Logrotate
From charlesreid1
log rotation in ubuntu 16.04 is daily by default, with 7 days of backups kept.
https://askubuntu.com/a/124959
To change this, edit /etc/logrotate.d/rsyslog
Man page for this utility is here: http://manpages.ubuntu.com/manpages/precise/man5/rsyslog.conf.5.html
It is not very nice.
A much better guide from digital ocean is here: https://www.digitalocean.com/community/tutorials/how-to-centralize-logs-with-rsyslog-logstash-and-elasticsearch-on-ubuntu-14-04
this incorporates logstash and elasticsearch. :)