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 lamwipe(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.

NAME RESOLUTION

       Note  that lamboot resolves all names listed in bhost on the node in which lamboot was invoked on.  The lamboot(1) man page contains infor-
       mation about address resolution, examples on how to handle multiple network interface cards (NICs) in a node, etc.

EXAMPLE

       Here is an example three node boot schema:

       #
       # example LAM host file
       #
       server.cluster.example.com schedule=no
       beowulf1.cluster.example.com cpu=2
       beowulf2.cluster.example.com
       beowulf2.cluster.example.com
       somewhere.else.example.com user=guest

       Note that the "guest" ID is significant, since the user has an alternate login ID on somewhere.else.example.com.   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.

       Note  the  schedule=no  clause.	 This means that LAM will boot a daemon on that node, but by default, will not launch any MPI processes on
       that node.  This is handy for when you want to control your MPI applications from one node (e.g., a server), but don't want to run any  MPI
       applications on it.  In some environments this is the default (e.g., BProc).  See the LAM User's Guide for more details.

       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

       LAM User's Guide, lamboot(1), lamhalt(1), mpirun(1), MPI_Comm_spawn(1), MPI_Comm_spawn_multiple(1), recon(1), lamwipe(1)

LAM 7.1.4							    July, 2007								  BHOST(5)