BHOST(5)							 LAM FILE FORMATS							  BHOST(5)

NAME

       bhost - LAM boot schema (host file) format

SYNTAX

       #
       # comments
       #
       <machine> [cpu=<cpucount>] [user=<userid>]
       <machine> [cpu=<cpucount>] [user=<userid>]
	...

DESCRIPTION

       A  boot schema describes the machines that will combine to form a multicomputer running LAM.  It is used by recon(1) to verify initial con-
       ditions for running LAM, by lamboot(1) to start LAM, and by lamhalt(1) to terminate LAM (note that  wipe(1)  has  been  deprecated  by  the
       lamhalt(1) command).

       The  particular	syntax of a LAM boot schema is sometimes called the "host file" syntax.  It is line oriented.  One line indicates the name
       of a machine, typically the full Internet domain name, an optional number of CPUs available on that machine, and optionally the userid with
       which to access it.

       Common  boot  schema  for a particular site may be created by the system administrator and placed in the installation directory under etc/.
       They typically start with the prefix bhost.  Individual users usually create their own boot schema, especially if  the  configurations  are
       simple.

EXAMPLE

       Here is an example three node boot schema:

       #
       # example LAM host file
       #
       beowulf1.nd.edu cpu=2
       beowulf2.nd.edu
       beowulf2.nd.edu
       somewhere.else.college.edu user=guest

       Note  that  the	"guest" ID is significant, since the user has an alternate login ID on somewhere.else.college.edu.  Additionally note that
       beowulf1 has a CPU count of 2 listed (a CPU count of 1 is assumed if it is not given).  This value is used by mpirun(1), MPI_Comm_spawn(2),
       and  MPI_Comm_spawn_multiple(2) for the "C" (or CPU) notation that specifies how many ranks to start.  This is particularly useful for run-
       ning on SMP machines.

       beowulf2 is listed twice, but has no specific CPU count listed.	In this case, LAM will keep a running tally of the total  number  of  CPUs
       for  that  host.  Hence, LAM will calculate that beowulf2 has two CPUs available for use.  Calculating the number of CPUs by counting occu-
       rances of a hostname is useful in a batch environment where a hostfile may list the same hostname multiple times, indicating that the batch
       scheduler has allocated multiple CPUs for a single job (e.g., PBS operates this way).

       For the above-mentioned schema, the command "mpirun C foo" would start five instances of the foo program; two on beowulf1, two on beowulf2,
       and one on somewhere.else.

FILES

       $LAMHOME/etc/bhost.def		 default boot schema file

SEE ALSO

       lamboot(1), lamhalt(1), mpirun(1), MPI_Comm_spawn(1), MPI_Comm_spawn_multiple(1), recon(1), wipe(1)

LAM 6.5.8							  November, 2002							  BHOST(5)