Note
 For some reason, changes made on raven with crontab -e are not taking effect. The vixie-cron daemon must be restarted: 
$ sudo /etc/init.d/vixie-cron restart
Note
 In crontabs, "%" means new line. To get a real %, use: $'\x25'
My Sample Cron
MAILTO='xed@mail.molsoft.com'

# Here is a sample cron tab that explains what goes where.
# Basically, don't put a * in the first two fields unless you
# want a LOT of action.
#
# minute
#  |   hour(0-23)
#  |    |   day of month(1-31)
#  |    |    |   month of year(1-12)
#  |    |    |    |   day of week(0-6, 0=Sunday)
#  |    |    |    |    |    COMMANDS
#  0    2    *    *    0,4   /sbin/something


# Normal style of entries.
30 * * * * /home/xed/somegood_hourly_script >/dev/null 2>&1
55 8 * * * /home/xed/somegood_daily_script

# Birthday reminder example.
0 0 17 1 * echo "Happy Birthday"

# Example alarm.
30,42 14 * * 1,2,4,5   /usr/bin/play -q /home/xed/collection/sounds/cattle.wav

# Check if drive is full. If not, igonore. If it is, send email.
22 3 * * 0    df | grep "100. /"