Many software packages for parallel processing on a network of
workstations, for example MPI, make use of Unix's <STRONG> rsh </STRONG>
command.  This Web page will tell you what you need to know about this.

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The name "rsh" stands for "remote shell," meaning that it will 
execute a shell command at a remote machine.  For example, if you
are on the machine hp8.cs.ucdavis.edu and type 

<P> <PRE>

rsh hp10 ls /tmp

 </PRE> <P>

this will result in hp8 sending a message to hp10 to run the Unix ls (on
the directory /tmp) command there are hp10 (and send the output back
here, at hp8).

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In order to do this, you need to tell hp10 that it is OK to accept
commands from you at hp8 without asking for a password.  You can do
this by including a line

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hp8.cs.ucdavis.edu

 </PRE> <P>

in a file ~/.rhosts in your home directory at hp10.

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(Actually, in this particular case, the machines hp8 and hp10 happen
to share a common file system, so that .rhosts file will be common to
both hp8 and hp10.  By the way, they will have separate /tmp
directories.)

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In your ~/.rhosts file, make sure to put each machine name on a separate
line, and do use fully-qualified addresses, e.g. hp8.cs.ucdavis.edu
instead of just hp8.  In some cases, you may need to include <STRONG>
both </STRONG> hp8 and hp8.cs.ucdavis.edu.

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MPI etc. call <STRONG> rsh </STRONG> in order to initiate the running of
the given application program at several different machines, instead of
the user having to launch them "by hand" at each machine.