Pacemaker by default logs messages of notice severity and higher to the system log, and messages of info severity and higher to the detail log, which by default is /var/log/pacemaker/pacemaker.log.
Logging options can be controlled via environment variables at Pacemaker start-up. Where these are set varies by operating system (often /etc/sysconfig/pacemaker or /etc/default/pacemaker).
Because cluster problems are often highly complex, involving multiple machines, cluster daemons, and managed services, Pacemaker logs rather verbosely to provide as much context as possible. It is an ongoing priority to make these logs more user-friendly, but by necessity there is a lot of obscure, low-level information that can make them difficult to follow.
The default log rotation configuration shipped with Pacemaker (typically installed in /etc/logrotate.d/pacemaker) rotates the log when it reaches 100MB in size, or weekly, whichever comes first.
If you configure debug or (Heaven forbid) trace-level logging, the logs can grow enormous quite quickly. Because rotated logs are by default named with the year, month, and day only, this can cause name collisions if your logs exceed 100MB in a single day. You can add dateformat -%Y%m%d-%H to the rotation configuration to avoid this.
