more processes exited before calling
MPI_FINALIZE. If an internal error occurred in mpirun, the correspond-
ing 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 be-
fore 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)
4.1.4 May 26, 2022 MPIRUN(1)
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