Every time a cron job is executed, an entry will be added to syslog, no matter whether the job succeeded or not. I have a couple of crons that run every minute, so syslog gets awfully cluttered with useless lines. Adding > /dev/null or > /dev/null 2>&1 to the job commands doesn’t help.
Fortunately cron logging can be configured, in /etc/default/cron. Log levels are explained in that file:
# Or, to log standard messages, plus jobs with exit status != 0:
# EXTRA_OPTS='-L 5'
#
# For quick reference, the currently available log levels are:
# 0 no logging (errors are logged regardless)
# 1 log start of jobs
# 2 log end of jobs
# 4 log jobs with exit status != 0
# 8 log the process identifier of child process (in all logs)
#
# EXTRA_OPTS=""
The default is to log the start of every job. I uncommented the last line and set it to EXTRA_OPTS="-L 0"
Then, restart the cron daemon:
/etc/init.d/cron restart