I was wondering if any of you have experience debugging cron jobs.

Here's my problem:  I have three cron jobs that I run from root's
crontab that look like this (with variations for different uids):

0 1 * * *       su rpg -c /home/rpg/bin/backup-machine1

When I run these scripts from the command line, they work fine.  The
scripts just invoke rsync (running "locally," between two different
nfs directories mounted on the same machine) to do some backups.

But, when I invoke them from cron, I get responses like this:

From: root at tsathoggua.mydomain (Cron Daemon)
To: root at tsathoggua.mydomain
Subject: Cron <root at tsathoggua> su rpg -c /home/rpg/bin/backup-machine1
Date: Mon, 24 Jun 2002 01:00:01 -0500 (CDT)

building file list ... rsync: error writing 4092 unbuffered bytes - exiting: Broken pipe
rsync error: error in rsync protocol data stream (code 12) at io.c(464)

Any idea why this should happen?

Thanks,
R