~ # cat /opt/etc/crontab 
#-----------------------------------------------------------------
# Shell variable for cron
SHELL=/bin/sh
# PATH variable for cron
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/opt/sbin:/opt/bin
#M   S     T M W   Befehl
#-----------------------------------------------------------------

# every 4 hours daily bu
0 */4 * * * root rsnapshot hourly
# every day 1900 daily bu
0 19 * * * root rsnapshot daily
# every monday 2000 weekly bu
0 20 * * mon root rsnapshot weekly
# every month on 01.xx 2100 monthly bu
0 21 1 * * root rsnapshot monthly