The Linux-HA (High-Availability Linux) project provides a high-availability (clustering) solution for Linux, FreeBSD, OpenBSD, Solaris and Mac OS X which promotes reliability, availability, and serviceability (RAS). The project's main software product is Heartbeat, a GPL-licensed portable cluster management program for high-availability clustering. Heartbeat is a daemon that provides cluster infrastructure (communication and membership) services to its clients. This allows clients to know about the presence of peer processes on other machines and to easily exchange messages with them. In order to be useful to users, the Heartbeat daemon needs to be combined with a cluster resource manager (CRM) which has the task of starting and stopping the services (IP addresses, web servers, etc.) that the cluster will make highly available. Pacemaker is the preferred CRM for clusters based on Heartbeat.