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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 multi‐
       computer running LAM.  It is used by recon(1) to verify initial	condi‐
       tions 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 num‐
       ber 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 sim‐
       ple.

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	alter‐
       nate  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 applica‐
       tions 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 oper‐
       ates 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)
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