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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
       conditions 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
       information 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 running 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
       occurances 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 7.1.5b2                       June, 2008                          BHOST(5)