Editing Parallel Computing (section)

===Setting the environment variables and how to run===

The <tt>RSF_CLUSTER</tt> variable holds, for each node, the name or IP address of that node (in a format that can be used by ssh), followed by the number of threads on the node. For example, creating 26 threads and sending them on 4 nodes, using respectively 6 CPUs on the first node, 4 CPUs on the second, and 8 CPUs on each of the last two nodes:
<syntaxhighlight lang="bash">
export RSF_CLUSTER='140.168.1.236 6 140.168.1.235 4 140.168.1.234 8 140.168.1.233 8'
</syntaxhighlight>

The <tt>RSF_THREADS</tt> variable holds the sum of the numbers of threads on all nodes, i.e.:
<syntaxhighlight lang="bash">
export RSF_THREADS=26
</syntaxhighlight>
If <tt>RSF_CLUSTER</tt> is not defined, <tt>RSF_THREADS</tt> can be used to override the auto-detected number of threads used on the local host. This can be useful in the case of processes using a large amount of memory.

In Beowulf-type clusters in which communication of the processor with the local disk is much faster than with the shared network storage, it is important to set in the shell resource file the temporary file location to a local disk, and the <tt>DATAPATH</tt> variable to a network-visible location for global collection of results, i.e.:

<syntaxhighlight lang="bash">
export DATAPATH=/disk1/data/myname/
export TMPDATAPATH=/tmp/
</syntaxhighlight>

To execute using this method, one can then use the command <tt>pscons</tt> or avoid specifying the environment variables altogether by using,
<syntaxhighlight lang="bash">
scons -j 26 CLUSTER='140.168.1.236 6 140.168.1.235 4 140.168.1.234 8 140.168.1.233 8'
</syntaxhighlight>.