In some systems (Debian) logging for cron is not enabled by default. In /etc/rsyslog.conf (sudo nano /etc/rsyslog.conf
) the line:
# cron.* /var/log/cron.log
should be edited uncommented to:
cron.* /var/log/cron.log
After that, you need to restart rsyslog via
/etc/init.d/rsyslog restart