Parallel Programming Guide for HP-UX Systems

MPI

Running

Chapter 2 27

Runtime environment variables

Environment variables are used to alter the way HP MPI executes an application. The

variable settings determine how an application behaves and how an application allocates

internal resources at runtime.

Many applications run without setting any environment variables. However, applications that

use a large number of nonblocking messaging requests, require debugging support, or need to

control process placement may need a more customized conﬁguration.

Environment variables are always local to the system where mpirun runs. To propagate

environment variables to remote hosts, specify each variable in an appﬁle using the -e

option. See “Creating an appﬁle” on page 42 for more information.

Environment variables can also be set globally on the mpirun command line:

% $MPI_ROOT/bin/mpirun -e MPI_FLAGS=y -f appfile

In the above example, if some MPI_FLAGS setting was speciﬁed in the appﬁle, then the global

setting on the command line would override the setting in the appﬁle. To add to an

environment variable rather than replacing it, use the following command:

% $MPI_ROOT/bin/mpirun -e MPI_FLAGS=%MPI_FLAGS,y -f appfile

In the above example, if the appﬁle speciﬁed MPI_FLAGS=z, then the resulting MPI_FLAGS seen

by the application would be z, y.

The environment variables that affect the behavior of HP MPI at runtime are listed below and

described in the following sections:

• MPI_COMMD

• MPI_DLIB_FLAGS

• MPI_FLAGS

• MP_GANG

• MPI_GLOBMEMSIZE

• MPI_INSTR

• MPI_LOCALIP

• MPI_MT_FLAGS

• MPI_NOBACKTRACE

• MPI_REMSH

• MPI_SHMEMCNTL