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 lam
boot(1) to start LAM, and by lamhalt(1) to terminate LAM
(note that wipe(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 pre
fix bhost. Individual users usually create their own boot
schema, especially if the configurations are simple.
EXAMPLE
Here is an example three node boot schema:
#
# example LAM host file
#
beowulf1.nd.edu cpu=2
beowulf2.nd.edu
beowulf2.nd.edu
somewhere.else.college.edu user=guest
Note that the "guest" ID is significant, since the user
has an alternate login ID on somewhere.else.college.edu.
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 particu
larly useful for running on SMP machines.
beowulf2 is listed twice, but has no specific CPU count
listed. In this case, LAM will keep a running tally of
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 sin
gle 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
lamboot(1), lamhalt(1), mpirun(1), MPI_Comm_spawn(1),
MPI_Comm_spawn_multiple(1), recon(1), wipe(1)
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