how to stop systemd spamming syslog with messages

systemd has a bad habit of spanning the system log with messages every time a user logs in. This is especially annoying on busy systems and/or if using nagios for monitoring it.

To get rid of the logspam:

sudo loginctl enable-linger NAGIOSUSER

After the above, there are still messages about starting and Removing sessions :(

#Add Filter
sudo -s
echo 'if ($programname == "systemd-logind" or $programname == "systemd") and ($msg contains "Starting Session" or $msg contains "Started Session" or $msg contains "Removed session" or $msg contains "New session" or $msg contains "Created slice" or $msg contains "Starting user-") then stop' >/etc/rsyslog.d/ignore-systemd-session-slice.conf
#Restart Syslog
systemctl restart rsyslog
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