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)