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 7.1.4                                          July, 2007                                           BHOST(5)