User session messages in the system log on Centos 7

Here's how to get rid of those annoying systemd messages that flood /var/log/messages on Centos 7.

Filter them out with an rsyslog filter script in /etc/rsyslog.d -

echo 'if $programname == "systemd" and ($msg contains "Starting Session" or $msg contains "Started Session" or $msg contains "Created slice" or $msg contains "Starting user-" or $msg contains "Starting User Slice of" or $msg contains "Removed session" or $msg contains "Removed slice User Slice of" or $msg contains "Stopping User Slice of") then stop' >/etc/rsyslog.d/ignore-systemd-session-slice.conf

Then restart rsyslog

systemctl restart rsyslog

Shamelessly stolen from Red Hat here