Editing Hostnames of Machines

Introducing STAR-CCM+ > Working with Simulations > Starting a Parallel Server > Using a Cluster of Machines > Editing Hostnames of Machines

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Editing Hostnames of Machines

A command line option permits you to edit the hostnames of the machines prescribed to the server. This is primarily for the use with batch systems.

Some clusters are set up so that each cluster node (machine) has two network cards. The first may be a default ethernet card and the second a higher-performance network card. In these circumstances the hostnames associated with the second card are not the same as those allocated to the first card. Typically the hostnames are usually appended by a string but it depends upon how the machine was configured. The batch systems do not see second cards, so when the batch system allocates nodes on which jobs can run they refer to the default cards.

However, when you run STAR-CCM+ you may want to take advantage of the higher-performance card. To do this you would need to translate the hostname provided by the batch system to the hostname you actually want to use.

Suppose you have a cluster of machines with names:

green-node1

green-node2

green-node3

.....

green-nodeN

The batch system may allocate four nodes:

green-nodeN1

green-nodeN2

green-nodeN3

green-nodeN4

However, the application wants to use the higher performance network cards which could be named:

green-nodeN1-eth1

green-nodeN2-eth1

green-nodeN3-eth1

green-nodeN4-eth1

The command line to achieve this is:

-hostregexpr /<pattern>/<substitution>/

where the "regular expression" pattern is replaced by the regular expression substitution. Regular expressions are a general way of pattern matching strings.

Also, /<pattern>/<substitution>/ is passed directly into the command:

echo $machinename | sed -s 's/<pattern>/<substitution>/g'

Examples of how you might use this technique are:

Appending a string to the end of every hostname:

-hostregexpr /\$/<string>/

So to append -eth1 you would enter:

-hostregexpr /\$/-eth1/

The dollar sign represents the end of line (or end of hostname) and replaces it with the string. At the same time, it is necessary to escape the dollar sign to prevent the command-line shell from interpreting it. Hence, the syntax is /\$/-eth1/ instead of /$/-eth1/.

Adding a string to the start of every hostname:

-hostregexpr /^/eth1-/

This would give entries such as eth1-green-nodeN1. (The ^ is the start of a line or hostname in a regular expression. There is no need to escape this character as it has no special meaning to the shell.)

Substituting a common string with another:

-hostregexpr /green/green-eth1/

This would result in green-eth1-nodeN1.

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