Stop Munin messages from /var/log/syslog

Depends on syslog. If use rsyslog(Ubuntu/Debian), you can edit /etc/rsyslog.d/50-default.conf:

#
# First some standard log files.  Log by facility.
#
:msg,contains,"/etc/munin/plugins/apt_all update 7200" ~
auth,authpriv.*                 /var/log/auth.log

It's a cron syslog message(not Munin).

If you do not use apt_all munin plugin you can just comment out this cron job in

/etc/cron.d/munin-node

This isn't a munin message, it's a cron message. It's possible to stop all cron messages from going into /var/log/syslog, and/or to send them somewhere else, but that's all. Would you like to do that?

To add to the answer above (I cannot edit or comment): for newer Munin versions the information provided by syslog is different:

CRON[9413]: (root) CMD (if [ -x /etc/munin/plugins/apt_all ]; then munin-run apt_all update 7200 12 >/dev/null; elif [ -x /etc/munin/plugins/apt ]; then munin-run apt update 7200 12 >/dev/null; fi)
CRON[9414]: (munin) CMD (if [ -x /usr/bin/munin-cron ]; then /usr/bin/munin-cron; fi)

In /etc/rsyslog.d/50-default.conf, underneath # First some standard log files. Log by facility., add following two lines:

:msg, contains, "then /usr/bin/munin-cron" ~
:msg, contains, "then munin-run apt_all update 7200 12" ~

Then restart the rsyslog process:

service rsyslog restart

Using Munin 2.0.17-2ubuntu1 on Ubuntu Saucy.