32.4.1 Starting Parallel ANSYS FLUENT on a Linux/UNIX System Using Command Line Options

To start the parallel version of ANSYS FLUENT using command line options, you can use the following syntax in a command prompt window:

fluent version -t nprocs [-p interconnect ] [-mpi= mpi_type ] -cnf= hosts_file

where

• version must be replaced by the version of ANSYS FLUENT you want to run ( 2d, 3d, 2ddp, or 3ddp).

• -p interconnect (optional) specifies the type of interconnect. The ethernet interconnect is used by default if the option is not explicitly specified. See Table  32.4.1, Table  32.4.2, and Table  32.4.3 for more information.

• -mpi= mpi_type (optional) specifies the type of MPI. If the option is not specified, the default MPI for the given interconnect will be used (the use of the default MPI is recommended). The available MPIs for Linux/UNIX are shown in Table  32.4.2.

• -cnf= hosts_file specifies the hosts file, which contains a list of the computers on which you want to run the parallel job. If the hosts file is not located in the directory where you are typing the startup command, you will need to supply the full pathname to the file.

  You can use a plain text editor to create the hosts file. The only restriction on the filename is that there should be no spaces in it. For example, hosts.txt is an acceptable hosts file name, but my hosts.txt is not.

  Your hosts file (e.g., hosts.txt) might contain the following entries:

  computer1
  computer2
  

  The last entry must be followed by a blank line.

  If a computer in the network is a multiprocessor, you can list it more than once. For example, if computer1 has 2 CPUs, then, to take advantage of both CPUs, the hosts.txt file should list computer1 twice:

  computer1
  computer1
  computer2
  

• -t nprocs specifies the number of processes to use. When the -cnf option is present, the hosts_file argument is used to determine which computers to use for the parallel job. For example, if there are 10 computers listed in the hosts file and you want to run a job with 5 processes, set nprocs to 5 (i.e., -t5) and ANSYS FLUENT will use the first 5 machines listed in the hosts file.

For example, to use the Infiniband interconnect, and to start the 3D solver with 4 compute nodes on the machines defined in the text file called fluent.hosts, you can enter the following in the command prompt:

fluent 3d -t4 -pinfiniband -cnf=fluent.hosts

Note that if the optional -cnf= hosts_file is specified, a compute node will be spawned on each machine listed in the file hosts_file. (If you enter this optional argument, do not include the square brackets.)

Also, ANSYS FLUENT provides a fault-tolerance feature on Infiniband Linux clusters running OFED. To invoke this feature, use the command line flag -pinfiniband.ofedft (or -pib.ofedft) which enables transparent port fail-over and high-availability features using HP-MPI. Note that while the simulations proceed more robustly with this option, there may be some degradation in performance.

The supported interconnects for parallel Linux/UNIX machines are listed below (Table  32.4.1, Table  32.4.2, and Table  32.4.3), along with their associated communication libraries, the corresponding syntax, and the supported architectures:

Table 32.4.1: Supported Interconnects for Linux/UNIX Platforms (Per Platform)

Platform	Processor	Architecture	Interconnects/Systems*
Linux	32-bit 64-bit 64-bit Itanium	lnx86 lnamd64 lnia64	ethernet, infiniband, myrinet ethernet, infiniband, myrinet ethernet, infiniband, myrinet, altix
Sun	64-bit	ultra_64	vendor** (default), ethernet
HP	64-bit Itanium	hpux11_ia64	vendor** (default), ethernet
IBM	64-bit	aix51_64	vendor** (default), ethernet

(*) Node processes on the same machine communicate by shared memory. ANSYS FLUENT lets the MPI autoselect the best interconnect available on the system. Users can specify an interconnect to override that selection. Ethernet is the fallback choice.
(**) vendor indicates a proprietary vendor interconnect. The specific proprietary interconnects that are supported are dictated by those that the vendor's MPI supports.

Table 32.4.2: Available MPIs for Linux/UNIX Platforms

MPI	Syntax (flag)	Communication Library	Notes
hp	-mpi=hp	HP MPI	General purpose for SMPs and clusters
intel	-mpi=intel	Intel MPI	General purpose for SMPs and clusters
mpich2	-mpi=mpich2	MPICH2	For both SMPs and Ethernet clusters (UNIX only)
sgi	-mpi=sgi	SGI MPI for Altix	Only for SGI Altix systems (SMP); must start ANSYS FLUENT on a system where parallel node processes are to run
vendor	-mpi=vendor	Vendor MPI
openmpi	-mpi=openmpi	Open MPI	Open source MPI-2 implementation. For both SMPs and clusters.

Table 32.4.3: Supported MPIs for Linux/UNIX Architectures (Per Interconnect)

Architecture	Ethernet	Myrinet*	Infiniband	Proprietary Systems
lnx86	hp (default), mpich2	hp	hp	-
lnamd64	hp (default), intel	hp (default), openmpi	hp (default), intel, and openmpi	-
lnia64	hp (default), intel	hp	hp (default), intel	sgi
aix51_64	vendor (default), openmpi	-	-	vendor
hpux11_ia64	vendor (default)	-	-	vendor
ultra_64	vendor (default)	-	-	vendor

(*) Both MX and GM Myrinet protocols are supported. ANSYS FLUENT will automatically detect which type is running on the system and will use that particular protocol. You only have to supply the -pmyrinet option. If the hardware supports it, the installation and usage of Myrinet MX is recommended (please consult your Myrinet vendor for applicability).