crontab -l 45 18 * * * /path/dobackup.pl >> /var/log/back.log 2>&1
Демон запущен, из под рута скрипт отлично отрабатывает в /var/log/messages:
Jun 22 17:30:01 backupserver /USR/SBIN/CRON[11201]: (root) CMD (path/dobackup.pl >> /var/log/back.log)
Jun 22 17:35:15 backupserver crontab[11363]: (root) LIST (root)
Jun 22 17:43:22 backupserver /usr/sbin/cron[11633]: (CRON) STARTUP (1.4.7)
Jun 22 17:43:22 backupserver /usr/sbin/cron[11633]: (CRON) INFO (running with inotify support)
Jun 22 17:43:22 backupserver /usr/sbin/cron[11633]: (CRON) INFO (@reboot jobs will be run at computer's startup.)