MOM's rcp

1. What is this rcp stuff?

The majority contents of this directory is the source code
for the rcp(1) command.  This source is from the bsd4.4-Lite
distribution.  It is copyrighted by UCB as noted in the source
files.  This code has been slightly modified in order to have
in compile on systems other than bsd4.4;  note their liberal
use of functions suchs as vwarnx() and snprintf() not found in
POSIX.   The copyright, reproduced below, clearly grants the right
to modify and redistribute the source.

 * Copyright (c) 1992, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
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 * modification, are permitted provided that the following conditions
 * are met:
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 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
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 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
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2. Why do we need it?

Within PBS, there are three cases in which MOM must move files
between her machine and some other:
	a. Pre-execution stage in of files.
	b. Post-execution stage out of files.
	c. Post-execution return of the job`s standard output and
	   standard error.

The PBS project did not wish to be dependent on NFS, AFS, or any
other distributed file system in order to support file delivery.
Nor did we wish to restrict the source/target of file movement to
those systems with a PBS server.  This ruled out using the "job"
protocol as a file transport.  Ftp(1) and ftam require the user's
password.  We did not wish to require that knowledge.  Thus rcp(1)
was selected as the transport method.   MOM uses the system(3)
library routine to execute the rcp command.

However, many rcp implementations come with a serious flaw.  They
may exit and return an exit status of zero (0), when the file was
not delivered.  If this happens, MOM would believe that the file
was delivered when it was not.  

One solution would have been to implement a new copy utility for MOM
very similar to rcp.  But this would have required it's installation
on every system to/from which the user may wish to move files.  Rather
than duplicate rcp, lets just fix it.  As only the rcp used by MOM
must be "fixed", the PBS team opted to provide a version of rcp that
works correctly.   The bsd4.4-Lite version was chosen because of the
freedom to copy and modify it granted by its copyright.


3. How is it used?

The supplied rcp source is compiled and the program is named
"pbs_rcp" in order to reduce the level of confusion on having
two "rcp"s installed on the system.  It is installed in the same
directory as MOM (pbs_mom).

When MOM invokes pbs_rcp, MOM has forked a child which as set its
effective and real uid to that of the user on whoses behalf MOM
is operation.  This child of MOM, as the user, will use system(3)
to fork a shell and execute pbs_rcp.  The path to the pbs_rcp 
is specified in building src/mom/requests.c and contains the directory
where MOM is (will be) installed.

Pbs_rcp, as in normal rcp, must be installed "setuid" and owned by root.