password before allowing you to log in. The ultimate effect is to greatly slow down parallel application launching. For this reason, many Beowulf sites forego NIS for distributing account information.
6.4.4 PRSH Parallel Remote Shell
Throughout the course of managing a Beowulf cluster, you will encounter an endless number of tasks that will require you to execute a command on multiple nodes at a time. It is possible to use rsh as the basis for a parallel remote command execution facility. One of the authors has done just that by writing the prsh command. The motivation for such a command is that you often have to kill a process on some set of nodes, list files on a set of nodes, and generally execute any arbitrary command on a set of nodes. Rather than create a pkill, pls, and p version of every command, you only need a prsh, which will execute any command on any number of nodes. For convenience it is possible to wrap this command with shell scripts named pkill, pls, etc., that will execute the appropriate command on many nodes. Alternatively, you could create symbolic links to the command and modify prsh to execute a given command on multiple nodes based on the name under which prsh is invoked. It is likely that future versions of prsh will include these features.4 We list the prsh man page so that you can get a better idea of how to use it.
Prsh is a parallel asynchronous interface to rsh(1). It runs a command on a set of remote hostnames listed on the command line. All remote commands execute concurrently, and their standard output and standard error are delivered to prsh's stdout and stderr, respectively. The stdin of all remote commands is closed, c.f. the -n argument to rsh(1).
Prsh is particularly useful in a system area network, e.g., a Beowulf, where users and system administrators frequently need to execute commands remotely on large numbers of processors.
4You can download prsh source code from http://www.cacr.caltech.edu/beowulf/. prsh is a Perl5 script and requires that Perl5 be installed on your system.
