RHEL7: Why rsyslogd is not logging to /var/log/{messages,cron,maillog,secure,spooler}?

Issue

• rsyslogd is not logging to:

  /var/log/cron
  /var/log/maillog
  /var/log/messages
  /var/log/secure
  /var/log/spooler
  

• journalctl -u rsyslog or systemctl status rsyslog -l reports one of the following issues:

  ... rsyslogd[644]: fopen() failed: 'Too many open files', path: '/var/lib/rsyslog/imjournal.state.tmp'  [v8.24.0 try http://www.rsyslog.com/e/2013 ]
  ... rsyslogd[644]: action 'action 6' resumed (module 'builtin:omfile') [v8.24.0 try http://www.rsyslog.com/e/2359 ]
  ... rsyslogd[644]: action 'action 6' suspended, next retry is Wed Jan 31 09:23:42 2018 [v8.24.0 try http://www.rsyslog.com/e/2007 ]